JP2001126697A - Nonaqueous electrolyte battery and separator therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte battery with a separator that has a less thickness, good balance between the diameter of pores and the mechanical strength, and noticeable winding ability. SOLUTION: The separator for a non-aqueous electrolyte battery consists of a non-woven fabric coated with polyolefin resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for a non-aqueous electrolyte battery having a small thickness, a small pore size, a high mechanical strength and an excellent winding property, and a non-aqueous solution having excellent load characteristics using the separator. The present invention relates to an electrolyte battery.

[0002]

2. Description of the Related Art A porous film is generally used as a separator used in a non-aqueous electrolyte battery such as a lithium secondary battery, but the porous film has an extremely small pore diameter of about 0.1 μm or less. Each time the electrode expands during charging and discharging, the non-aqueous electrolyte is extruded from the porous film to the electrode side, increasing the electrical resistance between the porous film and the electrode interface, leading to a rapid decrease in capacity. there were.

Recently, many patent applications have been filed for separators made of non-woven fabric as separators replacing porous films. For example, JP-A-7-37571 discloses a paper-like sheet obtained by mixing 10 to 40% by weight of m-aramid fibrids and 90 to 60% by weight of heat-resistant short fibers. Is 0.01-0.
A battery separator having a thickness of 1 μm is disclosed. JP-A-9-64560 discloses a separator characterized by adding isolated cellulose microfibrils to a cellulose fiber or a composite of a cellulose fiber and a synthetic polymer. JP-A-7-302584 discloses that the average fiber length is 0.2 to 1.5 mm and the average fiber diameter is 0.05 to 1 μm.
m, comprising a nonwoven fabric comprising at least 50% by weight of microfibrillated fibers of an organic synthetic polymer.

[0004] In the case of separators made of these nonwoven fabrics, when the thickness is reduced, there is a tendency that problems occur in the pore diameter and mechanical strength. Especially when the thickness is 30 μm or less,
Large through-holes called pinholes tend to occur, and even if pinholes are not formed, the pores are often large, in which case not only the electrolyte retention is reduced,
Immediately after assembling the battery, the open circuit voltage dropped, which sometimes hindered charging. Conversely, in the case of a uniform nonwoven fabric having a small pore size and a narrow pore size distribution, the mechanical strength of the nonwoven fabric, such as tensile strength, tear strength, and puncture strength, is extremely weak, which may hinder secondary processing and battery assembly. There was something. In addition, when heat treatment of the nonwoven fabric is attempted to increase the mechanical strength, in some cases, the film may be formed into a film and the pores may be crushed, and it is difficult to balance the size of the pores and the mechanical strength. .

Japanese Patent Application Laid-Open No. Sho 60-136161 discloses that an electrically insulating adhesive resin which melts and flows at a temperature of 120 ° C. or less is adhered to at least one surface of a microporous sheet. A lithium battery separator material having an electric resistance of ^-2 Ωdm ² / sheet or less is disclosed. This is because when the internal temperature rises rapidly due to a short circuit etc. in the battery, the adhesive resin adhering to the separator material melts, immediately closing the hole of the separator material and stopping the current, The purpose is to prevent the temperature rise and the internal pressure from rising any further.The fiber surface of the wet nonwoven fabric is positively coated with polyolefin resin to control the pore size of the separator and to increase the mechanical strength. Is different from Also, as described in the same publication, the adhesive resin is impregnated, applied, and adhered to the microporous sheet by a method of spraying and dried, and the bonding strength between the adhesive resin and the microporous sheet or the adhesive resin is insufficient. Therefore, a separator having high mechanical strength cannot be obtained. In order to obtain high mechanical strength, the amount of adhesion resin must be considerably increased, in which case the pores of the separator are crushed or the thickness becomes unnecessarily thick, and the electrical resistance value of the separator increases. And other problems. Further, the method of bonding the adhesive resin causes problems such as crushing of the pores of the separator and unnecessarily thickening of the separator, resulting in uneven thickness and increased electric resistance of the separator.

[0006] Japanese Patent Application Laid-Open No. 10-6453 discloses that as a battery separator, at least two kinds of resins, a resin layer having voids made of para-oriented aromatic polyamide and a resin constituting voids made of thermoplastic polymer. A para-aramid-based porous film made of a material is disclosed. This is characterized in that when the temperature rises, the resin made of the thermoplastic polymer melts, closes the voids in the resin layer made of para-oriented aromatic polyamide, and the resin layer made of para-oriented aromatic polyamide keeps the film shape. And
In this case, the thermoplastic polymer particles or the resin layer made of the thermoplastic polymer is entangled with the fibrils of the para-oriented aromatic polyamide, trapped, forms voids in a fixed state, controls the pore diameter of the separator, and This is different from a wet nonwoven fabric in which the fiber surface is positively coated with a polyolefin resin for the purpose of increasing the mechanical strength.

