JP2008235047A - Battery separator and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an internal short circuit by increasing the liquid absorption of the electrolytic solution, holding the electrolytic solution for a long time, and suppressing the growth of dendrite in the negative electrode, and the electric resistance of the separator itself is low. Provided is a separator for an alkaline battery that can suppress the thickness after liquid absorption, increase the capacity of a positive electrode mixture and a negative electrode mixture, and can be manufactured using various fibers at low cost.
A separator for an alkaline battery in which nanofibers made of an alkali-resistant polymer having a fiber diameter of 10 to 1000 nm and a dry nonwoven fabric made of an alkali-resistant polymer are laminated and integrated.
[Selection figure] None

Description

  The present invention relates to a battery separator suitable for an alkaline primary battery such as an alkaline manganese battery, a mercury battery, a silver oxide battery, and an air zinc battery, and an alkaline primary battery comprising the battery separator. Relates to a separator for an alkaline primary battery, in which a specific nano-level ultrafine fiber is laminated on a dry nonwoven fabric containing alkali-resistant fibers.

In general, a separator is used in an alkaline primary battery to separate a positive electrode active material and a negative electrode active material. This separator includes
(1) preventing an internal short circuit between the positive electrode active material and the negative electrode active material;
(2) having a high electrolyte solution absorbency in order to cause a sufficient electromotive reaction, having good ionic conductivity and low electrical resistance,
(3) The occupancy when incorporated inside the battery is small, and the amount of positive electrode active material / negative electrode active material can be increased (the battery usable time can be extended),
Various performances are required.
In order to achieve the above performance, there is a battery separator that uses polyvinyl alcohol fibers that are excellent in chemical resistance, hydrophilicity, mechanical performance, etc., and further uses cellulosic fibers etc. in order to enhance electrolyte solution absorbability, etc. It has been proposed (see, for example, Patent Document 1). However, when the battery separator of Patent Document 1 is used, in order to suppress the generation of hydrogen in the electrolyte, acicular zinc oxide is precipitated by the action of aluminum added to the zinc constituting the negative electrode. There is a problem that a short circuit due to so-called dendrite occurs, causing an abnormal drop in voltage, resulting in a short battery life.

In order to prevent an internal short circuit between the positive electrode active material and the negative electrode active material, polyvinyl alcohol fibers and cellulose fibers are beaten as alkali-resistant fibers, and a dense layer having a high fiber density and a liquid retaining layer having a low density (coarse) A battery separator having a two-layer structure combining layers) has been proposed (see, for example, Patent Document 2).
However, in the battery separator of Patent Document 2, it is difficult to achieve both good liquid absorption performance and internal short circuit prevention function, and if the ratio of the dense layer is increased to prevent short circuit due to dendrite, the liquid absorption amount decreases. There is a problem that an internal short circuit occurs due to running out of liquid and the battery life is shortened.

  On the other hand, in order to prevent an internal short circuit, the paper or nonwoven fabric which used together the alkali-resistant fiber and the cellulose fiber, and the cellophane film were used together. However, the separator is inferior in liquid absorption performance, and it is necessary to increase the paper base material in order to secure the liquid absorption amount. Therefore, the occupancy ratio of the separator inside the battery is increased, the amount of the positive electrode / negative electrode active material is limited, and the distance between the electrodes is increased due to the use of cellophane film and the increase in the paper base material. As a result, there is a problem that large capacity discharge performance cannot be obtained.

Further, in order to improve the liquid absorption performance of a paper base material using an alkali-resistant fiber, a battery separator impregnated with 0.5 to 10.0 g / m ² of a cross-linked highly water-absorbing polymer has been proposed. (For example, refer to Patent Documents 3 to 5.) However, since the separators of Patent Documents 3 to 5 cannot suppress dendrite growth, it is difficult to highly prevent a short circuit due to dendrite, which causes an internal short circuit.

  Battery separators using nano-level fibers have also been proposed (see, for example, Patent Documents 6 to 7). However, although the nano-level fibers as shown in Patent Documents 6 and 7 are effective in preventing internal short circuit caused by dendrites, the fibers themselves depend only on the retention of the electrolyte solution due to the fine capillary phenomenon of the fibers. Also, the substrate to be laminated is not specialized for holding the electrolytic solution. For this reason, there is a problem in that liquid drainage easily occurs at the end of discharge, resulting in a shortened use period.

Many of the conventional battery separators are wet nonwoven fabrics. However, the nonwoven fabrics use a large amount of water due to the manufacturing method thereof, so that the cost is high, and the large consumption of water as a resource itself is an environmental problem. .
In addition, when producing a wet nonwoven fabric, the dispersibility of the constituted fibers in water is important, and the fiber itself can pass through a wet nonwoven fabric forming step such as fineness, aspect ratio, wettability to water, water resistance, etc. There was a drawback that only non-woven fabrics could be made. In addition, wet nonwoven fabrics are dense and have few voids, so the amount of alkaline electrolyte absorbed by the separator as a whole (hereinafter referred to as total liquid absorption) is small, so high-load continuous discharge with a low negative electrode utilization rate. There is a problem that high performance cannot be expected in a field that requires high power battery performance.
On the other hand, dry nonwoven fabrics do not use water, can be manufactured at low cost, without waste of resources and without restrictions on fibers such as dispersibility, and can produce separator sheets, and are bulky and have a total liquid absorption compared to wet nonwoven fabrics. Although many can be secured, there is a problem in that the electrolyte present in the interfiber gap is structurally retained, so that the electrolyte is easily drained and the use time is shortened. In addition, the structure itself has a large unevenness to be applied as a battery separator, and a satisfactory level cannot be obtained in the maximum desired separation performance.

