The present invention, relates to (i) a method for producing a porous slit separator to be used for a battery such as a lithium-ion secondary battery, (ii) a method for producing a separator roll, which method employs the method for producing the porous slit separator, (iii) a method for slitting a separator, and (iv) a separator slitting apparatus.
A battery separator needs to be produced so as to have a width (hereinafter, referred to as “product width”) that is suitable for a battery to be produced with the use of the separator. However, it is not efficient to produce a separator having such a product width at the time of production. Therefore, it is general practice to prepare a separator original sheet having a wide width, and then to simultaneously produce, by slitting the separator original sheet, a plurality of separators each having the product width.
Patent Literature 1 discloses a spot-type carbon dioxide laser cutting device as a device to slit a separator. Patent Literature 1 teaches using (i) a carbon dioxide laser oscillation unit and (ii) a mirror(s) for bending a laser beam (see paragraph [0050]).
Patent Literature 2 discloses a method for slitting a separator, which method employs a configuration in which a prescribed relationship is made between an angle between a razor blade and the separator and (ii) a thickness of the separator. Patent Literature 1 teaches that the configuration of Patent Literature 2 makes it unlikely that the separator would have pores and tears (see paragraph [0030]).
Note that a separator before being slit is referred to as “original sheet”. Note also that a separator(s) after being slit is referred to as “slit separator”.
[Patent Literature 1]
Japanese Patent Application Publication Tokukai No. 2013-119094 (Publication date: Jun. 17, 2013)
[Patent Literature 2]
Japanese Patent Application Publication Tokukai No. 2002-273684 (Publication date: Sep. 25, 2002)
However, the device disclosed in Patent Literature 1 requires including (i) the carbon dioxide laser oscillation unit and (ii) a mirror(s) for bending a laser beam. This causes the device to be large in size. The mirror, in particular, is required to be provided at each position at which the original sheet is slit. This makes it more difficult to use the device with a larger number of slit separators into which the original sheet is to be slit.
It can be said that the method disclosed in Patent Literature 2 can be used relatively easily even in a case where there is an increase in the number of slit separators into which the original sheet is slit. However, quality of a slit separator is not radically affected by (i) the angle between the razor blade and the separator or (ii) the thickness of the separator. Therefore, a good-quality slit separator is not necessarily obtained by use of the method of Patent Literature 2.
The original sheet is slit, by a plurality of slitting blades aligned in a width direction of the original sheet. However, Patent Literatures 1 and 2 do not teach a configuration for obtaining a good-quality slit separator with vise of a plurality of slitting blades.
The present invention has been made in view of the problem, and it is an object of the present invention to provide (i) a method for producing a slit separator, and (ii) a method for producing a separator roll, each of which method allows a good-quality slit separator and a good-quality separator roll to be obtained.
In order to attain the object, a slit separator production method in accordance with Aspect 1 of the present invention includes: a conveying step of conveying a battery separator original sheet which is porous; and a first slitting step of slitting the battery separator original sheet by causing a plurality of slitting blades to cut into the battery separator original sheet such that a plurality of slitting blade edge angles in a tangent plane, on which a slitting position is in contact with the battery separator original sheet, are substantially identical with each other.
A separator roll production method in accordance with Aspect 2 of the present invention includes: each of the steps recited in the slit separator production method; and a winding step of winding, around a core, a separator obtained by slitting the battery separator original sheet.
Each of the aspects of the present invention brings about such an effect that it is possible to obtain, all at once, (i) a plurality of good-quality slit separators having a small amount of fullness at a slit part thereof and (ii) a good-quality separator roll having a side end surface on which there is a small amount of fuzziness.
[Common Configuration]
The following discusses in order a lithium-ion secondary battery, a separator, a heat resistant separator, a method for producing the heat resistant separator, a slitting apparatus, and a cutting device which are common to Embodiments discussed late.
(Lithium-Ion Secondary Battery)
A nonaqueous electrolyte secondary battery, typically, a lithium-ion secondary battery has a high energy density, and therefore, currently widely used not only as batteries for use in devices such as personal computers, mobile phones, and mobile information terminals, and for use in moving bodies such as automobiles and airplanes, but also as stationary batteries contributing to stable power supply.
As illustrated in
(Separator)
The separator 12 is provided so as to be sandwiched between the cathode 11 which is a positive electrode of the lithium-ion secondary battery 1 and the anode 13 which is a negative electrode of the lithium-ion secondary battery 1. The separator 12 is a porous film that separates the cathode 11 and the anode 13, allowing lithium ions to move between the cathode 11 and the anode 13. The separator 12 contains, for example, polyolefin such as polyethylene or polypropylene as a material.
As illustrated in (a) of
However, there are, for example, cases in which the temperature of the lithium-ion secondary battery 1 rises due to excessive charging of the lithium-ion secondary battery 1, a high current caused by short-circuiting of the external device, or the like. In such cases, the separator 12 melts or softens and the pores P are blocked as illustrated in (b) of
However, in a case where a temperature of the lithium-ion secondary battery 1 sharply rises, the separator 12 suddenly shrinks. In this case, as illustrated in (c) of
(Heat Resistant Separator)
As illustrated in (a) of
As illustrated in (b) of
(Production Steps of the Heat Resistant Separator)
How to produce the heat resistant separator of the lithium-ion secondary battery 1 is not specifically limited. The heat resistant separator 12 can be produced by a well-known method. The following discussion assumes a case where the porous film 5 contains polyethylene as a main material. However, even in a case where the porous film 5 contains another material, the similar steps can still be applied to production of the separator 12.
For example, it is possible to employ a method including the steps of first forming a film by adding a plasticizer to a thermoplastic resin, and then removing the plasticizer with an appropriate solvent. For example, in a case where the porous film 5 is made of a polyethylene resin containing ultrahigh molecular weight polyethylene, it is possible to produce the porous film 5 by the following method.