Japanese Patent Application Laid-Open No. H11-195410 discloses that at least one surface of a separator made of a microporous film of a polyolefin resin, which is in contact with a positive electrode or a negative electrode, is provided with particles or fibers of a polyolefin resin and has a surface roughness of at least one. 1 μm
A lithium secondary battery having a size of not less than 20 μm or less is disclosed. The purpose of this separator is to prevent the electrolyte solution between the electrode groups from being depleted and to prevent the charge / discharge cycle life from being shortened. In this case, the particles or fibers of the polyolefin resin do not have the effect of increasing the mechanical strength of the separator.Therefore, the fiber surface of the wet nonwoven fabric is positively controlled with the polyolefin resin for the purpose of controlling the pore size of the separator and increasing the mechanical strength. It is different from the one made by coating.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems found in the prior art. That is, an object of the present invention is to provide a non-aqueous electrolyte battery having a small thickness, a well-balanced pore diameter and mechanical strength, and a highly reliable non-aqueous electrolyte battery separator and a load characteristic using the same. To provide.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors coated the fiber surface of the wet-laid nonwoven fabric with a polyolefin resin, thereby reducing the thickness and improving the balance between the pore diameter and the mechanical strength. It has been found that a highly reliable non-aqueous electrolyte battery separator and a non-aqueous electrolyte battery having excellent load characteristics can be manufactured.

That is, the present invention relates to a separator for a non-aqueous electrolyte battery comprising a wet non-woven fabric, wherein the fiber surface of the non-woven fabric is coated with a polyolefin resin. is there.

The present invention is a separator for a non-aqueous electrolyte battery comprising a wet nonwoven fabric, wherein the polyolefin resin coating the fiber surface of the wet nonwoven fabric is an acrylic copolymer.

The present invention relates to a separator for a non-aqueous electrolyte battery comprising a wet nonwoven fabric, wherein the ratio of oxygen atoms to carbon atoms present on the surface of the separator is 0.15 or less. This is a separator for a liquid battery.

The present invention relates to a separator for a non-aqueous electrolyte battery comprising a wet nonwoven fabric, which has a Young's modulus in the flow direction of 5%.
It is characterized by being at least 00 MPa.

The present invention is a non-aqueous electrolyte battery provided with the non-aqueous electrolyte battery separator of the present invention.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The wet nonwoven fabric in the present invention refers to a nonwoven fabric produced by a wet papermaking method. In the wet papermaking method, usually, a slurry is prepared by uniformly dispersing fibers in water using a dispersing aid, a thickener and the like so that the solid content concentration is about 0.1 to 5% by weight, and Water is added to the mixture to dilute it so that the solid concentration becomes 0.1 to 0.001% by weight to obtain a dilute aqueous slurry, which is formed into a sheet using a paper machine. As a paper machine, fourdrinier paper machine,
Examples thereof include a round paper machine, an inclined paper machine, and a combination machine including a combination thereof.

The fibers constituting the wet nonwoven fabric according to the present invention include bacterial cellulose produced by microorganisms, wood pulp, straw, bagasse, kozo, mizu, manila hemp, esparto, cotton linter, gumpy, jute, bamboo,
Non-wood fibers and non-wood pulp such as reeds, papyrus, kenaf, ramie, fibrillated fibers of these, rayon, cellulose, cupra, polynosic, acetate, acrylic, polyolefin, polyester, polyamide, polyimide, polyarylate, polyetherketone ( PE
K), polyetheretherketone (PEEK), polyetherimide (PEI), polyamideimide (PA
I) monofilaments, composite fibers, fibrillated fibers, various types of resins such as polyphenylene sulfide (PPS), polyether sulfone (PES), polysulfone, polyphenylene bisbenzothiazole, polyvinyl alcohol, and ethylene-vinyl alcohol copolymer Heat fusion fiber, glass fiber, micro glass fiber, alumina fiber,
Inorganic fibers such as alumina / silica fiber, ceramic fiber, zirconia fiber, rock wool, tyrano fiber, silicon carbide fiber, potassium titanate fiber, alumina whisker, aluminum borate whisker, colloidal alumina, colloidal silica, epoxy resin, fluorine resin, Examples include vinyl acetate, polyvinyl acetate, alginic acid, starch, various latexes and emulsions.

As the organic fiber used in the present invention, a splittable conjugate fiber is preferably used because a wet nonwoven fabric can be easily made thin. In addition, monofilaments, composite fibers, and splittable composite fibers having polyvinyl alcohol or an ethylene-vinyl alcohol copolymer in at least one component are preferably used because mechanical strength sufficient to stably wind up is obtained.