JP-A-6-163024 Japanese Patent Laid-Open No. 10-092411 JP-A-57-105957 JP-A-57-105958 Japanese Patent Laid-Open No. 2-0708150 JP 2005-264420 A JP 2006-244804 A

  In view of the above-mentioned problems, the object of the present invention is to increase the liquid absorbency of the electrolytic solution, hold the electrolytic solution for a long time, prevent dendrite growth in the negative electrode, thereby preventing an internal short circuit, and The separator itself has a low electrical resistance, further suppresses the thickness after absorbing the electrolyte, and can increase the capacity of the positive electrode mixture and negative electrode mixture, and is manufactured at a lower cost and using various fibers. It is to provide a possible alkaline battery separator.

  As a result of intensive studies to achieve the above object, the present inventors have laminated a fibrous material obtained by thinning an alkali-resistant polymer to a nano level on a dry nonwoven fabric using an alkali-resistant fiber. It was found that a battery separator capable of maintaining a high liquid absorption performance for a long time can be obtained. Furthermore, it has been found that the deterioration of battery performance at the end of discharge can be further suppressed by constituting the substrate with fibers having alkali resistance and high liquid absorption. And it became possible to manufacture battery separators using various fibers at low cost.

  That is, in the present invention, a nanofiber made of an alkali-resistant polymer having a fiber diameter of 10 to 1000 nm and a dry nonwoven fabric made of an alkali-resistant polymer are laminated and integrated, and 35% of the laminated and integrated sheet. A separator for an alkaline battery having a total liquid absorption amount of 5.0 to 12.0 g / g when impregnated with an aqueous KOH solution. Nanofibers are preferably vinyl alcohol polymers, cellulose polymers, or cross-linked superabsorbent polymers. It is said alkaline battery separator which consists of either of these.

  The present invention is the above alkaline battery separator in which a part of the alkali-resistant polymer constituting the dry nonwoven fabric is any one of a vinyl alcohol polymer, a cellulose polymer, and a crosslinked superabsorbent polymer.

Further, according to the present invention, the laminated sheet has an air permeability of 0.1 to 10.0 cc / cm ² / sec, and a fiber absorption amount when impregnated with 35% KOH aqueous solution is 1.0 to 3.0 g. / B, and further the above-mentioned separator for an alkaline battery in which the basis weight of the laminated and integrated nanofiber is 0.1 to 10.0 g / m ² .

  The present invention also includes (A) a step of preparing a solution in which a polymer is dissolved in a solvent capable of dissolving the polymer, and (B) nanofibers on a base fabric by an electrostatic spinning method using the solution. The alkaline battery separator is characterized by comprising a stacking process or a composite process, and the battery uses the alkaline battery separator.

  According to the present invention, the electrolyte absorbability is increased, the electrolyte is retained for a long time, is not easily subject to oxidative degradation due to the positive electrode mixture, and further, the internal short circuit is prevented by suppressing the growth of dendrite, and the separator itself Battery separators that can increase the capacity of the positive and negative electrode mixture in the battery by suppressing the thickness after absorbing the electrolyte solution at low cost and using various fibers It is possible to manufacture.

Hereinafter, the present invention will be described in detail.
In the battery separator of the present invention, it is important that the fibers laminated on the dry nonwoven fabric described later have fine voids in order to prevent internal short circuits. The fiber diameter for realizing this void needs to be a nanofiber having a diameter of 10 to 1000 nm, preferably 30 to 800 nm, and more preferably 100 to 500 nm. In the case of fibers having a diameter larger than 1000 nm, the gaps between the fibers are also increased, and the effect of preventing internal short circuit is significantly reduced. The smaller the fiber diameter, the smaller the void, which is more preferable. However, when the diameter is 10 nm or less, the void is too small and the internal resistance increases, and conversely the battery performance decreases.
In addition, the fiber diameter in this invention means the diameter in the cross section of the fiber obtained from the electron micrograph of the fiber aggregate image | photographed by 5000 times, Randomly extract 50 and measure the fiber diameter with a ruler. It is the average value calculated by the numerical value.

  In the present invention, the laminated nanofibers must be composed of an alkali-resistant polymer. The alkali-resistant polymer used in the present invention is not particularly limited as long as it can be dissolved in a molten or volatile solvent. For example, polyvinyl alcohol-based polymer, cellulose-based polymer, polyvinylidene fluoride, and polyvinylidene fluoride. -Hexafluoropropylene copolymer, polymethyl methacrylate, polyvinyl chloride, polyvinyl chloride-acrylate copolymer, polyimide, polyethylene, polypropylene, polyethyleneimide, polybenzimidazole, polyarylate, polyethylene sulfide, nylon 12, nylon 4 , 6 and the like, polyethylene oxide, polypropylene oxide, polyvinyl pyrrolidone, polyvinyl acetate, collagen, etc., and these may be used alone or as a mixture of two or more. It can be used. Furthermore, it is also possible to use a mixture of one or more organic or inorganic powders in the polymer.