This method includes (1) a kneading step of obtaining a polyethylene resin composition by kneading a ultrahigh molecular weight polyethylene and an inorganic filler such as calcium carbonate, (2) a rolling step of forming a film with the polyethylene resin composition, (3) a removal step of removing the inorganic filler from the film obtained in the step (2), and (4) a stretching step of obtaining the porous film 5 by stretching the film obtained in the step (3).
In the removal step, many fine pores are provided in the film. The fine pores of the film stretched in the stretching step become the above-described pores P. The porous film 5 formed as a result is a polyethylene microporous film having a prescribed thickness and a prescribed air permeability.
Note that in the kneading step, 100 parts by weight of the ultrahigh molecular weight polyethylene, 5 parts by weight to 200 parts by weight of a low-molecular weight polyolefin having a weight-average molecular weight of 10000 or less, and 100 parts by weight to 400 parts by weight of the inorganic filler can be kneaded.
Thereafter, in a coating step, the heat resistant layer 4 is formed on a surface of the porous film 5. For example, on the porous film 5, an aramid/NMP (N-methylpyrrolidone) solution (coating solution) is applied, and thereby, the heat resistant layer 4 that is an aramid heat resistant layer is formed. The heat resistant layer 4 can be provided on only one surface or both surfaces of the porous film 5. Alternatively, for coating, the heat resistant layer 4 can he formed by using a mixed solution containing a filler such as alumina/carboxymethyl cellulose.
A method for coating the porous film 5 with a coating solution is not specifically limited as long as uniform wet coating can be performed by the method. The method can be a conventionally well-known method such as a capillary coating method, a spin coating method, a slit die coating method, a spray coating method, a dip coating method, a roll coating method, a screen printing method, a flexo printing method, a bar coater method, a gravure coater method, or a die coater method. The heat resistant layer 4 has a thickness which can be controlled by (i) a thickness of a coating wet film and (ii) a solid-content concentration in the coating solution.
It is possible to use a resin film, a belt, a metal drum or the like as a support with which the porous film 5 is fixed or transferred in coating.
As described above, it is possible to produce the separator 12 (heat resistant separator) in which the heat resistant layer 4 is laminated on the porous film 5. Thus produced separator is wound on a cylindrical core. Note that a subject to be produced by the above production method is not limited to the heat resistant separator. The above production method does not necessarily include the coating step. In a case where the method includes no coating step, the subject to be produced is a separator including no heat resistant layer.
(Slitting Apparatus)
The heat resistant, separator or the separator including no heat resistant layer (hereinafter, referred to as “separator”) preferably has a width (hereinafter, referred to as “product width”) suitable for application products such as the lithium-ion secondary battery 1. However, for improving productivity, the separator is produced so as to have a width that is equal to or larger than a product width. Then, after having been once produced so as to have a width equal to or larger than the product width, the separator is slit into a separator(s) having the product width.
Note that the “separator width” means a dimension of the separator in a direction perpendicular to a lengthwise direction and a thicknesswise direction of the separator. In the description below, a wide separator having not yet been slit is referred to as an “original sheet” while particularly a separator having been slit is referred to as a “slit separator”. Note also that slitting means to slit the separator in the lengthwise direction (flow direction of the film during production; MD: Machine direction), and that cutting means to slit the separator in a transverse direction (TD). The transverse direction (TD) means a direction which is substantially perpendicular to the lengthwise direction (MD) and the thicknesswise direction of the separator.
As illustrated in (a) of
(Before Slitting)
In the slitting apparatus 6, a cylindrical core c on which the original sheet is wrapped is fit on the wind-off roller 61. As illustrated in (b) of
(After Slitting)
As illustrated in (b) of
(Cutting Device)
As illustrated in (a) and (b) of
The following discusses an embodiment of the present invention with reference to
<Separator Slitting Method>
(Cutting of Original Sheet by Slitting Blade)
As illustrated in (a) of
As illustrated in (b) of
The original sheet S is a separator immediately before being slit by the slitting blades 72.
(Cross-Sectional Angle of Slitting Blade)
As illustrated in (a) of
(Mounting Angle of Slitting Blade)
As illustrated in (a) of
A cross section taken along the line B-B (hereinafter, referred to as “B-B cross section”) is a tangent plane on which a slitting position of the slitting blade 72 in contact with the original sheet S.
(Tangent-Plane Blade Edge Angle of Slitting Blade)
As illustrated in (b) of
(Two-Stage Edge)
As illustrated in (c) of
(Flow of Separator Slitting Method)
As illustrated in (d) of
(Relationship Between (i) Cross-Sectional Angle and Mounting Angle and (ii) Tangent-Plane Blade Edge Angle)
(a) through (d) of
As illustrated in (a) of
(Cross-Sectional Angle and Mounting Angle)
As illustrated in (b) of
z/2=m·tan(θ1/2) Formula (1)
where (i) the point i is a middle point between the points f and h, (ii) a length of a side between the points f and h is z, and (iii) a length of a line segment between the points g and i is m.
As illustrated in (c) of
m/n=sin(θ2) Formula (2)
where a length of a side between the points e and i is n.
(d) of
tan(θ3/2)=(z/2)/n Formula (3).
By substituting the above Formula (1) into the above Formula (3), the following Formula (4) can be obtained:
tan(θ3/2)=(m/n)·tan(θ1/2) Formula (4)
By substituting the above Formula (2) into the above Formula (4), the following Formula (5) can be obtained:
tan(θ3/2)=sin(θ2)·tan(θ1/2) Formula (5)
By modifying the above Formula (5), the following Formula (6) can be obtained:
θ3=2·tan−1(sin(θ2)·tan(θ1/2)) Formula (6)
(Concrete Example of Slitting Blade)
As a slitting blade 72, an industrial precision knife “FBC4019G” manufactured by Kyocera Corporation, for example, can be used. The specifications of FBC4019G are as follows:
The tangent-plane blade edge angle θ3 is an angle at which a slitting blade 72 cuts in an original sheet S when slitting the original sheet S. Therefore, the tangent-plane blade edge angle θ3 largely affects quality of a slit separator. Then, in a case where the tangent-plane blade edge angle θ3 falls within the above-described range α, it is possible to obtain a good-quality slit separator.