The fineness of the organic fibers constituting the wet nonwoven fabric used in the present invention is preferably 3 denier or less, more preferably 1 denier or less. When the thickness is larger than 3 denier, the nonwoven fabric tends to be thick, and uneven thickness tends to occur. The fiber length is preferably 1 to 30 mm, more preferably 3 to 15 mm. If the fiber length is shorter than 1 mm, the entanglement between the fibers is small, and the sheet strength is weakened. On the other hand, 30m
If the length is longer than m, the fibers tend to be twisted to cause uneven thickness and the formation tends to be uneven.

In the present invention, the basis weight of the wet nonwoven fabric prior to coating the polyolefin resin is preferably ^{5~25g / m 2, 10~20g / m} 2 is more preferable. 5g /
becomes lighter than m ^2, the mechanical strength of the wet-laid nonwoven fabric is weak,
Easy to handle. On the other hand, if it exceeds 25 g / m ² , it is difficult to reduce the thickness.

Examples of the polyolefin resin in the present invention include polyethylene, polypropylene, and polymethylpentene. Of these, polyethylene having a low melting point is preferable. Examples of the use form of the polyolefin resin include emulsions, solutions, powders, and fibrous forms. Among these, ease of processing into a wet nonwoven fabric,
Emulsions are preferred because they can be uniformly coated without blocking the pores of the wet nonwoven fabric. In addition, an acrylic copolymer polyolefin resin is particularly preferable because of its excellent bonding strength to the fiber surface.

When an emulsion of a polyolefin resin is used, a surfactant-free and emulsifier-free emulsion is particularly preferred. When a surfactant or an emulsifier is mixed, a side reaction is caused inside the battery to cause a reduction in capacity, and a problem is likely to occur in battery characteristics.

The molecular weight of the polyolefin resin in the present invention is preferably 10,000 or more, and when a component less than 10,000 is contained, the content of the component is preferably 1% or less.

In order to reduce O / C, the coating amount of the polyolefin resin in the present invention is preferably 0.1% by weight or more based on the weight of the wet nonwoven fabric. In order to increase the strength of the wet nonwoven, the density of the wet nonwoven is 0.5
g / cm ³ or less, 10% by weight or more, 0.5 g / cm ³
When it is not less than cm ^3, the coating amount is preferably not less than 1% by weight. The upper limit of the coating amount is preferably 50% by weight.
If the content is more than 50% by weight, the polyolefin resin tends to be formed into a film by the subsequent heat and pressure treatment and the pores tend to be crushed.

The polyolefin resin covers not only the fibers on the surface of the wet nonwoven fabric but also the fibers inside the nonwoven fabric.
Here, the coating amount means the coating amount for the entire wet nonwoven fabric, and does not mean the coating amount for only the wet nonwoven fabric surface. Therefore, the coating amount of the polyolefin resin can be determined from the weight difference between the wet nonwoven fabric before and after coating the polyolefin resin.

The thickness of the separator for a non-aqueous electrolyte battery in the present invention is preferably 5 to 30 μm, more preferably 10 to 25 μm.
m is more preferred. When the thickness is less than 5 μm, the mechanical strength tends to be insufficient. On the other hand, when the thickness is more than 30 μm, the electrode area that can be accommodated in the battery can becomes small, and the capacity of the nonaqueous electrolyte battery tends to decrease.

As a method for producing a wet nonwoven fabric in which the polyolefin resin of the present invention covers the fiber surface, for example, a polyolefin emulsion is applied to the wet nonwoven fabric by impregnation, coating, spraying, or the like.
The excess liquid on the surface and inside of the nonwoven fabric is squeezed out by passing between the rubber rolls of the book, and dried using a constant temperature drier, an air drier, a Yankee drier, a cylinder drier or the like. Then, in a state where at least two facing sides of the wet nonwoven fabric are fixed or under tension,
Temperature around the melting point of polyolefin resin-30 ° C from the melting point
The fiber surface is coated with a polyolefin resin by performing a heat treatment at a low temperature for at least 30 minutes or a hot press at a similar temperature using a hot press or a calender. As a result, the polyolefin resin is preferentially coated on the surface and inside of the wet nonwoven fabric mainly from the portion where the fibers overlap, and as the amount of coating increases, the entire wet nonwoven fabric is coated. The coating shape at this time, when the coating amount is small, coating is performed in a state where the fiber shape is left along the fiber surface, and when the coating amount is large to some extent, coating is performed in a film shape while leaving voids between fibers. . The coating with the polyolefin resin increases the interlaminar strength of the wet nonwoven fabric, and as a result, the mechanical strength is significantly increased.