  Further, the separator for an alkaline battery of the present invention needs to have a total liquid absorption of 5.0 to 12.0 g / g when impregnated with 35% KOH aqueous solution. Compared to wet nonwoven fabrics, dry nonwoven fabrics have a bulky structure and large inter-fiber voids, so that a large amount of electrolyte can be retained, and the reactivity during high-load continuous discharge with a low negative electrode utilization rate is good, resulting in high power. However, in order to obtain such characteristics, the total liquid absorption needs to be 5.0 to 12.0 g / g, preferably 7. 0 to 11.0 g / g. When the total liquid absorption is less than 5.0 g / g, not only the reactivity at high-load continuous discharge is lowered, but also the battery life is liable to decrease due to liquid drainage. On the other hand, if the total liquid absorption amount is larger than 12.0 g / g, the thickness after liquid absorption is increased and the amount of the electrode material is limited, resulting in a decrease in battery performance.

In the present invention, the polymer constituting the nanofiber is preferably a polyvinyl alcohol (hereinafter referred to as PVA) polymer. PVA has good alkali resistance and is hydrophilic, and is therefore well-suited with an alkaline electrolyte and is suitable. The PVA polymer is not particularly limited, but the viscosity average degree of polymerization is preferably 1000 or more, particularly 1500 or more from the viewpoint of practical mechanical performance, and is preferably 5000 or less from the viewpoint of spinnability and cost. . For the same reason, the saponification degree is preferably 50 mol% or more, more preferably 65 mol% or more, and further preferably 80 mol% or more.
Other monomers may be copolymerized in PVA, and a carboxylic acid-containing polymer is effective as a copolymerization component to improve liquid absorption, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid. , Fumaric acid or anhydrides of these unsaturated dibasic acids (for example, maleic anhydride, itaconic anhydride, etc.). Also usable are ethylene, vinyl acetate, vinylamine, acrylamide, vinyl pivalate, sulfonic acid-containing vinyl compounds, and the like. From the viewpoint of practical mechanical performance, it is preferable that the vinyl alcohol unit is a polymer containing 70 mol% or more of all the constituent units.

The polymer constituting the nanofiber may be a cellulosic polymer. Cellulose is suitable because it is hydrophilic and is well-familiar with the alkaline electrolyte, and further swells with the alkaline electrolyte, so that many electrolytes can be retained. As a method for obtaining nanofibers from a cellulose-based polymer, a method for obtaining nanofibers by dissolving cellulose in a solvent such as N-methylmorpholine-N-oxide, or a cellulose derivative nanofiber by dissolving a cellulose derivative in an organic solvent. Any method such as a method for obtaining a nanofiber by hydrolyzing it can be suitably obtained.
Although the polymerization degree of the cellulose used in this invention is not specifically limited, It is preferable that it is 100-2000, More preferably, it is 200-1500, More preferably, it is 300-1200. When the degree of polymerization is less than 100, the strength of the obtained nanofiber itself may be very weak. On the other hand, when the degree of polymerization exceeds 2000, the solubility in a solvent becomes insufficient, and the spinnability may be poor. In addition, the polymerization degree of the cellulose as used in the field of this invention is an average polymerization degree measured using a Oken type viscometer based on JISP8101-1994.

Examples of the cellulose derivative include cellulose ester and cellulose ether. Specific examples include cellulose acetate such as cellulose diacetate and cellulose triacetate, cellulose nitrate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, water-insoluble low-substituted carboxymethyl cellulose, starch, and the like.
Among these, the cellulose ester is saponified in an alkaline electrolyte, and free acid is generated in the electrolyte to be an impurity. Therefore, the cellulose ester may be subjected to alkali saponification before being incorporated into a battery to be cellulose.
The polymerization degree and substitution degree of these cellulose derivatives are not particularly limited.

Further, the polymer constituting the nanofiber may be a crosslinked superabsorbent polymer in addition to the PVA polymer and the cellulose polymer described above.
Since the polymer is hydrophilic, it can be used well with an alkaline electrolyte, and further, since it swells with an alkaline electrolyte, it can hold a large amount of electrolyte, which is preferable.
The cross-linked superabsorbent polymer used in the present invention is not particularly limited as long as it has a carboxyl group in the molecule or at the molecular end, is a cross-linked polymer and has excellent alkali resistance. Examples of the crosslinked superabsorbent polymer having a carboxyl group include PVA, carboxymethylcellulose, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polycrotonic acid, polycrotonate, and maleic anhydride copolymer. (Isobutyl-maleic anhydride copolymer, methyl vinyl ether and maleic anhydride copolymer, styrene-maleic anhydride copolymer, polyacryl-maleic anhydride copolymer) and the like are preferably crosslinked with a crosslinking agent. Can be used. The molecular weight of these cross-linked superabsorbent polymers is not particularly limited, but the average molecular weight is preferably in the range of 1,000 to 1,000,000. From the viewpoint of spinnability, 5,000 to 800,000 is more preferably used.
Moreover, as a crosslinking agent, the water-soluble epoxy resin represented by glycerol polyglycidyl ether, polyethyleneimine, etc. are mentioned. These crosslinking agents can be added to the above-mentioned crosslinked superabsorbent polymer having a carboxyl group, and the crosslinked superabsorbent polymer can be crosslinked by heating or the like.

Next, also in the dry nonwoven fabric laminated | stacked with a nanofiber by this invention, it needs to be comprised with an alkali-resistant polymer.
As the polymer excellent in alkali resistance constituting the dry nonwoven fabric, a polymer similar to the nanofiber is preferably used.
Fibers composed of polymers with excellent alkali resistance include PVA fibers, cellulose fibers, fluorine fibers, polyvinyl chloride fibers, polyamide fibers, polyethylene fibers, polypropylene fibers, polyimide fibers, polybenzimidazole fibers. , Polyarylate fibers, polyethylene sulfide fibers and the like, and one or more selected from these can be used.