The present invention also encompasses a slitting apparatus 6 (see (a) of
(Equivalent Conditions Producing Same Effect)
The cross-sectional angle θ1 and the mounting angle θ2 only need to be in a range of values derived from a relationship represented by the above Formula (5) while the tangent-plane blade edge angle θ3 falls within the range α. In such a case also, it is possible to obtain a good-quality slit separator.
(Effect Obtained by Shape of Slitting Blade)
As has been described, the shape of each of the slitting blades 72 is plane-symmetrical with respect to the plane a which is perpendicular to the original sheet S and to the A-A cross section (see (a) and (b) of
(Slit separator production method, separator roll production method, and use as slitting apparatus)
The present invention also encompasses a slit separator production method including each step involved in the above-described separator slitting method.
The present invention also encompasses a separator roll production method including each step involved in the above-described separator slitting method.
The present invention also encompasses the slitting apparatus 6 (separator slitting apparatus) which realizes the above-described separator slitting method.
(Appearance of Fuzziness)
As illustrated in (a) and (b) of
The above-described “fuzz” occurs on side parts, which are slit parts, of the separator 12. As illustrated in (c) of
(Advantages of Small Amount of Fuzziness)
If the fuzzes 12a are scattered when, for example, the separator 12 is wound off from the separator roll 10, then there is a risk of adversely affecting a battery to be produced by use of the separator 12. In addition, appearances of the separator roll 10 and of the separator 12 are impaired as illustrated in (c) of
The following discusses Embodiment 2 of the present invention with reference to
<<Other Separator Slitting Methods and their Effects>>
(Circular Slitting Blade)
As illustrated in
cos(90°−θ2a)=(1/2)/r Formula (7)
The above Formula (7) can be modified into the following Formula (8):
90°−θ2a=cos−1((1/2)/r) Formula (8)
The above Formula (8) can be modified into the following Formula (9):
θ2a=90°−cos−1((1/2)/r) Formula (9)
(Equivalent Conditions Producing Identical Effect as that of Flat Slitting Blade)
The fact that the entry angle θ2a is formed between the blade edge Ea of the slitting blade 72a and the original sheet S is equivalent to the fact that the mounting angle θ2 is formed between the blade edge E of the above-described slitting blade 72 and the original sheet S. In this case, the A-A cross section shown in
(Slitting by Use of Single-Beveled Slitting Blade)
As illustrated in (a) of
Note that a cross-sectional angle θ1a of a blade edge E of the slitting blade 72b is a half of the cross-sectional angle θ1 of the slitting blades 72.
θ1a=θ1/2 Formula (10)
In addition, as illustrated in (b) of
θ3a=θ3/2 Formula (11)
By substituting the above Formulas (10) and (11) into the above Formula (6), the following Formula (12) can be obtained:
θ3a=tan−1(sin(θ2)·tan(θ1a)) Formula (12)
By use of the above Formula (12), the tangent-plane blade edge angle 83a of the slitting blade 72b, which is a single-beveled blade, can also be calculated as is the case of the slitting blades 72 which is a double-beveled blade.
(Slitting on Roller)
As illustrated in
In this case, an entry angle θ2b formed between the slitting blade 72 and the original sheet S being conveyed by the roller 66 can be calculated by use of the following Formula (13):
θ2b=cos−1((r−z) Formula (13)
r: radius of roller 66
By using this angle θ in a manner similar to how the mounting angle θ2 is used, the tangent-plane blade edge angle θ3 can be calculated according to the above Formula (6).
Alternatively, the above-described slitting blade 72b can be used instead of the slitting blade 72. In such a case also, by using the entry angle in a manner similar to how the mounting angle 82 is used, the tangent-plane blade edge angle 83a can be calculated according to the above Formula (12).
It is thus possible to calculate a tangent-plane blade edge angle even in a case of slitting an original sheet S on a roller.
(Slitting by Use of a Pair of Slitting Blades)
As illustrated in
As each of slitting blades 72c, an industrial precision knife “GUBD-09807T45DC15 (cross-sectional angle θ1a of blade edge; 45°)” manufactured by Kyocera Corporation, for example, can be used. As each of slitting blades 72d, an industrial precision knife “GDBD-08005T” manufactured by Kyocera Corporation, for example, can be used.
As illustrated in (a) and (b) of
The slitting blades 72d are each provided with a groove part 72db. The slitting blades 72c, which are upper blades of the pairs of slitting blades 72c and 72d, are each a single-beveled blade. A blade edge Ec of each of the slitting blades 72c is in contact with a corresponding one of side parts 72dc, each of which is part of a side surface of a groove part 72db of a slitting blade 72d.
Note that, according to the law of cosines, the following Formulas (14) to (16), which concern a triangle having points Oc, Od and s shown in
rc
2
+OcOd
2−2·rc·OcOd·cos(θ2ce)=rd2 Formula (14)
rd
2
+OcOd
2−2·rd·OcOd·cos(θ2cd)=rc2 Formula (15)
OcOd=rc+rd−n Formula (16)
OcOd: Length between (i) the point Oc which is a center around which the slitting blade 72c rotates and (ii) the point Od which is a center around which the slitting blade 72d rotates
By modifying the above Formulas (14) to (15), the following Formulas (17) to (18) can be obtained:
θ2cc=cos−1((rc2+OcOd2−rd2)/(2·rc·OcOd)) Formula (17)
θ2cd=cos−1((rd2+OcOd2−rc2)/(2·rc·OcOd)) Formula (18)
By using an entry angle “θ2cc+θ2cd”, which is a sum of said one and the other entry angles θ2cc·θ2cd, in a manner similar to how the mounting angle θ2 is used, it is possible to calculate the tangent-plane blade edge angle θ3a according to the above Formula (12).