For example, when an emulsion is used, the amount of the polyolefin resin adhering to the wet nonwoven fabric can be optimized by adjusting the concentration of the polyolefin emulsion, and the surplus liquid on the surface and inside of the nonwoven fabric can be squeezed out. Subsequent drying and heat treatment can prevent the excess polyolefin resin from forming a film and completely closing the voids of the wet nonwoven fabric.
By coating the fiber surface with the polyolefin resin in this manner, the pore size of the wet nonwoven fabric can be reduced, and therefore, the electrolyte retention as a non-aqueous electrolyte battery separator is also improved.

The maximum pore diameter of the separator for a non-aqueous electrolyte battery in the present invention is preferably 20 μm or less. The maximum pore diameter is determined by measuring according to the bubble point method specified in ASTM F-316-80. If the maximum pore diameter is larger than 20 μm, the open circuit voltage may be significantly reduced, which may hinder charging.

The separator for a non-aqueous electrolyte battery of the present invention has a ratio of oxygen atoms to carbon atoms present on the surface (O / C).
Is preferably 0.15 or less. O / C varies greatly depending on the material of the fiber constituting the wet nonwoven fabric,
The O / C is reduced by coating the fiber surface of the wet nonwoven fabric with the polyolefin resin. For example, when a polar group such as a hydroxyl group is present, the O / C increases, the hydroxyl group reacts with lithium ions, and the amount of lithium ions involved in the battery reaction decreases. Will drop. However, when the fiber surface is coated with a polyolefin resin, a polar group such as a hydroxyl group that adversely affects the battery reaction is blocked, so that the capacity is unlikely to be reduced by repeated charge and discharge.
As a result of intensive studies by the present inventors, it has been found that when O / C is 0.15 or less, the degree of capacity reduction is small.

Regarding the mechanical strength of the separator for a non-aqueous electrolyte battery according to the present invention, the Young's modulus in the flow direction is used as an index. The tensile strength is not suitable because it greatly varies depending on the basis weight of the wet nonwoven fabric constituting the separator for a nonaqueous electrolyte battery. Since the Young's modulus depends on the thickness of the wet nonwoven fabric forming the separator for a non-aqueous electrolyte battery, it is suitable as an index of the mechanical strength of the thin separator for a non-aqueous electrolyte battery in the present invention. For example, when comparing two non-aqueous electrolyte battery separators having the same degree of tensile strength and different thicknesses, the thinner the thickness, the higher the Young's modulus. And, the higher the Young's modulus, the less likely to break during winding, and the better the workability during battery assembly.

The Young's modulus in the flow direction of the separator for a non-aqueous electrolyte battery according to the present invention is not less than 500 MPa. Here, the flow direction refers to the longitudinal direction of the wet nonwoven fabric forming the separator for a non-aqueous electrolyte battery, and is the same as the machine directory in the manufacturing process of the wet nonwoven fabric. If the Young's modulus in the flow direction is less than 500 MPa, it cannot withstand the tension of the winding machine, easily breaks, and tends to hinder battery assembly.

Since the separator for a non-aqueous electrolyte battery of the present invention is made of a wet nonwoven fabric, the pore diameter is at least 10 times larger than that of a porous film. Therefore, it has characteristics of excellent load characteristics, that is, excellent in electrolyte absorbing property and electrolyte retaining property, and the degree of capacity reduction is small even when charge and discharge are repeated at a high current density.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. The content of the present invention is not limited to this embodiment. still,
% Means% by weight.

<Preparation of Negative Electrode Active Material> Petroleum pitch was fired to obtain coarse-grained pitch coke. This coarse-grained pitch coke was pulverized to a powder having an average particle diameter of 6 μm, and the powder was fired at 1000 ° C. in an inert gas to remove impurities to produce a coke powder, which was used as a negative electrode active material.

<Preparation of Negative Electrode> Negative electrode active material coke powder 9
After 0% and 10% of polyvinylidene fluoride binder were kneaded to prepare a negative electrode mixture, N-methylpyrrolidone was added to form a slurry to prepare a negative electrode mixture slurry. This negative electrode mixture slurry is uniformly applied to both sides of a 100 μm-thick strip-shaped copper foil as a negative electrode current collector, dried, and compression-molded using a roller press to obtain a negative electrode having a thickness of 180 μm, a width of 55 mm, and a length of 556 mm. Was prepared.

[0037] <Preparation of positive electrode> the positive electrode active material LiCoO ₂ 9
A positive electrode mixture was prepared by kneading 0%, conductive graphite powder 6%, and binder polyvinylidene fluoride 4%, and then N-methylpyrrolidone was added to form a slurry to prepare a positive electrode mixture slurry. This positive electrode mixture slurry is uniformly applied to both sides of a 20 μm-thick strip-shaped aluminum foil serving as a positive electrode current collector, dried, and compression-molded using a roller press, and has a thickness of 150 μm, a width of 53 mm, and a length of 528 mm. A positive electrode was produced.