  In the present invention, the polymer constituting the dry nonwoven fabric is preferably PVA. PVA is suitable because it has good alkali resistance and is hydrophilic, so that it can be used with an alkaline electrolyte. The PVA fiber constituting the dry nonwoven fabric does not need to be composed only of PVA, and may contain other polymers, and may be a composite spun fiber or a mixed spun fiber (sea island fiber) with another polymer. It does not matter. From the standpoint of electrolyte absorption, it is preferable to use a PVA fiber containing PVA in an amount of 30% by mass or more, particularly 50% by mass or more, and more preferably 80% by mass or more. The fineness of the fiber is preferably 3.3 dtex or less, particularly 2.2 dtex or less, from the viewpoint of separation properties and thinning. The fiber length may be appropriately set according to the single fiber fineness and the non-woven fabric production method.

  In the present invention, the polymer constituting the dry nonwoven fabric may be a cellulosic polymer. Cellulose is suitable because it is hydrophilic and is well-familiar with the alkaline electrolyte, and further swells with the alkaline electrolyte, so that many electrolytes can be retained. Examples of the alkali-resistant cellulose fibers constituting the dry nonwoven fabric include rayon fibers (including polynosic rayon fibers and organic solvent-based cellulose fibers), acetate fibers, and mercerized natural pulp (wood pulp, cotton linter pulp, hemp pulp, etc.) It is done. However, if the content of the alkali-resistant cellulose fiber in the nonwoven fabric exceeds 90% by mass, the stiffness of the separator is weakened, and the separator itself buckles due to vibration / dropping impact during battery transportation and carrying, causing an internal short circuit. Since there exists a possibility, it is preferable that content of the alkali-resistant cellulose fiber in a nonwoven fabric is less than 90 mass%.

In the present invention, the polymer constituting the dry nonwoven fabric may be a crosslinked superabsorbent polymer. Since the polymer is hydrophilic, it is well-familiar with the alkaline electrolyte, and further swells with the alkaline electrolyte, so that a large amount of the electrolyte can be retained, which is preferable. Examples of the alkali-resistant crosslinked superabsorbent fibers constituting the dry nonwoven fabric include PVA crosslinked superabsorbent fibers, acrylic crosslinked superabsorbent fibers, polyethylene glycol crosslinked superabsorbent fibers, and any of these can be suitably used. It is.
However, if the content of the alkali-resistant crosslinked superabsorbent fiber in the nonwoven fabric exceeds 70% by mass, the stiffness of the separator becomes weak, and the separator itself buckles due to the impact of vibration / dropping when the battery is transported or carried. Since there is a possibility of causing a short circuit, the content of the alkali-resistant crosslinked superabsorbent fiber in the nonwoven fabric is preferably less than 70% by mass.

Next, production of the nanofiber of the present invention will be described. First, a solution dissolved in a solvent capable of dissolving the alkali resistant polymer is prepared. As a solvent, water, an organic solvent, etc. can be used without problems. A solution obtained by dissolving an alkali-resistant polymer in this solvent and uniformly removing the granular gel is used as a spinning dope.
Next, an alkali-resistant polymer is laminated or combined on the base sheet by the electrospinning method using the above spinning solution. There is no particular limitation on the method of electrostatic spinning, and a method of depositing nanofibers on the grounded counter electrode side by applying a high voltage to a conductive member capable of supplying a spinning solution is used. As a result, the spinning stock solution discharged from the stock solution supply section is charged and split, and then the fiber is continuously drawn from one point of the droplet by the electric field, and a large number of the divided fibers are diffused. Even when the concentration of the polymer is 10% or less, the solvent is easily dried at the stage of fiber formation and thinning, and is deposited on a collecting belt or sheet installed several cm to several tens cm away from the stock solution supply unit. The semi-dried fibers are finely agglomerated with the deposition to prevent the movement between the fibers, and the new fine fibers are sequentially deposited to obtain a dense sheet.

Hereinafter, the nanofiber composite method of the present invention will be briefly described with reference to the apparatus shown in FIG. In FIG. 1, a spinning stock solution in which an alkali-resistant polymer is dissolved is metered by a metering pump 1, distributed by a distribution rectifying block 2 so as to have a uniform pressure and amount, and sent to a base unit 3. In the base part, a base 4 that is protruded for each hole in the shape of a hollow needle is attached, and electricity is prevented from leaking to the whole base part 3 by an electrical insulating part 5. A plurality of protruding caps 4 made of a conductive material are mounted vertically downward in parallel with a direction perpendicular to the traveling direction of the forming sheet take-up device 7 formed of an endless conveyor, and one output terminal of a DC high voltage generating power source is connected to the protruding base 4. The protruding caps 4 are attached to the caps 4 and can be applied by conducting wires. The endless conveyor of the forming sheet take-up device is provided with a grounded conductive member 8 so that the applied potential can be neutralized. The spinning dope fed from the base part 3 to the projecting base 4 is charged and split, and then the fiber is continuously drawn from one point of the droplet by the electric field, and a large number of the split fibers are diffused and formed into a semi-dry state. It accumulates on the conductive member attached to the take-up device 7, the sticking progresses, is moved by the sheet and the take-up device, and along with the movement, the fine fibers of the next projecting cap are deposited, A dense and uniform sheet-like material is formed while repeating.
The fiber diameter of the nanofiber produced at this time is the conditions such as the concentration of the alkali-resistant polymer stock solution, the distance between the base 4 and the formed sheet take-up device 7 (distance between the electrodes), the voltage applied to the base 4, etc. Can be controlled to a predetermined fiber diameter.