It is thus possible to calculate a tangent-plane blade edge angle even in a case of slitting an original sheet S by use of pairs of slitting blades.
The following describes Embodiment 3 of the present invention.
<<Verification of Separator Slitting Method>>
In the following description, a type of separator to be slit, a type of slitting blade (flat blade, circular blade), a cross-sectional shape (double-beveled blade, single-beveled blade) of a slitting blade, a cross-sectional angle θ1 of a blade edge of a slitting blade, and a mounting angle θ2 of the slitting blade are variously changed so as to specifically verify that quality of a slit separator depends on a tangent-plane blade edge angle θ3.
(Conditions in Which to Produce Slitting Film)
<Production of Polyolefin Porous Film>
In this verification, two types of separators are used. These separators are identical to the above-described “heat resistant separator”. Conditions, in which to produce a porous film constituting each of the heat resistant separators, are as follows.
70% by weight of a high molecular weight polyethylene powder (GUR4032 (manufactured by Ticona Corporation)) and 30% by weight of polyethylene wax (FNP-0115 (manufactured by Nippon Seiro Co., Ltd.)) having a weight-average molecular weight of 1000 were prepared. Then, to a total of 100 parts by weight of the high molecular weight polyethylene and the polyethylene wax thus prepared, 0.4 part by weight of antioxidant (Irg1010 (manufactured by Ciba Specialty Chemicals Corporation)), 0.1 part by weight of (P168 (manufactured by Ciba Specialty Chemicals Corporation)), and 1.3 parts by weight of sodium stearate were added. Then, to 100% by volume of a resultant mixture, 38% by volume of calcium carbonate (manufactured by Maruo Calcium Co., Ltd.) having an average par tide size of 0.1 μm was added. A resultant powder, while being a powder, was mixed with the use of a Henschel mixer. Then, the resultant powder was melted and kneaded with the use of a biaxial kneader, so that a polyolefin resin composition was obtained. The polyolefin resin composition was rolled with the use of a parr of rolls each having a surface temperature of 150° C., so that a sheet was produced. The sheet was immersed in a hydrochloric acid aqueous solution (4 mol/L of hydrochloric acid, 0.5% by weight of nonionic surfactant), so that calcium carbonate was removed. Then, a resultant sheet was stretched by a given multiplying factor at 105° C., so that a polyolefin porous film having a thickness of 13.5 μm was obtained.
<Synthesis of Para-Aramid>
Conditions, in which to produce para-aramid for obtaining a heat resistant layer constituting each of the heat resistant separators, are as follows.
Para-aramid (poly (paraphenylene terephthalamide)) was produced with the use of a 3-liter separable flask equipped with a stirring blade, a thermometer, a nitrogen incurrent canal, and a powder addition port. In the flask in a sufficiently dry state, 2200 g of N-methyl-2-pyrrolidone (NMP) was introduced, and then 151.07 g of calcium chloride powder, which had been dried in vacuum at 200° C. for 2 hours, was added. A temperature of the flask was then increased to 100° C., so that calcium chloride was completely dissolved in the NMP. A temperature of a resultant calcium, chloride solution was returned to room temperature, and then 68.23 g of paraphenylene diamine was added to and completely dissolved in the solution. 124.97 g of terephthalic acid dichloride was divided into 10 parts, which were then added at approximately 5-minute intervals to the solution while the solution was maintained at 20° C.±2° C. The solution was matured while being stirred and maintained at 20° C.±2° C. for 1 hour, so that a para-aramid solution having a para-aramid concentration of 6% by weight.
<Production of Heat Resistant Layer-Forming Slurry A>
Conditions, in which, to produce a heat resistant layer-forming slurry A for obtaining the heat resistant layer, are as follows.
To 100 g of the para-aramid solution thus obtained, 243 g of NMP was added, and then a resultant solution was stirred for 60 minutes, so that a para-aramid solution having a para-aramid concentration of 1.75% by weight was obtained. Meanwhile, 6 g of alumina powder (Alumina C (manufactured by Nippon Aerosil Co., Ltd.), absolute specific gravity: 3.2 g/cm3) and 6 g of alumina powder (Advanced Alumina AA-03 (manufactured by Sumitomo Chemical Co., Ltd.), absolute specific gravity: 4.0 g/cm3) were mixed, so that 12 g of an alumina powder mixture was obtained. Then, 12 g of the alumina powder mixture was mixed with the para-aramid solution having a para-aramid concentration of 1.75% by weight, and then a mixture was stirred for 240 minutes, so that an alumina powder-containing para-aramid solution was obtained. Then, the alumina powder-containing para-aramid solution was filtered with the use of a 1000-mesh metal net. Then, to a resultant filtrate, 0.73 g of calcium oxide was added. Then, a resultant mixture was stirred for 240 minutes for neutralization, and was then defoamed under reduced pressure, so that the heat resistant layer-forming slurry A was obtained.
<Production of Laminated Porous Film A>
Conditions, in which to produce one of the above-described two types of separators, are as follows.
A roll (width: 300 mm, length: 300 m) of the polyolefin porous film was attached to a wind-off machine. While the polyolefin porous film was being pulled, the heat resistant layer-forming slurry A was applied to one surface of the polyolefin porous film, so that a laminated porous film A was continuously obtained.
To be specific, NMP was applied to a lower surface of the polyolefin porous film with the use of a micro-gravure coaler, and the heat resistant layer-forming slurry A was applied, in a prescribed thickness, to an upper surface of the polyolefin porous film with the use of a bar coater. Next, the film after being thus coated was allowed to pass through the inside of a constant temperature/humidity chamber (temperature: 50° C., relative humidity: 70%), so that para-aramid was precipitated from the coated film. Then, the film was allowed to pass through a water washing device (device having such a structure that a guide roll is set in a chamber (i) into which ion exchange water is injected at an injection rate of 10 liters/minute and (ii) from which the ion exchange water filling the inside of the chamber is discharged at a rate identical to the injection rate), so that NMP and calcium chloride were removed from the film.
Then, while hot air is blowing at the washed film with the use of a dryer, the film was allowed to pass through a heat roll, so that moisture content was dried and removed. This caused a laminated porous film A, which had a thickness of 17.0 μm and was constituted by laminating a heat resistant layer on one surface of the polyolefin porous film, was obtained.
A plate knife (manufactured by Kyocera Corporation, FBC4019G, blade edge cross-sectional angle: 25°) was attached to a slitting apparatus (manufactured by Hagihara Industries Inc., model: HDF-105S-1000). Then, in accordance with the conditions shown in Table 1, the laminated porous film A was slit while being moved along a roll having a diameter of 80 mm.
<Production of Heat Resistant Layer-Forming Slurry B>
Conditions, in which to produce a heat resistant layer-forming slurry B for obtaining a heat resistant layer to be provided on the other one of the above-described two types of separators, are as follows.
To a medium in which a weight ratio between pure water and isopropyl alcohol was 90:10, carhoxymethyl cellulose (CMC) (1110 (Manufactured by Daicel FineChem Ltd.), absolute specific gravity: 1.6 g/cm3) and alumina powder (AKP3000 (manufactured by Sumitomo Chemical Co., Ltd.), absolute specific gravity: 4.0 g/cm3) were added and mixed at a weight ratio of 3:100 so that a solid content concentration was 28% by weight. Then, a resultant mixture was dispersed under high pressure, so that the resistant layer-forming slurry B was obtained.
<Production of Laminated Porous Film B>
Conditions, in which to produce the other separator, are as follows.
To a non-coated surface of the laminated porous film A, the heat resistant layer-forming slurry B was applied, so that a laminated porous film B was continuously obtained.
To be specific, the non-coated surface of the laminated porous film A was subjected to a corona treatment. Then, the heat resistant layer-forming slurry B was applied, with the use of a gravure coating machine, to the surface which was thus subjected to the corona treatment, and then the surface was dried. This caused a laminated porous film B, which had a thickness of 25.5 μm and was constituted by laminating an aramid heat resistant layer on one surface of the polyolefin porous film and by laminating a heat resistant layer (constituted by an alumina powder) on the other surface of the polyolefin porous film, was obtained.
(Slitting Conditions)
Table 1 shows the verification results indicating that quality of a slit separator (laminated porous film A or B after being slit) depends on a tangent-plane blade edge angle Θ3.
As shown in Table 1, the verification was performed by use of eight examples (Examples 1 through 6, Comparative Examples 1 and 2). In regard to “Example 1” on the first row of Table 1, numerical values provided in columns to the right of the leftmost column indicate numerical values obtained in Example 1. The same principle also applies to the other examples.
“Film type” indicates whether a slit separator is the above-described laminated porous film A or B.
“Blade depth z”, “Cross-sectional angle θ1”, “Mounting angle θ2”, and “Tangent-plane blade edge angle θ3” are as described in the above embodiments.
“Fuzziness amount” indicates an amount of fuzziness that occurred at slit parts of a slit separator. “Grade A” indicates that the -quality of a slit separator is excellent (there is no visible fuzziness). “Grade B” indicates that there is a small amount of fuzziness on a slit separator. “Grade C” indicates that there is a large amount of fuzziness on a slit separator (there are more than one occurrences of visible fuzziness).
These are examples in each of which (i) a plate knife (manufactured by Kyocera Corporation, FBC4019G, blade edge cross-sectional angle: 25°) was attached to a slitting apparatus (manufactured by Hagihara Industries Inc., model: HDF-105S-1000) and then (ii) in accordance with the conditions shown in Table 1, the laminated porous film A was slit while being moved along a roll having a diameter of 80 mm.
These are examples in each of which (i) gable blades (manufactured by Kyocera Corporation, upper blade: GUBD-09807T45DC15 (blade edge cross-sectional angle: 45°) and a lower blade: GDBD-08005T) were attached to a slitting apparatus (manufactured by Hagihara Industries Inc., model: HDF-924-1900) and then (ii) in accordance with the conditions shown in Table 1, the laminated porous film B was slit while being moved along the lower blade.
These are examples in each of which (i) gable blades (manufactured by Kyocera Corporation, upper blade: GUBD-09807T60DC15 (blade edge cross-sectional angle: 60°), lower blade: GDBD-08005T) were attached to a slitting apparatus (manufactured by Hagihara Industries Inc., model: HDP-924-1900) and then (ii) in accordance with the conditions shown in Table 1, the laminated porous film A was slit while being moved along the lower blade.
(Other Slitting Conditions)
Note that an upper blade of gable blades is a single-beveled blade. Therefore, in Examples 2 to 6 and Comparative Example 2 in each of which such gable blades are used, the tangent-plane blade edge angle θ3 is θ3a which is a value obtained by substituting the cross-sectional angle θ1 into θ1a of the above Formula (12).
Note also that a conveyance speed of a separator at a part at which the separator is slit is not less than 50 m/min and not more than 100 m/min. Note also that a take-up tensile force of the separator is not less than 30 N/m and not more than 90 N/m.
<<Verification Results of Separator Slitting Method>>
The tangent-plane blade edge angle θ3 is preferably not less than 3° and not more than 35°, more preferably not less than 3° and not more than 21°, and even more preferably not less than 5° and not more than 21°.
Specifically, the fuzziness amounts in Examples 1through 6 are each at the grade A or B. Meanwhile, the fuzziness amounts in Comparative Examples 1 and 2 are each at the grade C. This means that in a case where the tangent-plane blade edge angle θ3 is in a range of not less than 3° to not more than 35°, it is possible to obtain a good-quality slit separator having a small amount of fuzziness at a slit part thereof
In particular, the fuzziness amounts in Examples 1 to 4 are each at the grade A. This means that in a case where the tangent-plane blade edge angle θ3 is in a range of not less than 5° to not more than 21°, it is possible to obtain a good-quality slit separator having a smaller amount of fuzziness at a slit part thereof.
The quality of a slit separator thus depends on a tangent-plane blade edge angle θ3. In other words, it can be said that as long as the tangent-plane blade edge angle θ3 remains at the identical value, it is possible to obtain a slit separator of the identical quality even if any of the following changes: a type of a separator to be slit; a type of a slitting blade (flat blade, circular blade); a cross-sectional shape (double-beveled blade, single-beveled blade) of a slitting blade, a cross-sectional angle θ1 of a blade edge of the slitting blade; and a mounting angle θ2 of the slitting blade.
The following description will discuss Embodiment 4 of the present invention.
<<Configurations for Maintaining Consistent Tangent-Plane Blade Edge Angles Among a Plurality of Slitting Blades>>
As illustrated in (a) of
Note that as slitting continues, slitting blades 72c are each increasingly abraded. In addition, a defect M such as chipping occurs to a slitting blade (s) 72c in some cases. As illustrated in (b) of
As illustrated in (d) of
As illustrated in (f) of
(Change in Tangent-Plane Blade Edge Angle)
As illustrated by two-dot chain lines in (a) of
In this case, by calculating the tangent-plane blade edge angle θ3 by substituting the cross-sectional angle θ1 of a blade edge E of the slitting blade 72 and the mounting angle θ2 after the change into the Formula (6), it is possible to calculate the tangent-plane blade edge angles θ3A and θ3B.
Furthermore, as illustrated in (a) of
Respective tangent-plane blade edge angles of the slitting blade 72a which is a circular blade, the slitting blade 72b which is a single-beveled slitting blade, and the pair of slitting blades 72c and 72d are changed similarly with the tangent-plane blade edge angle θ3 of the slitting blade 72. Various types of the slitting blades above will be hereinafter referred to merely as “slitting blade”.
(Method for Producing Slit Separator Whose Change in Tangent-Plane Blade Edge Angle is Prevented)
As illustrated in (c) of
In this configuration, in the step S102a, the tangent-plane blade edge angles θ3 of a plurality of slitting blades are within the range of the angle θc±Δ.
The plurality of slitting blades indicate, for example, a plurality of slitting blades 72 illustrated in (b) of
The angle θc is a target value of the tangent-plane blade edge angles θ3 of the plurality of slitting blades as above, and is within, for example, the above range α.
Δ is a positive number and is a value indicating a range within which the tangent-plane blade edge angle θ3 is changed from the angle θc. In a case where Δ is so small that the angle (θc−Δ) and the angle (θc+Δ) are each within a predetermined range (e.g. the aforementioned range α), tangent plane blade edge angles θ3 of a plurality of slitting blades can be treated as being a substantially identical angle θc.
In the step S102a, tangent-plane blade edge angles θ3 of a plurality of slitting blades may be within a range of not less than the angle (θc−ΔA) and not more than the angle (θc+ΔB). In this case, ΔA and ΔB are 0 of a positive number and are different from each other. In a case where ΔA and ΔB are so small that the angle (θc−ΔA) and the angle (θc+ΔB) are each within a predetermined range (e.g. aforementioned range α), tangent-plane blade edge angles θ3 of a plurality of slitting blades can be treated as being a substantially identical angle θc.
(Target Value and Variable Range of Tangent-Plane Blade Edge Angle)
As described above, tangent-plane blade edge angles θ3 of a plurality of slitting blades being substantially identical with each other is equal to presence of the angle θc and Δ which allow the angle (θc−Δ) and the angle (θc+Δ) to be each within a predetermined range.
The predetermined range herein is such a range that when the tangent-plane blade edge angles θ3 are within that range, a good-quality slit separator having a small amount of fuzziness at a slit part thereof can be obtained. For example, the range of not less than 11.9° and not more than 20.1° which is a range of the tangent-plane blade edge angle θ3 shown in Examples 2-4 of Table 1 can be considered as the predetermined range.
For example, the angle θc is set to 16.0° which is an average of 11.9° and 20.1°. Furthermore, Δ is set to 4.1° which is a difference between 20.1° and 16.0°. In this case, the angle (θc−Δ) is 11.9°. The angle (θc+Δ) is 20.1°. Accordingly, the angle θc and Δ which allow the angle (θc−Δ) and the angle (θc+Δ) to be each within a predetermined range are present.
(Step of Slitting Original Sheet with Use of a Plurality of Slitting Blades)
The step S102a which is a step of slitting the original sheet S with use of a plurality of slitting blades is specifically a step of slitting the original sheet S by causing the plurality of slitting blades to cut into the original sheet S such that the tangent-plane blade edge angles θ3 are substantially identical with each other.
In other words, the step S102a is a step of slitting the original sheet S by causing a plurality of slitting blades to cut into the original sheet S such that the tangent-plane blade edge angles θ3 are each within a predetermined range.
The predetermined range may be such a range that, for example, when the tangent-plane blade edge angles θ3 are within that range, a good-quality slit separator having a small amount of fuzziness at a slit part thereof can be obtained.
Causing a plurality of slitting blades to cut into the original sheet S such that the tangent-plane blade edge angles θ3 are each within a predetermined range indicates causing a plurality of slitting blades, each of which has a cross sectional angle θ1 within a range that meets the relation of the aforementioned Formula (5) (e.g. not less than 45° and not more than 60°) and has a mounting angle θ2 within a range that meets the relation of the Formula (5) (e.g. not less than 12.2° and not more than 17.3°) to cut into the original sheet S, with the tangent-plane blade edge angles θ3 each being within a predetermined range (e.g. not less than 11.9° and not more than 20.1°).
(Method for Producing Slit Separator, Which Maintains Consistent Abrasion State of Slitting Blade)
As illustrated in (d) of
In the step S102a, as illustrated in (d) of
In the step S102b, the original sheet conveyed in the step S101a is slit with use of slitting blades identical with those having slit the original sheet S in the step S102a. That is, in order that a plurality of slitting blades have constant degree of abrasion or constant frequency of defects, the number of slitting blades used is an appropriate number corresponding to the width of the original sheet S to be slit in the step S102a and the width of the other original sheet to be slit in the step S102b.
In this case, the tangent-plane blade edge angles θ3 of the slitting blades used for slitting are each within a range of the angle θc±Δ.
<<Effects of the Present Embodiment>>
As illustrated in
In the method for producing a slit separator illustrated in (c) of
In this case, the tangent-plane blade edge angles θ3 affect fuzziness that occurs at the slit part of the slit separator. The fuzziness can be effectively suppressed by causing the tangent-plane blade edge angles θ3 to be substantially identical with each other (θc−Δ≦θ3≦θc+Δ).
With the method for producing a slit separator, it is possible to obtain, all at once, a plurality of good-quality slit separators with a small amount of fuzziness at slit parts thereof.
The Δ is preferably not more than 5°, more preferably not more than 3°, and further more preferably not more than 1°.
In this case, since slit parts of the plurality of slit separators have substantially identical fuzziness, quality of the plurality of slit separators is stable. As Δ is smaller, the slit parts of the plurality of slit separators have further identical fuzziness, so that the quality of the plurality of slit separators is more stable.
With the method for producing a slit separator as illustrated in (d) of
As illustrated in (b) of
A method for producing a slit separator in accordance with Aspect 1 of the present invention includes: a conveying step of conveying a battery separator original sheet which is porous; and a first slitting step of slitting the battery separator original sheet by causing a plurality of slitting blades to cut into the battery separator original sheet such that a plurality of slitting blade edge angles in a tangent plane, on which a slitting position is in contact with the battery separator original sheet, are substantially identical with each other.
In a case where a battery separator original sheet which is porous is slit, fuzziness can easily occur at a slit part(s) because of porousness of the battery separator original sheet.
In this case, a slitting blade edge angle (hereinafter, referred to as “tangent-plane blade edge angle”) in a tangent plane, on which a slitting position is in contact with a battery separator original sheet, affects fuzziness that occurs at the slit part of the separator. By causing the tangent-plane edge angles to be substantially identical with each other, it is possible to effectively prevent fuzziness.
With the method, it is possible to obtain, all at once, a plurality of good-quality slit separators with a small amount of fuzziness at a slit part thereof.
It is preferable to arrange the method such that in the first slitting step, a film obtained by slitting the battery separator original sheet is obtained by slitting with use of adjacent two slitting blades out of the plurality of slitting blades.
With the method, it is possible to obtain a better-quality slit separator with a small amount of fuzziness at a slitting part, thereof at both ends of the slit, film in a width direction.
It is preferable to arrange the method such that the plurality of slitting blades are attached to a single axis positioned fixedly with respect to the battery separator original sheet.
With the method, the plurality of slitting blades are positioned fixedly with respect to the battery separator original sheet via the single axis. Consequently, it is possible to surely cause the plurality of slitting blades to cut into the battery separator original sheet such that tangent-plane blade edge angles of the plurality of slitting blades are substantially identical with each other.
It is preferable to arrange the method such that at least one of the plurality of slitting blades is a flat blade and is rotatably attached to the axis.
With the method, it is possible to cause the flat blade rotatably attached to the axis to rotate and adjust the angle of the flat blade. This allows fine adjustment such that tangent-plane blade edge angles of slitting blades are substantially identical with each other.
It is preferable to arrange the method such that a rotational angle of said at least one slitting blade rotatably attached to the axis is limited by a stopper positioned fixedly with respect to the axis.
With the method, it is possible to stop the slitting blade rotatably attached to the axis and limit the angle of the slitting blade. This surely allows adjustment such that tangent-plane blade edge angles of the slitting blades are substantially identical with each other.
It is preferable to arrange the method such that in the first slitting step, two or more slitting blades being a part of the plurality of slitting blades slit the battery separator original sheet, and the method further comprises: a second conveying step of conveying other battery separator original sheet which is porous and has a same width as that of the battery separator original sheet; and a second slitting step of slitting the battery separator original sheet by causing said two or more slitting blades to cut into the other battery separator original sheet such that slitting blade edge angles of said two or more slitting blades in a tangent plane, on which a slitting position is in contact with the other battery separator original sheet, are substantially identical with each other.
With the method, it is possible to use the same slitting blades both for a plurality of slitting blades to slit the battery separator original sheet in the first slitting step and for a plurality of slitting blades to slit other battery separator original sheet in the second slitting step. This allows the slitting blades to be consistent with each other in terms of the extent of abrasion or the frequency of defect occurrences.
It is preferable to arrange the method so as to further include the step of replacing the plurality of slitting blades all at once.
With the method, ii is possible to replace, all at once, slitting blades which are abraded to the same extent or to which defect is likely to occur to the same extent.
The method may be arranged such that the battery separator original sheet contains inorganic filler.
In a case where a battery separator original sheet containing inorganic filler is slit, slitting blades are abraded with a faster pace. However, with the method, even in the case where such a battery separator original sheet is slit, it is possible to obtain, all at once, a plurality of good-quality slit separators with a small amount of fuzziness at slit parts thereof.
Furthermore, by fixing a slitting blade with use of the aforementioned stopper, it is possible to prevent erroneously change the position or angle of the slitting blade with respect to the battery separator original sheet. This method is useful particularly in the case where the battery separator original sheet containing inorganic filler is slit because in such a case a slitting blade is abraded with a faster pace.
It is preferable to arrange the method such that in the first slitting step, the battery separator original sheet is slit by causing the plurality of slitting blades to cut into the battery separator original sheet such that the plurality of slitting blade edge angles are each within a predetermined range.
It is preferable to arrange the method such that in the first slitting step, the battery separator original sheet is slit fay causing the plurality of slitting blades, each of which has a cross sectional angle θ1 within a range that meets Formula (5) below and has a mounting angle θ2 within a range that meets Formula (5) below, to cut into the battery separator original sheet, with the plurality of slitting blade edge angles being θ3 within a predetermined range.
tan(θ3/2)=sin(θ2)·tan(σ1/2) Formula (5)
It is preferable to arrange the method such that the predetermined range of the plurality of slitting blade edge angles is a range that enables the method to produce a good-quality slit separator with a small amount of fuzziness at a slit part thereof.
A method for producing a separator roll in accordance with Aspect 2 of the present invention includes: each of the steps recited in the aforementioned method for producing a slit separator; and a winding step of winding, around a core, a separator obtained by slitting the battery separator original sheet.
When a slit separator obtained by slitting a battery separator original sheet is wound around a core, fuzz occurring on side parts of the slit separator in a width direction appears on an end surface of the side parts of a separator roll.
With the method, it is possible to obtain, all at once, a plurality of good-quality separator rolls with a small amount of fuzziness on an end surface of the side parts of each of the separator rolls.
A method for producing a slit separator in accordance with Referential Aspect 1 of the present invention includes: a conveying step of conveying a battery separator original sheet which is porous; and a slitting step of slitting the battery separator original sheet by causing a slitting blade to cut into the battery separator original sheet such that a slitting blade edge angle in a tangent plane, on which a slitting position is in contact with the battery separator original sheet, is in a range of not less than 3° to not more than 35°.
The battery separator original sheet which is porous has a tendency that, due to its porosity, a slit part thereof is likely to have fuzziness when the battery separator original sheet is slit.
The inventors found that (i) a slitting blade edge angle (hereinafter, referred to as “tangent-plane blade edge angle”) in a tangent plane, on which a slitting position is in contact with a battery separator original sheet, affects fuzziness that occurs at the slit part of the separator and (ii) the fuzziness can be effectively suppressed by causing the tangent-plane blade edge angle to be in a range of not less than 3° to not more than 35°.
With the method, it is possible to obtain a good-quality slit separator having a small amount of fuzziness at a slit part thereof.
The slit separator production method is preferably configured such that the slitting blade edge angle is not more than 28°.
With the method, it is possible to obtain a good-quality slit separator having a smaller amount of fuzziness at a slit part thereof.
It is more preferable to arrange the method such that the slitting blade edge angle is a range of not less than 5° to not more than 21°.
With the method, it is possible to obtain a superior-quality slit separator having an even smaller amount of fuzziness at a slit part thereof.
The method may be arranged such that the battery separator original sheet has, at the slitting position, a curved surface that is convexed toward the slitting blade.
With the method, the tangent-plane blade edge angle is determined by a length at which the blade edge of the slitting blade is inserted into the curved surface. This allows the tangent-plane blade edge angle to be easily adjusted.
The method may be arranged such that a blade edge of the slitting blade is arc-shaped.
With the method, the tangent-plane blade edge angle Is determined by a length at which the blade edge of the slitting blade is inserted into the battery separator original sheet being conveyed. This allows the tangent-plane blade edge angle to be easily adjusted.
The method may be arranged such that a shape of the blade edge of the slitting blade is plane-symmetrical with respect to a plane, the plane being (i) perpendicular to the tangent plane and (ii) parallel to a direction in which the battery separator original sheet is conveyed.
With the method, it is possible to obtain slit separators whose respective end surfaces, at which the slit separators have been slit, are closer to being uniform.
A separator roll production method in accordance with Referential Aspect 2 of the present invention includes: each of the steps recited in the slit separator production method; and a winding step of winding, around a core, a separator which has been slit.
With the method, a separator roll, which is made up of a core and a separator wound around the core, is obtained. In this case, a slit part of the separator corresponds to a surface of the roll, which surface is located on a side-surface side of the core. By use of the above-described slit separator production method, it is possible to obtain a good-quality slit separator having a small amount of fuzziness at a slit part thereof. This makes it possible to obtain a good-quality separator roll having a surface on which there is a small amount of fuzziness.
A separator slitting method in accordance with Referential Aspect 3 of the present invention includes: a conveying step of conveying a battery separator original sheet which is porous; and a slitting step of slitting the battery separator original sheet by causing a slitting blade to cut into the battery separator original sheet such that a slitting blade edge angle in a tangent plane, on which a slitting position is in contact with the battery separator original sheet, is in a range of not less than 3° to not more than 35°.
A separator slitting apparatus in accordance with Referential Aspect 4 of the present invention includes: a conveying section for conveying a battery separator original sheet which is porous; and a slitting blade for slitting the battery separator original sheet, a blade edge angle in a tangent plane, on which a slitting position of the slitting blade is in contact with the battery separator original sheet, being in a range of not less than 3° to not more than 35°.
[Additional Remarks]
The present invention is not limited to the embodiments, but can be altered by a skilled person in the art within the scope of the claims. An embodiment derived from a proper combination of technical means each disclosed in a different embodiment is also encompassed in the technical scope of the present invention.
The present invention can be used for (i) a method for slitting a film in any direction, (ii) a method for producing a film roll, and (iii) a film slitting apparatus.
1 Lithium-ion secondary battery
3 Lithium ion
4 Heat resistant layer
6 Slitting apparatus (separator slitting apparatus)
7 Cutting device
12 Separator
66 Roller (conveying section)
71 Holder
72,72a through 72d Slitting blade
E,Ea,Ec Blade edge
P Pore
S Original sheet (separator)
S101 Step of conveying separator original sheet, first conveying step
S101a Step of conveying other separator original sheet, second conveying step
S102 Step of slitting separator original sheet
S102a Step of slitting separator original sheet, first slitting step
S102b Step of slitting separator original sheet, second slitting step
T Cross section (tangent plane)
θ1,θ1a,θ4 Cross-sectional angle
θ2 Mounting angle
θ2a,θ2b Entry angle
θ2cc,θ2cd One entry angle
θ3,θ3a Tangent-plane blade edge angle
Number | Date | Country | Kind |
---|---|---|---|
2014-263594 | Dec 2014 | JP | national |
PCT/JP2015/065010 | May 2015 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2015/085842 | 12/22/2015 | WO | 00 |