<Preparation of Separator for Nonaqueous Electrolyte Battery>

Example 1 Polypropylene fiber (fineness: 0.7 denier, fiber length: 5 m)
m) 70% core-sheath conjugate fiber composed of polypropylene and an ethylene-vinyl alcohol copolymer (denier 2 denier,
A slurry in which 30% of a fiber having a fiber length of 10 mm was dispersed in water was prepared using a pulper, and was wet-laid using an inclined paper machine to produce a wet nonwoven fabric having a basis weight of 10 g / m ² . The nonwoven fabric was passed between two stainless steel rolls set at 130 ° C., and subjected to a pressure treatment under a condition of a press pressure of 40 kgf / cm ² to adjust the thickness to 20 μm. 1% solid content
Impregnated with the low density polyethylene emulsion solution of
The excess liquid on the surface and inside of the nonwoven fabric was squeezed out with a rubber roll, and then dried at 90 ° C. Thereafter, the nonwoven fabric was passed between two stainless steel rolls set at 130 ° C. and subjected to a pressure treatment under a condition of a press pressure of 40 kgf / cm ² to adjust the thickness to 15 μm, thereby obtaining a separator for a nonaqueous electrolyte battery. .

Example 2 A wet nonwoven fabric having a basis weight of 10 g / m ² and a thickness of 15 μm was prepared in the same manner as in Example 1 except that the emulsion was impregnated with a low-density polyethylene emulsion solution prepared to have a solid content of 3%. It was prepared and used as a separator for a non-aqueous electrolyte battery.

Example 3 A wet nonwoven fabric having a basis weight of 10 g / m ² and a thickness of 15 μm was prepared in the same manner as in Example 1 except that the emulsion was impregnated with a low-density polyethylene emulsion solution prepared to have a solid content of 5%. It was prepared and used as a separator for a non-aqueous electrolyte battery.

Example 4 Example 1 was repeated except that the emulsion was impregnated with a low-density polyethylene emulsion solution prepared to have a solid content of 20%.
In the same manner as described above, a wet nonwoven fabric having a basis weight of 11 g / m ² and a thickness of 15 μm was prepared, and used as a separator for a non-aqueous electrolyte battery.

Example 5 A basis weight of 1 was obtained in the same manner as in Example 1 except that the low-density polyethylene emulsion solution having a solid concentration of 40% was impregnated twice.
A wet nonwoven fabric having a thickness of 5 g / m ² and a thickness of 25 μm was prepared and used as a separator for a non-aqueous electrolyte battery.

Example 6 A basis weight of 1 was obtained in the same manner as in Example 1 except that the low density polyethylene emulsion solution having a solid content of 50% was impregnated twice.
A wet nonwoven fabric having a thickness of 6 g / m ² and a thickness of 27 μm was prepared and used as a separator for a non-aqueous electrolyte battery.

Example 7 A wet nonwoven fabric having a basis weight of 10 g / m ² and a thickness of 15 μm was prepared in the same manner as in Example 1 except that an acrylic copolymer polyethylene emulsion solution was used instead of the low-density polyethylene. This was used as a battery separator.

Example 8 A wet nonwoven fabric having a basis weight of 10 g / m ² and a thickness of 15 μm was prepared in the same manner as in Example 2 except that an acrylic copolymer polyethylene emulsion solution was used instead of the low-density polyethylene. This was used as a battery separator.

Example 9 A wet nonwoven fabric having a basis weight of 10 g / m ² and a thickness of 15 μm was prepared in the same manner as in Example 3 except that an acrylic copolymer polyethylene emulsion solution was used instead of the low-density polyethylene. This was used as a battery separator.

Example 10 A wet nonwoven fabric having a basis weight of 11 g / m ² and a thickness of 15 μm was prepared in the same manner as in Example 4 except that an acrylic copolymer polyethylene emulsion solution was used instead of the low-density polyethylene. This was used as a battery separator.

Example 11 A wet nonwoven fabric having a basis weight of 15 g / m ² and a thickness of 25 μm was prepared in the same manner as in Example 5 except that an acrylic copolymer polyethylene emulsion solution was used instead of the low-density polyethylene. This was used as a battery separator.

Example 12 A wet nonwoven fabric having a basis weight of 16 g / m ² and a thickness of 27 μm was prepared in the same manner as in Example 6 except that an acrylic copolymer polyethylene emulsion solution was used instead of the low-density polyethylene. This was used as a battery separator.