  Next, the manufacturing method of the dry nonwoven fabric used for the base material laminated | stacked with a nanofiber in the battery separator of this invention is demonstrated. The production method of the dry nonwoven fabric is not particularly limited, and any of a spunbond method, a melt blown method, a spunlace method, a thermal bond method, a chemical bond method, an airlaid method, a needle punch method, and the like can be suitably applied. It is also possible to apply a melt or solution of an alkali-resistant polymer to the nonwoven fabric. Although the film cannot satisfy the air permeability which is one of the preferred conditions of the present invention, the coating weight is not limited as long as the air permeability as a laminate is satisfied in the coating method. .

Next, nanofibers are laminated on the obtained nonwoven fabric as described above. The amount to be laminated (basis weight) is 0.1 to 10.0 g / m ² , preferably 0.2 to 5.0 g / m ² . When the basis weight of the nanofiber is less than 0.1 g / m ² , prevention of an internal short circuit by the needle-like dendrite becomes insufficient. On the other hand, when the basis weight of the nanofiber exceeds 10.0 g / m ² , the impedance (resistance value) of the separator itself becomes high and the battery performance is inferior. Moreover, since the separator after battery performance electrolyte absorption becomes thick and the occupancy rate of the separator inside a battery increases, the capacity | capacitance of a positive / negative electrode agent is restrict | limited, and the discharge performance of heavy discharge cannot be obtained.
Moreover, the said separator can also be adjusted to the target thickness by a hot press or a cold press as needed.

In the separator for an alkaline battery of the present invention, the air permeability is preferably 0.1 to 10.0 cc / cm ² / sec, more preferably as an index of the void range in which internal short circuit due to dendrites can be more highly prevented. 1.0 to 5.0 cc / cm ² / sec. When the air permeability is 10.0 cc / cm ² / sec or more, the air gap becomes too large to prevent an internal short circuit due to the zinc oxide needle-like dendrite, and to prevent a decrease in battery performance and battery life. I can't. When the air permeability is less than 0.1 cc / cm ² / sec, the ion permeability is poor and the internal resistance is improved, so that the battery performance cannot be satisfied.

  In addition, the alkaline battery separator of the present invention is also characterized in that the fibers themselves are highly absorbent. The improvement in battery life depends on the liquid absorption performance of the fibers themselves constituting the sheet. Even if the liquid retention amount of the sheet itself is high, if the fiber itself is not retained, partial liquid erosion is likely to occur, and this portion causes an internal short circuit. This index can be determined by the fiber absorption, and a range in which this value is 1.0 to 3.0 g / g is preferable, and 1.2 to 2.0 g / g is more preferable. When the amount is 1.0 g / g or less, the liquid absorption amount of the fibers constituting the sheet is insufficient, and the battery life is likely to be shortened due to liquid drainage. On the other hand, if it is 3.0 g / g or more, the thickness after liquid absorption is increased and the amount of local material is limited, resulting in a decrease in battery performance.

  In the alkaline battery separator of the present invention, the fiber absorption amount of the entire laminated sheet is greatly affected, but the fiber absorption amount of the nanofiber layer itself also greatly affects the battery performance. The fiber absorption amount is preferably 2.0 to 20.0 g / g, more preferably 4.0 to 15.0 g / g. If it is less than 2.0 g / g, the electrolyte solution held by the nanofiber layer itself is drained, resulting in an increase in internal resistance. When it is 20.0 g / g or more, the swelling of the fibers is too large, and as a result, the voids of the sheet are blocked, the internal resistance is improved, and sufficient battery performance cannot be obtained.

  As described above, in order to improve the performance and extend the life of the battery, it is necessary to increase the capacity of the positive / negative electrode agent and reduce the occupancy rate of the separator. From this point of view, the thickness of the separator after absorbing the electrolyte is preferably 0.08 to 0.300 mm, more preferably 0.08 to 0.250 mm.

  Further, in order to cause a sufficient electromotive reaction, it is preferable that the ion conductivity is good and the separator itself has a small impedance (resistance value). In particular, in order to prolong the battery life, it is preferable that the separator itself retains the electrolytic solution even when the electrolytic solution is low at the end of the battery reaction and has a low impedance. As a standard for battery life, it is preferable that the electric resistance value (particularly in the state of running out of liquid) be 3.5Ω or less, and more preferably 0.5 to 3.0Ω.

  By using the separator for alkaline batteries of the present invention, a high-performance and long-life alkaline battery that can withstand heavy load discharge performance can be obtained. The shape of the separator in the alkaline battery is not particularly limited, and examples thereof include a cross trip (cylindrical bottomed cylindrical separator), a round strip (cylindrical cylindrical separator), and a spiral (spiral separator).

  As the electrode material constituting the alkaline battery, zinc oxide can be used as the negative electrode active material, and a gel-like material composed of 40% by mass potassium hydroxide aqueous solution, gelling agent, and zinc powder can be used as the electrolyte. It is desirable to use zinc powder to which mercury, cadmium and lead are not added. In particular, a zinc alloy powder containing at least one selected from bismuth, indium, calcium and aluminum is preferably used in the zinc powder. On the other hand, a positive electrode mixture mainly composed of manganese dioxide and graphite can be used for the positive electrode. Moreover, it is preferable to use the positive electrode mixture containing the nickel oxyhydroxide used for the alkaline battery excellent in a heavy load discharge performance. In addition, from the viewpoint of securing the strong load discharge characteristics and the superiority of the storage performance, a more preferable content ratio of manganese dioxide and nickel oxyhydroxide is manganese dioxide: nickel oxyhydroxide = 80: 20 to 40:60 (mass Part).