Example 13 Polyester fiber (fineness 0.4 denier, fiber length 10 m)
m) A slurry in which 95% and 5% of polyvinyl alcohol fiber (fineness: 1 denier, fiber length: 3 mm) is dispersed in water is prepared using a pulper, and wet papermaking is performed using an inclined paper machine, and the basis weight is 18 g / m2. ² wet nonwoven fabrics were produced. The nonwoven fabric was passed between two stainless steel rolls set at 210 ° C., and subjected to a pressure treatment under a pressure of 40 kgf / cm ² to adjust the thickness to 23 μm. 1% solid content
Was impregnated with the acrylic copolymerized polyethylene emulsion solution, and the excess liquid on the surface and inside of the nonwoven fabric was squeezed out with two rubber rolls, and then dried at 90 ° C. Thereafter, the nonwoven fabric was passed between two stainless steel rolls set at 130 ° C., and subjected to a pressure treatment under a condition of a press pressure of 40 kgf / cm ² to adjust the thickness to 23 μm, thereby obtaining a separator for a nonaqueous electrolyte battery. .

Example 14 A wet nonwoven fabric having a basis weight of 18 g / m ² and a thickness of 23 μm was prepared in the same manner as in Example 13 except that an acrylic copolymer polyethylene emulsion solution having a solid content of 3% was impregnated.
This was used as a separator for a non-aqueous electrolyte battery.

Example 15 A wet nonwoven fabric having a basis weight of 18 g / m ² and a thickness of 23 μm was prepared in the same manner as in Example 13 except that an acrylic copolymer polyethylene emulsion solution having a solid content of 5% was impregnated.
This was used as a separator for a non-aqueous electrolyte battery.

Example 16 A wet nonwoven fabric having a basis weight of 19 g / m ² and a thickness of 25 μm was prepared in the same manner as in Example 13 except that an acrylic copolymer polyethylene emulsion solution having a solid content of 20% was impregnated. This was used as a separator for a liquid battery.

Example 17 A wet nonwoven fabric having a basis weight of 20 g / m ² and a thickness of 25 μm was prepared in the same manner as in Example 13 except that an acrylic copolymer polyethylene emulsion solution having a solid concentration of 40% was impregnated. This was used as a separator for a liquid battery.

Example 18 A mixture of 95% of a 16-split type splittable conjugate fiber (denier: 3 denier, fiber length: 6 mm) composed of polypropylene and ethylene-vinyl alcohol copolymer and 5% of the polyvinyl alcohol fiber used in Example 13 was dissolved in water. Was prepared using a pulper and wet-laid using an inclined paper machine to produce a wet nonwoven fabric having a basis weight of 15 g / m ² . When the cross section of the nonwoven fabric was observed with an electron microscope, the splittable conjugate fiber was almost completely split. The nonwoven fabric is passed between two stainless steel rolls set at 130 ° C., and is subjected to a pressure treatment under a condition of a press pressure of 40 kgf / cm ² to have a thickness of 25 μm.
m. This was impregnated with an acrylic copolymer polyethylene emulsion solution having a solid content of 1%, and the excess liquid on the surface and inside of the nonwoven fabric was squeezed out with two rubber rolls, and then dried at 90 ° C. Thereafter, the non-woven fabric is heated to 130 ° C.
And passed through a stainless steel roll set at a pressure of 40 kgf / cm ² to obtain a thickness of 25 kg.
It was adjusted to μm to obtain a separator for a non-aqueous electrolyte battery.

Example 19 A wet nonwoven fabric having a basis weight of 15 g / m ² and a thickness of 25 μm was prepared in the same manner as in Example 18 except that an acrylic copolymer polyethylene emulsion solution having a solid content of 3% was impregnated.
This was used as a separator for a non-aqueous electrolyte battery.

Example 20 A wet nonwoven fabric having a basis weight of 15 g / m ² and a thickness of 25 μm was prepared in the same manner as in Example 18 except that an acrylic copolymer polyethylene emulsion solution having a solid content of 5% was impregnated.
This was used as a separator for a non-aqueous electrolyte battery.

Example 21 A wet nonwoven fabric having a basis weight of 16 g / m ² and a thickness of 25 μm was prepared in the same manner as in Example 18 except that an acrylic copolymer polyethylene emulsion solution having a solid content of 20% was impregnated. This was used as a separator for a liquid battery.

Example 22 A wet nonwoven fabric having a basis weight of 20 g / m ² and a thickness of 28 m was prepared in the same manner as in Example 18 except that an acrylic copolymer polyethylene emulsion solution having a solid content of 60% was impregnated.
This was used as a separator for a non-aqueous electrolyte battery.

Comparative Example 1 A wet paper was made in the same manner as in Example 1 to produce a wet nonwoven fabric having a basis weight of 10 g / m ² . The nonwoven fabric was passed through two stainless steel rolls set at 130 ° C. as it was, and subjected to a heat and pressure treatment under a pressure of 40 kgf / cm ² to a thickness of 15 μm.
m, to give a separator for a non-aqueous electrolyte battery.

Comparative Example 2 A wet nonwoven fabric having a basis weight of 10 g / m ² and a thickness of 15 μm was prepared in the same manner as in Example 3 except that the emulsion was impregnated with a low-density polyethylene emulsion solution, dried, and then subjected to no heat-pressure treatment. And a separator for a non-aqueous electrolyte battery.

Comparative Example 3 A basis weight of 15 g / m ² and a thickness of 1 made of a polypropylene resin
A 20 μm melt-blown dry nonwoven fabric with a solid content of 2
After impregnating with a 0% low-density polyethylene emulsion solution and squeezing excess liquid on the surface and inside of the nonwoven fabric with two rubber rolls, the resultant was dried at 90 ° C. Thereafter, the nonwoven fabric was passed between two stainless steel rolls set at 130 ° C., and subjected to a pressure treatment under a condition of a press pressure of 30 kgf / cm ² to adjust the thickness to 25 μm, thereby obtaining a separator for a nonaqueous electrolyte battery. .

Comparative Example 4 A basis made of polypropylene having a basis weight of 15 g / m ² and a thickness of 25 μm
m was used as a separator for a non-aqueous electrolyte battery.

<Preparation of Non-Aqueous Electrolyte Battery> Examples 1-22
And the separator for non-aqueous electrolyte batteries prepared in Comparative Examples 1 to 4 was slit into a width of 56 mm and a length of 600 mm, and this was laminated between a negative electrode and a positive electrode, and was laminated in a spiral shape using a winding machine. The spirally wound electrode was manufactured by being wound. This is nickel-plated iron 18mm in diameter and 65m in height
m in a cylindrical battery can. At this time, the positive electrode lead and the negative electrode lead were welded to the positive electrode terminal and the negative electrode terminal, respectively. Lithium was added to a solvent in which propylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 in this battery can.
A non-aqueous electrolyte in which PF ₆ was dissolved at a concentration of 1 mol / l was injected. Next, the battery lid and the battery can were swaged and sealed to produce a cylindrical nonaqueous electrolyte battery.

The separators for non-aqueous electrolyte batteries prepared in Examples 1 to 22 and Comparative Examples 1 to 4 were measured by the following test methods, and the results are shown in Tables 1 and 2.

<Coating Amount> The difference in the weight of the wet nonwoven fabric before and after coating with the polyolefin resin was divided by the weight of the original wet nonwoven fabric and multiplied by 100 to obtain the coating amount (%) of the polyolefin resin.

<O / C> Elemental analysis was performed on the surface of the separator for a non-aqueous electrolyte battery by X-ray electron spectroscopy (ESCA) to determine the ratio of oxygen atoms (O) to carbon atoms (C).

<Maximum pore size> ASTM F316-80
The maximum pore size μ conforms to the bubble point method specified in
m) was measured.

<Young's Modulus> The separator for a non-aqueous electrolyte battery has a width of 50 mm and a length of 20 mm with respect to the flow direction.
100mm / min using a tensile tester
The Young's modulus (MPa) was determined from the SS curve when the test piece was pulled until the test piece broke at a speed of, and the average value of ten pieces was expressed.

<Woundability> When a spiral electrode was manufactured using a winding machine, meandering and breakage of the separator for the nonaqueous electrolyte battery, displacement between the electrode and the separator for the nonaqueous electrolyte battery,
The presence or absence of a short circuit of the electrode was examined. Non-aqueous electrolyte battery separators could be wound uniformly without any meandering or breakage of the separator, deviation from the electrode, or short-circuiting of the electrode. ◎ In rare cases, meandering or deviation occurred, but the winding could be performed without any problem. The sample was rated as 、, a problem occurred slightly, but was practicable, and the sample was practically difficult.

The non-aqueous electrolyte batteries prepared in Examples 1 to 22 and Comparative Examples 1 to 4 were measured by the following test methods, and the results are shown in Tables 3 and 4.

<Defective Open Circuit Voltage> The open circuit voltage was measured for 30 minutes immediately after assembling the nonaqueous electrolyte battery. The open circuit voltage was measured for each of the 100 batteries, and the number of nonaqueous electrolyte batteries whose open circuit voltage was reduced to such an extent that charging was hindered was measured.

<0.5 C Discharge Capacity> Charged to 4.2 V with a constant current of 0.5 CmA, and switched to constant voltage charging after reaching 4.2 V, so that charging was completed in a total time of 2.5 hours. . The discharge was performed at a constant current of 0.5 CmA, and the initial discharge capacity when discharging until reaching 2.7 V was 0.5 C
The discharge capacity was used.

<1C discharge capacity> At a constant current of 1 CmA.
The battery was charged to 2 V, and after reaching 4.2 V, switching to constant voltage charging was performed, so that charging was completed in 2.5 hours in total. Discharge was performed at a constant current of 1 CmA, and the first discharge capacity when discharging until reaching 2.7 V was defined as 1 C discharge capacity.