  The separator for alkaline batteries of the present invention can also be used as a bottom paper for cylindrical batteries. By absorbing and swelling the electrolyte and filling the pores of the non-woven fabric, it is possible to ensure shielding and to maintain high liquid absorption performance for a long time, and currently used bottom paper (paper / cellophane / paper) ) And the alkaline battery separator of the present invention can be used as a base paper without any problem.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples. In the following examples, each physical property value is measured by the following method.

[Basis weight g / m ² ]
Measured according to JIS P8124 “Measuring basis weight of paper”.
[Thickness mm]
After 5 places of the obtained separator were allowed to stand in a standard environment (20 ° C. × 65% RH) for 4 hours or longer, measurement was performed with PEACOCK Dial-Thickness Gauge H Type (φ10 mm × 180 g / cm ² ).

[Air permeability cc / cm ² / sec]
It was measured with a Fragil air permeability tester (manufactured by Toyo Seiki Seisakusho).
[Fiber absorption, total absorption g / g]
A 50 mm × 50 mm sample was immersed in a 35% KOH aqueous solution (20 ° C.) for 30 minutes under a bath ratio of 1: 100, drained for 30 seconds, and then subjected to centrifugal dehydration (3,000 rpm × 10 minutes). Measured and calculated by the following formula.
Total liquid absorption (g / g) = (W2-W1) / W1
Absorbed amount of fiber (g / g) = (W3-W1) / W1
W1 = mass of sample W2 = mass after draining W3 = mass after centrifugal dehydration * For the fiber absorption of the nanofiber layer, the fiber absorption of the base material is obtained and the fiber absorption of the laminated sheet is obtained. Calculated by subtracting from the amount.

[Impedance (resistance value)]
The sample was immersed in a 35% KOH aqueous solution (20 ° C.) for 30 minutes in the same manner as the measurement of the total liquid absorption and fiber absorption, and the liquid was sufficiently retained (30 seconds after draining). The same sample was made into a liquid-run state after centrifugal dehydration (3,000 rpm × 10 minutes), and an impedance measuring instrument (“KC-547 LCR METER” manufactured by Kuniyo Denki Kogyo Co., Ltd.) in a measurement atmosphere of 20 ° C. × 65% RH. The thickness was measured to be constant (0.100 mm).

[Battery performance evaluation]
As a battery performance evaluation method, AA-size alkaline batteries were prepared, and the discharge performance was compared immediately after assembly and after high-temperature storage (storage at 80 ° C. for 3 days). The discharge performance was evaluated based on the discharge time required to reach a final voltage of 0.9 V when intermittent discharge was performed for 5 minutes each day at a load of 3.9Ω at an environmental temperature of 20 ° C. What evaluated the performance about the alkaline battery which incorporated the separator and used the manganese dioxide and graphite mixture for the positive electrode agent, when the discharge time immediately after the assembly and after high temperature storage in the battery obtained in Comparative Example 7 was 100 It was expressed as a relative value. If the relative value of the discharge time immediately after assembly and after storage at high temperature is 100 or more, it is judged that the product has a long life, does not short-circuit internally, and is not oxidized and deteriorated. If it was less than 100, it was judged as x.
The battery manufacturing method will be described in detail in Example 1.

[Example 1]
(1) 70% by mass of PVA fiber (Kuraray “WN7”; 1.7 dtex × 3 mm) and 30% by mass of PVA superabsorbent fiber (Kuraray “QV4L”; 2.2 dtex × 51 mm) After forming into a web, an embossed nonwoven fabric is prepared, calendered at 170 ° C., and a dry nonwoven fabric base material having a basis weight of 29.4 g / m ² and a 35% KOH aqueous solution fiber absorption of 1.1 g / g. Got.
(2) Next, a nanofiber layer is formed. First, a PVA polymer (“KM-118” manufactured by Kuraray Co., Ltd .; polymerization degree 1780, saponification degree 98 mol%, maleic acid 2 mol% modified) was added to water so as to be 10% by mass, and stirred and dissolved at 90 ° C. Then, the completely dissolved solution was cooled to room temperature to obtain a spinning dope. Using the obtained spinning dope, electrostatic spinning was performed with the spinning device of FIG. A needle having an inner diameter of 0.9 mm was used as the base 4. Moreover, the distance (distance between poles) between the die 4 and the formed sheet take-up device 7 was 8 cm. Furthermore, the wet nonwoven fabric base material obtained in the above (1) was wound around the forming sheet take-up device 7. Next, the conveyor speed is 0.1 m / min, the stock solution is extruded from the die at a predetermined supply amount, a 20 kV applied voltage is applied to the die, and a nanofiber having a fiber diameter of 250 nm is applied to the nonwoven fabric on the cylinder at a basis weight of 1.0 g / m. ^Two layers were laminated. Table 1 shows the performance of the obtained laminated sheet.

(3) Further, for the battery evaluation, a positive electrode agent composed of 94.3% by mass of manganese dioxide, 4.8% by mass of graphite powder, and 0.93% by mass of 40% by mass of KOH aqueous solution as an electrolyte was uniformly mixed with a mixer. Mixed. Manganese dioxide was classified in a particle size range of 20 to 50 μm, and graphite powder was classified in a range of particle size in the range of 10 to 25 μm.
Next, the positive electrode agent prepared by the above method was compression molded into short cylindrical pellets.
(4) On the other hand, as the negative electrode mixture, 1% by mass of sodium polyacrylate as a gelling agent, 33% by mass of 40% by mass of KOH aqueous solution, 66% by mass of zinc alloy powder, and the silicon element concentration with respect to the zinc powder Thus, a gelled negative electrode agent to which potassium silicate was added so as to be 50 ppm was used. As the zinc alloy powder, a zinc powder having 200% by mass of bismuth, 500% by mass of indium, and 30% by mass of aluminum was used.
(5) Using the obtained positive electrode mixture pellet, gelled negative electrode mixture, and the obtained separator and bottom paper (“CSBI” manufactured by Kuraray Co., Ltd.), the separator is a round strip (cylindrical cylindrical separator) type. The battery was assembled to have a structure and a discharge test was conducted. The results are shown in Table 1.

[Example 2]
A sheet was obtained under the same conditions as in Example 1 except that the nanofiber lamination amount (basis weight) was changed to 0.4 g / m ² . The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1.

[Example 3]
The nanofiber layer was formed under the same conditions as in Example 1 except that cellulose acetate (manufactured by Wako Pure Chemical Industries, cellulose diacetate) was charged into dimethylformamide (DMF) so as to be 10% by mass and dissolved. Electrospinning was carried out, and further, cellulose acetate was saponified by alkali saponification of cellulose acetate by dipping in 1N NaOH methanol solution at 50 ° C. for 30 minutes. In addition, the same dry type nonwoven fabric as Example 1 was used for the base material. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1.

[Example 4]
As the formation of the nanofiber layer, polyacrylic acid (“Julimer AC-10LHP” manufactured by Nippon Pure Chemical Co., Ltd .; average molecular weight 250,000) is charged and dissolved in water so as to be 10% by mass, and this is used as a crosslinking agent. Polyethyleneimine (“Epomin SP-200” manufactured by Nippon Shokubai Co., Ltd .; molecular weight 10,000) added to 1% by mass of polyacrylic acid and dissolved is used as a spinning dope, and after laminating nanofibers, A laminated sheet was obtained using the same dry nonwoven fabric substrate as in Example 1 except that curing was performed at 200 ° C. for 1 minute for the purpose of crosslinking. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1.

[Example 5]
As a dry nonwoven fabric substrate, an isobutyl-maleic acid copolymer (“Isoban-10” manufactured by Kuraray Co., Ltd .; average molecular weight 160,000) was used, and polyethyleneimine (“Epomin SP-” manufactured by Nippon Shokubai Co., Ltd.) was used as a crosslinking agent. 200 ”; molecular weight 10,000) with respect to polyacrylic acid, and an aqueous potassium silicate solution (so that potassium silicate is contained at 5.0 × 10 ⁻³ mg / cm ² per sheet unit area). What was added with “Oka Seal” manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied to one side of a polypropylene spunbonded nonwoven fabric (“Stratec PP” manufactured by Idemitsu Unitech Co., Ltd.) with a knife coater, and the resistance was 9.9 g / m ² . Alkali alkaline super absorbent polymer was deposited. Then, after drying with a hot air through dryer, curing was performed with a hot air through dryer at 200 ° C. for 1 minute. Next, the thickness was adjusted with a calender to obtain a dry nonwoven fabric substrate with a basis weight of 40.4 g / m ² and a 35% KOH aqueous solution fiber absorption of 1.4 g / g. Thus, lamination | stacking of the nanofiber on the dry type nonwoven fabric base material obtained was performed on the conditions similar to Example 1, and the lamination sheet was obtained. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1.

[Example 6]
A laminated sheet was obtained under the same conditions as in Example 5 except that a polypropylene mesh ("PROPYLEX PP100-149" manufactured by Swiss SEFAR) was used instead of the polypropylene spunbonded nonwoven fabric. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1.

[Example 7]
As a dry nonwoven fabric substrate, rayon fiber [Daiwabo Co., Ltd. “Corona”; 1.7 dtex × 40 mm] 80 mass% and PVA fiber [Kuraray Co., Ltd. “WN7”; 1.7 dtex × 38 mm] 20 mass % Was used as a web, and a spunlace nonwoven fabric was prepared and calendered at 170 ° C. to obtain a dry nonwoven fabric having a basis weight of 30.4 g / m ² and a 35% KOH aqueous fiber absorption of 1.8 g / g. .
A laminated sheet was obtained under the same conditions as in Example 1 except for the above. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1.

[Comparative Example 1]
In Example 1, a laminated sheet was obtained under the same conditions as in Example 1 except that the dry nonwoven fabric base material was 100% by mass of PVA fiber (“WN7” manufactured by Kuraray Co., Ltd.). The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1. The battery was in an end-of-discharge state because the fiber absorption of the laminated sheet was small. In addition, the resistance value after draining was also increased, and the battery life was short in actual battery evaluation.

[Comparative Example 2]
In Example 1, a sheet was obtained under the same conditions as in Example 1 except that the spinning concentration of nanofibers was 14% by mass. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1. Although the obtained laminated sheet satisfies the liquid absorption amount of the fiber, the fiber is thick, which is an index of the tendency to prevent internal short circuit, the air permeability is large, and good results are not obtained even in actual battery performance evaluation It was.

[Comparative Example 3]
In Example 5, a laminated sheet was obtained under the same conditions except that the dry nonwoven fabric base material was only a polypropylene spunbond nonwoven fabric. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1. The battery was in an end-of-discharge state because the fiber absorption of the laminated sheet was small. In addition, the resistance value after draining was also increased, and the battery life was short in actual battery evaluation.

[Comparative Example 4]
In Example 1, a laminated sheet was obtained under the same conditions as in Example 1 except that a PVA film (“Kuraray S” manufactured by Kuraray Co., Ltd.) was used instead of the dry nonwoven fabric. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1. Since the fiber absorption of the laminated sheet was small, the battery discharge was in the final state. High resistance was also observed in the resistance value after withering.

[Comparative Example 5]
In Example 1, as a nanofiber spinning dope, polyester resin (“Kurapet KS760K” manufactured by Kuraray Co., Ltd.) was stirred and dissolved in HFIP at 30 ° C. so as to be 10% by mass, and the completely dissolved solution was cooled to room temperature. Thus, a sheet was obtained under the same conditions as in Example 1 except that a spinning dope was obtained. The performance of the obtained laminated sheet and the results of battery performance evaluation are shown in Table 1. Although there was no problem in particular in the results of Table 1, in the battery performance evaluation, the life was short. This is presumably because the polyester nanofibers were hydrolyzed in the alkaline electrolyte, so that the gaps in the separator became large and internal short circuit due to zinc oxide needle-shaped dendrites could not be prevented.

[Comparative Example 6]
In Example 1, a sheet was obtained under the same conditions as in Example 1 except that the nanofiber was not coated. Table 1 shows the performance of the obtained sheet and the results of battery performance evaluation. Although the obtained sheet satisfied the liquid absorption of the fiber, the air permeability, which is an index of the tendency to prevent internal short circuit, was large, and good results were not obtained even in actual battery performance evaluation.

[Comparative Example 7]
PVA fiber (“VPB103 × 3” manufactured by Kuraray Co., Ltd .; 1.1 dtex × 3 mm) 35% by mass as the main fiber, organic solvent rayon fiber (“Tencel” manufactured by Lenzing Co., Ltd.); 1.7 dtex × 2 mm using a high-speed disintegrator 50% by mass of CSF = 300 ml) and 15% by mass of PVA-based binder fiber (“VPB105-1” manufactured by Kuraray Co., Ltd .; 1.1 dtex × 3 mm) are mixed, and this is a short net-circle net paper. Two-layer paper making was performed with a machine and dried with a Yankee type dryer to obtain a wet nonwoven fabric substrate having a basis weight of 36.8 g / m ² and a thickness of 0.13 mm.
Evaluation was made without laminating nanofibers on this wet nonwoven fabric substrate, but the liquid absorption amount was secured, but the air permeability was not high enough to prevent internal short circuit. The performance and battery performance evaluation results are shown in Table 1.

  According to the present invention, the electrolyte absorbability is increased, the electrolyte is retained for a long time, is not easily subject to oxidative degradation due to the positive electrode mixture, and further, the internal short circuit is prevented by suppressing the growth of dendrite, and the separator itself Therefore, it is possible to obtain a battery separator that can increase the capacity of the positive and negative electrode mixture in the battery by suppressing the thickness after absorbing the electrolyte.

The schematic diagram which shows the apparatus which manufactures the nanofiber laminated | stacked or combined with the base material which consists of a nonwoven fabric.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gear pump 2 Distribution rectification block 3 Base part 4 Base 5 Electrical insulation part 6 DC high voltage generation power supply 7 Form sheet take-up device 8 Conductive member

Claims (11)

  A nanofiber made of an alkali-resistant polymer having a fiber diameter of 10 to 1000 nm and a dry nonwoven fabric composed of an alkali-resistant polymer are laminated and integrated, and the laminated sheet is impregnated with a 35% KOH aqueous solution. An alkaline battery separator having a total liquid absorption of 5.0 to 12.0 g / g.   The alkaline battery separator according to claim 1, wherein the nanofiber is made of a polyvinyl alcohol-based polymer.   The alkaline battery separator according to claim 1, wherein the nanofiber is made of a cellulose polymer.   The alkaline battery separator according to claim 1, wherein the nanofiber is made of a crosslinked superabsorbent polymer.   The alkaline battery separator according to any one of claims 1 to 4, wherein a part of the alkali-resistant polymer constituting the dry nonwoven fabric is a polyvinyl alcohol-based polymer.   The alkaline battery separator according to any one of claims 1 to 4, wherein a part of the alkali-resistant polymer constituting the dry nonwoven fabric is a cellulosic polymer.   The alkaline battery separator according to any one of claims 1 to 4, wherein a part of the alkali-resistant polymer constituting the dry nonwoven fabric is a crosslinked superabsorbent polymer. The laminated and integrated sheet has an air permeability of 0.1 to 10.0 cc / cm ² / sec, and a fiber absorption amount when impregnated with 35% KOH aqueous solution is 1.0 to 3.0 g / g. Item 8. The separator for an alkaline battery according to any one of Items 1 to 7. Alkaline battery separator according to any one of claims 1 to 8 basis weight of the laminated integrated nanofibers is 0.1~10.0g / ^{m 2.}   (A) A step of preparing a solution in which a polymer is dissolved in a solvent capable of dissolving the polymer, (B) A nanofiber is laminated or combined with a base fabric by an electrostatic spinning method using the solution. The separator for alkaline batteries in any one of Claims 1-9 characterized by the above-mentioned.   The battery using the separator for alkaline batteries in any one of Claims 1-10.

Images