[0076]

[Table 1]

[0077]

[Table 2]

[0078]

[Table 3]

[0079]

[Table 4]

Evaluation: As is clear from the results in Table 1, the separators for non-aqueous electrolyte batteries prepared in Examples 3 to 6, 9 to 12, 15 to 17, and 20 to 22 are fibers constituting a wet nonwoven fabric. Since the surface was covered with a polyolefin resin, the pore diameter and the mechanical strength were well balanced and the winding property was excellent. Examples 1, 2, 7, 8, 13, 14, 1
The separator for a non-aqueous electrolyte battery prepared in 8, 19 is
Since the coating amount of the polyolefin resin was small, the mechanical strength was slightly weak, and a problem occurred in the winding property.

Examples 3 to 6, 9 to 12, 15 to 17, 2
The separator for a non-aqueous electrolyte battery prepared in 0 to 22,
Since the coating amount of the polyolefin resin was appropriate, the maximum pore diameter was small, and the non-aqueous electrolyte battery provided with these non-aqueous electrolyte battery separators did not have an open circuit voltage defect. Since the O / C of the separator surface was 0.15 or less, the nonaqueous electrolyte battery provided with the separator exhibited a high discharge capacity. Further, the separator exhibited a Young's modulus of 500 MPa or more, and was excellent in winding property during battery assembly.

Embodiments 1, 2, 7, 8, 13, 14, 18
Since the non-aqueous electrolyte battery separator prepared in step 2 has a somewhat small amount of polyolefin resin coverage, the maximum pore diameter is somewhat large, and the non-aqueous electrolyte battery comprising these non-aqueous electrolyte battery separators is open. There was a case where a circuit voltage defect occurred. In addition, since the Young's modulus was less than 500 MPa, there was a problem in the winding property during battery assembly.

In the separators for nonaqueous electrolyte batteries prepared in Examples 1 to 12, it was confirmed that the use of the acrylic copolymer polyolefin resin had higher mechanical strength at the same coverage.

On the other hand, the separator for a non-aqueous electrolyte battery prepared in Comparative Example 1 has a large maximum pore size and a high mechanical strength because the fiber surface of the wet nonwoven fabric constituting the separator is not coated with the polyolefin resin. It was weak. Since the mechanical strength was weak, there was a problem in the winding property, which made practical use difficult.

The non-aqueous electrolyte battery prepared in Comparative Example 1 was provided with a separator for a non-aqueous electrolyte battery having a large maximum pore diameter, and thus had a high open circuit voltage failure rate and a low capacity retention rate.

The separator for a non-aqueous electrolyte battery prepared in Comparative Example 2 had a polyolefin resin attached thereto, but had not been subjected to the heat and pressure treatment. Since the coating was insufficient, the pore diameter was large and did not contribute to the improvement of the bonding strength between the fibers, the mechanical strength was weak, and there was a problem in the winding property.

The non-aqueous electrolyte battery prepared in Comparative Example 2 was provided with a separator for a non-aqueous electrolyte battery having a large maximum pore diameter, so that the open circuit voltage defect rate was slightly higher.

The separator for a non-aqueous electrolyte battery prepared in Comparative Example 3 was produced in a step of impregnating with a polyolefin resin, in which the wet strength of the dry nonwoven fabric was remarkably weak, and frequent breakage occurred. I couldn't. Nevertheless, the manufactured non-aqueous electrolyte battery separator was partially mottled and formed into a film, and the portion could not hold the electrolyte at all, and thus did not operate as a battery in some cases.

The separator for a non-aqueous electrolyte battery used in Comparative Example 4 has a small pore size of 0.2 μm or less, and therefore has a slightly poor electrolyte retention property. The capacity was low, and the load characteristics were somewhat poor.

[0090]

According to the present invention, it is possible to obtain a separator for a non-aqueous electrolyte battery which is thin, has a good balance between pore diameter and mechanical strength, and has excellent winding properties, and a non-aqueous electrolyte battery which has excellent load characteristics. .

Claims (5)

[Claims] 1. A separator for a non-aqueous electrolyte battery, comprising a wet non-woven fabric, wherein the fiber surface of the non-woven fabric is covered with a polyolefin resin. 2. The separator for a non-aqueous electrolyte battery according to claim 1, wherein the polyolefin resin is an acrylic copolymer. 3. The non-aqueous electrolyte battery separator according to claim 1, wherein the ratio of oxygen atoms to carbon atoms present on the surface of the non-aqueous electrolyte battery separator is 0.15 or less. 4. The separator for a non-aqueous electrolyte battery according to claim 1, wherein the Young's modulus in the flow direction is 500 MPa or more. 5. A non-aqueous electrolyte battery comprising the non-aqueous electrolyte battery separator according to claim 1. Description: