Patent Application
20180002136
This Nonprovisional application claims priority under 35 U.S.C. §119 on Patent Application No. 2016-250240 filed in Japan on Dec. 23, 2016, and on Patent Application No. 2016-130288 filed in Japan on Jun. 30, 2016, the entire contents of both of which are hereby incorporated by reference.
The present invention relates to (i) a method for cleaning a separator core which is used in winding a separator for a nonaqueous electrolyte secondary battery (hereinafter referred to as a “nonaqueous electrolyte secondary battery separator”), (ii) a separator roll, and (iii) a method for producing the separator roll.
Patent Literature 1 discloses an example of a separator core around which a separator is wound when being provided as a product, the separator having been produced continuously while being transferred via a transfer system such as a roller. The separator produced thusly is provided as a separator roll wound around an outer peripheral surface of the separator core.
[Patent Literature 1]
Japanese Patent Application Publication Tokukai No. 2013-139340 (Publication date: Jul. 18, 2013)
In a separator core which has been used and from which a separator has been wound off, there are cases in which a foreign object, such as an electrically conductive foreign object, is adhered to the separator core. If the separator core having such a foreign object adhered thereto is reused as is, the foreign object can adhere to a separator to be wound around the separator core. This can cause a product defect such as a short circuit in a nonaqueous electrolyte secondary battery produced using the separator.
An embodiment of the present invention has been made in view of the above problem. An object of an embodiment of the present invention lies in preventing adherence of a foreign object to a separator, which adherence occurs in reuse of a separator core.
In order to solve the above problem, a method for cleaning a separator core in accordance with an embodiment of the present invention is a method for cleaning a separator core having an outer peripheral surface around which a nonaqueous electrolyte secondary battery separator is to be wound, the method including: an end face cleaning step of removing a foreign object adhered to an end face of the separator core.
An embodiment of the present invention brings about the effect of providing (i) a method for cleaning a separator core, (ii) a separator roll, and (iii) a method for producing the separator roll, each of which makes it possible to prevent adherence of a foreign object to a separator, which adherence occurs in reuse of a separator core.
(a) of
The following description will discuss an embodiment of the present invention with reference to
Note that in the present specification, “cleaning” refers to an operation performed to remove foreign objects from a separator core. In other words, the term “cleaning” as used in the present specification is not limited to an operation to remove foreign objects from a separator core by use of a cleaning liquid, but rather includes any of various types of operations for removing foreign objects from a separator core, such as (i) removing foreign objects from a separator core by scouring off the foreign objects and (ii) removing foreign objects from a separator core by wiping the separator core.
Discussed first is a lithium-ion secondary battery (nonaqueous electrolyte secondary battery) including a nonaqueous electrolyte secondary battery separator (hereinafter also referred to as a “separator”) which had been wound around the separator core in accordance with Embodiment 1.
<Configuration of Lithium-Ion Secondary Battery>
The following description will discuss a configuration of a lithium-ion secondary battery with reference to
<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 separates the cathode 11 and the anode 13, allowing lithium ions to move between the cathode 11 and the anode 13. For example, polyolefin such as polyethylene or polypropylene is used as a material of the separator 12.
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 2, 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
In the configuration illustrated in (a) of
As illustrated in (b) of
<Steps of Producing Separator and Heat-Resistant Separator>
How to produce the separator 12 and the heat-resistant separator 12a of the lithium-ion secondary battery 1 is not particularly limited. The separator 12 and the heat-resistant separator 12a can be produced by a publicly known method. The following discussion assumes a case where a porous film serving as a raw material of the separator 12 (heat-resistant separator 12a) contains polyethylene as a main material. Note, however, that even in a case where the porous film contains another material, the separator 12 (heat-resistant separator 12a) can be produced by employing a similar production method.
Examples of such a similar production method encompass a method which includes the steps of forming a film by adding inorganic filler or a plasticizer to a thermoplastic resin, and then removing the inorganic filler or the plasticizer by means of an appropriate solvent. For example, in a case where the porous film is a polyolefin separator made of a polyethylene resin containing ultra-high molecular weight polyethylene, it is possible to produce the porous film by the following method.
This method includes (1) a kneading step of obtaining a polyethylene resin composition by kneading a ultra-high molecular weight polyethylene with (i) an inorganic filler (such as calcium carbonate or silica) or (ii) a plasticizer (such as low molecular weight polyolefin or fluid paraffin), (2) a rolling step of forming a film by means of the polyethylene resin composition, (3) a removal step of removing the inorganic filler or the plasticizer from the film obtained in the step (2), and (4) a stretching step of obtaining the porous film by stretching the film obtained in the step (3). The step (4) can be alternatively carried out between the steps (2) and (3).
In the removal step, many fine pores are formed in the film. The fine pores of the film stretched in the stretching step serve as the above-described pores P. The porous film (separator 12) is thus obtained. Note that the porous film is a polyethylene microporous film having a prescribed thickness and a prescribed air permeability.
Note that, in the kneading step, (i) 100 parts by weight of the ultra-high molecular weight polyethylene, (ii) 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 (iii) 100 parts by weight to 400 parts by weight of the inorganic filler can be kneaded.
The heat-resistant separator 12a can be produced by disposing the heat-resistant layer 4, as a functional layer, on a surface of the separator 12 obtained as above. The functional layer is disposed on the separator 12 by (i) coating the separator 12 with a coating material (a material) corresponding to the functional layer and then (ii) drying the separator 12. Note that production of the heat-resistant separator 12a is discussed in detail in Embodiment 2, in a section discussing a method for producing a separator roll.
The separator 12, which does not include the heat-resistant layer 4, and the heat-resistant separator 12a (hereinafter also referred to as “separator”) each preferably has a width (hereinafter referred to as “product width”) suitable for application products such as the lithium-ion secondary battery 1. For improved productivity, however, a separator is produced so as to have a width that is equal to or greater 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 cut (slit) so as to have the product width and wound around a core (separator core).
Note that the expression “width of a/the separator” means a dimension of the separator in a direction that is parallel to a plane in which the separator extends and that is perpendicular to the longitudinal direction of the separator. Hereinafter, a wide separator which has not been subjected to slitting is also referred to as an “original sheet.” Note also that (i) “slitting” means to slit the separator in the longitudinal direction (flow direction of the separator during production; MD: Machine direction) and (ii) “cutting” means to slit the separator in a transverse direction (TD). Furthermore, “transverse direction (TD)” means a direction that is parallel to a plane in which the separator extends and that is substantially perpendicular to the longitudinal direction (MD) of the separator.
<Structure of Core>
The following description will discuss a configuration of the core 5 with reference to
As illustrated in (a) of
The respective central axes of the outer cylindrical member 51 and the inner cylindrical member 52 preferably substantially match each other but are not limited to such a configuration. Furthermore, dimensions of the outer cylindrical member 51 and the inner cylindrical member 52, such as the respective thicknesses, widths, and radii thereof, can be designed as necessary in accordance with, for example, the type of separator to be wound.
With regards to a material of the core 5, a resin containing any of ABS resin, polyethylene resin, polypropylene resin, polystyrene resin, polyester resin, and a vinyl chloride resin can be suitably used. This makes it possible to produce the core 5 by resin molding which uses a metal mold.
As illustrated in (b) of
<Problems when Reusing Core>
Once the core 5 has been used and the separator wound off from the separator roll 6, there are cases in which a foreign object, such as an electrically conductive foreign object, is adhered to the core 5. Such a foreign object is particularly likely to adhere to end faces 55 of the core 5 (that is, to side faces of the core 5 which face away from each other in the axial direction). In a case where the core 5 has such a foreign object adhered thereto and is reused as is, the foreign object can adhere to a separator wound around the core 5. This can cause a product defect such as a short circuit in a lithium-ion secondary battery 1 produced using the separator.
Furthermore, since a cutter or the like may be used when cutting the separator off from the core 5, there is the risk that the outer peripheral surface 54 of the core 5 will be damaged. In a case where the core 5 having such damage is reused as is, unevenness caused by the damage can cause damage to a new separator wound around the core 5. This can cause a product defect such as a short circuit in a lithium-ion secondary battery 1 produced using the separator.
In this way, if the core 5, after having been used, is reused as is, there is the risk that a foreign object will adhere to a separator and the risk that the separator will be damaged. In Embodiment 1, such adherence of a foreign object to the separator and damage to the separator is prevented by cleaning the core 5 after it has been used.
<Method for Cleaning Core>
(Exterior Inspection Step)
The exterior inspection step S1 is a step of inspecting the core 5 that has been used, in order to determine whether or not the core 5 has a defect. In the exterior inspection step S1, the core 5, having been used, is screened by using a boundary sample as a standard and visually confirming whether or not the core 5 has a defect such as cracking or chipping. In a case where no defect such as cracking or chipping is found in the core 5 in the exterior inspection step S1, the core 5 is sent to the next step.
<Label Removal Step>
The label removal step S2 is step of removing a label (for example, a label indicating product information relating to a separator) which has been affixed to the core 5.
(Outer Peripheral Surface Cleaning Step)
The outer peripheral surface cleaning step S3 is a step of cleaning the outer peripheral surface 54 of the core 5. After the core 5 is used, a foreign object, such as an aramid resin contained in the heat-resistant layer 4, may be adhered to the outer peripheral surface 54. It is preferable that such a foreign object adhered to the outer peripheral surface 54 of the core 5 be removed via the outer peripheral surface cleaning step S3.
(End Face Cleaning Step)
The end face cleaning step S4 is a step of cleaning an end face 55 of the core 5. After the core 5 is used, a foreign object is particularly likely to be adhered to the end faces 55 of the core. Examples of such a foreign object include a cathode material (such as a lithium-based alloy) and an anode material (such as a graphite-based carbon material), each of which is used in production of a nonaqueous electrolyte secondary battery (lithium-ion secondary battery 1). It is preferable that such a foreign object adhered to an end face 55 of the core 5 be removed via the end face cleaning step S4.
It is preferable that a sheet having suitable elasticity and suitable frictional resistance is used as the pressure-contact sheet 72. For example, a resin foam sheet such as a vinyl chloride foam sheet can be suitably used as the pressure-contact sheet 72. It is preferable that the surface of the pressure-contact sheet 72 has asperities or a plurality of micropores. This makes it possible to improve the wiping effect of the pressure-contact sheet 72.
Furthermore, in the end face cleaning step S4, the pressure-contact sheet 72 can be used to wipe away a foreign object adhered to an end face 55 of the core 5 after carrying out a treatment, such as immersing the end face 55 of the core 5 into a solvent. This makes it possible to improve the effect of cleaning the end face 55 of the core 5.
An aprotic solvent is preferably used as the solvent. In a case where the core 5 is configured to include a material such as ABS resin, using alcohol as the solvent is likely to cause the core 5 deteriorate. An aprotic solvent can be used as the solvent to increase the effect of cleaning the end face 55 of the core 5 while also preventing deterioration of the core 5. A nonpolar solvent is preferably used as the aprotic solvent. For example, a hydrocarbon (such as decane) can be suitably used. In addition to being unlikely to cause deterioration of the core 5, such a nonpolar solvent is also preferable due to being volatile. This is because such volatility makes it unnecessary to carry out a step of drying the core 5 after cleaning.
A liquid obtained by adding a surfactant to water can also be used as the solvent. The liquid is preferably heated to a temperature of 40° C. to 90° C. prior to use, as doing so increases the effect of cleaning. The liquid is more preferably heated to a temperature of 50° C. to 70° C.
In the end face cleaning step S4, as an alternative to the method of using a pressure-contact member in the form of a sheet (that is, the pressure-contact sheet 72) to wipe away a foreign object adhered to the end face 55 of the core 5, it is possible to employ a method of washing away the foreign object adhered to the end face 55 of the core 5 by causing a liquid which has been accelerated to impact the end face 55 of the core 5. Examples of a liquid to be used include the above aprotic solvent and the liquid obtained by adding a surfactant to water. The liquid obtained by adding a surfactant to water is preferably used.
(Unevenness Inspection Step)
The unevenness inspection step S5 is a step of inspecting the core 5 in order to determine whether or not there is damage to the outer peripheral surface 54 of the core 5. As discussed above, since a cutter or the like is used when cutting the separator off from the core 5, there is the risk that there will be damage present in the outer peripheral surface 54 of the core 5 after the core has been used. In the unevenness inspection step S5, it is confirmed whether or not there is damage to the outer peripheral surface 54 of the core 5. In a case where there is damage, the damage is repaired in the damage repair step S6 which follows. This makes it possible to avoid reusing the core 5 in a state where there remains damage to the outer peripheral surface 54 thereof.
(Damage Repair Step)
The damage repair step S6 is a step of repairing damage to the outer peripheral surface 54 of the core 5. In a case where damage to the outer peripheral surface 54 is found in the unevenness inspection step S5, unevenness of the outer peripheral surface 54 caused by such damage is reduced in the damage repair step S6. This is done by smoothing the damage by use of a scraper or the like. The damage repair step S6 can be omitted in a case where no damage to the outer peripheral surface 54 of the core 5 is found in the unevenness inspection step S5.
(Whole Core Cleaning Step)
The whole core cleaning step S7 is a step of wiping the whole of the core 5 with, for example, a fabric (fiber member) moistened with a solvent. The outer cylindrical member 51, the inner cylindrical member 52, and the plurality of ribs 53 constituting the core 5 are wiped in the whole core cleaning step S7. This makes it possible to more reliably remove, from all surfaces of the core 5, any foreign object adhered thereto.
(Foreign Object Inspection Step)
The foreign object inspection step Sa is a step of inspecting the core 5 which has been cleaned in the end face cleaning step S4, in order to determine whether a foreign object is adhered to the core 5. The foreign object inspection step Sa is carried out under lighting which has a color temperature in a range from 2500 K to 7000 K and a special color rendering index R15 of not less than 60. The lighting is typically a light emitting diode (LED) but can alternatively be a fluorescent lamp, a light bulb, or the like.
Japan Industrial Standards (JIS) Z 8726:1990 (“Method of specifying color rendering properties of light sources”) prescribes the use of general color rendering indices R1 through R8 and special color rendering indices R9 through R15 as indices for specifying color rendering properties of light sources. Of these indices, the special color rendering index R15 can be described as “Japanese skin color” and is defined as having, in the Munsell color system, a hue of 1YR, a value of 6, and a chroma of 4.
With the foreign object inspection step Sa, any black electrically conductive material or white material that has adhered to the core 5 is adequately visible. As such, in a case where black electrically conductive material or white material has adhered to the core 5 as a foreign object, the foreign object inspection step Sa makes it easy to quickly find such a foreign object. With the foreign object inspection step Sa, therefore, it is possible to shorten the amount of time of an inspection step required for reuse of the core 5.
Table 1 indicates a relationship between (i) the type of lighting used in an inspection step to determine whether a foreign object is adhered to the core 5, after the core 5 has been cleaned in the end face cleaning step S4, and (ii) the ease with which dirt (a foreign object), adhered to the core 5, can be found.
In creating Table 1, tests were performed using, as the core 5, (i) a white core (5Y 9.0/2.0) having, in the Munsell color system, a hue of 5Y, a value of 9.0, and a chroma of 2.0 and (ii) a red core (5R 4.0/12.0) having, in the Munsell color system, a hue of 5R, a value of 4.0, and a chroma of 12.0. Dirt was caused to adhere to the cores 5 indicated in Table 1 in the following manner. First, a lead (length: 10 mm; thickness: 2 mm) was removed from an HB pencil (manufactured by Mitsubishi Pencil Co., Ltd.; “Office-use pencil 9800”). The lead was set in a fastness friction testing apparatus (manufactured by Toyo Seiki Seisaku-sho, Ltd.; model D) so as to produce a mark which would measure 10 mm wide after friction testing. The lead set thusly was then rubbed onto a test piece (width: 15 mm; length 45 mm; thickness: 6 mm; made from ABS) of the core 5. Specifically, the lead was rubbed back and forth 10 times along a center portion of the test piece in a longitudinal direction using a load of 200 g. Next, the lead was replaced with a paper wipe (manufactured by Nippon Paper Crecia Co., Ltd.; “Kimwipe S-200”; 120 mm×215 mm) which had been folded in half. The paper wipe was caused to soak up ethanol (1 mL) and then rubbed back and forth once on the test piece of the core 5 using a load of 200 g. What remained of the mark from the lead was considered to be the “dirt” on the core 5.
An inspection was then carried out to determine whether or not dirt, produced under the above conditions, was adhered to the core 5. The inspection was carried out under various lighting defined by the combinations of color temperature, special color rendering index R15, and illuminance indicated in Table 1. The differences in combinations are indicated in Table 1 as Examples 1 through 4 and Comparative Examples 1 and 2. The visual noticeability of the dirt was then determined using the following criteria.
Presence of dirt is clearly noticeable: A
Presence of dirt is noticeable with careful inspection: B
Presence of dirt is difficult to determine: C
Presence of dirt is nearly impossible to determine: D
From Examples 1 through 4 in Table 1, it was found that in order to determine the presence of dirt adhered to the core 5, color temperature is preferably in a range from 2500 K to 7000 K. It was further found, from Examples 1 through 4 and Comparative Example 1 in Table 1, that in order to determine the presence of dirt adhered to the core 5, the special color rendering index R15 is preferably not less than 60. It was also found, from Examples 1 through 4 in Table 1, that in order to determine the presence of dirt adhered to the core 5, the special color rendering index R15 is preferably not more than 95, and more preferably not more than 90.
Note that, although in
Furthermore, in the foreign object inspection step Sa, the presence or absence of a foreign object adhered to the core 5 can be determined by a visual inspection or can alternatively be determined by an inspection using a machine, such as an optical inspection apparatus or the like.
Furthermore, an inspection to determine whether or not a foreign object is adhered to the core 5, which inspection is carried out under lighting having a color temperature in a range from 2500 K to 7000 K and a special color rendering index R15 of not less than 60 (preferably of not more than 95 and more preferably of not more than 90) is not limited to use in the foreign object inspection step Sa. That is, in a case where black electrically conductive material or white material is adhered to the core 5 as a foreign object, the above inspection makes it easy to quickly find such a foreign object, regardless of whether the inspection is carried out in the foreign object inspection step Sa. In other words, Embodiment 1 includes in its scope a method for inspecting the core 5, which method includes a step of inspecting the core 5, in order to determine whether a foreign object is adhered thereto, the inspecting being carried out under lighting having a color temperature in a range from 2500 K to 7000 K and a special color rendering index R15 of not less than 60.
As described above, a method for cleaning the core 5 in accordance with Embodiment 1 includes (i) the end face cleaning step S4 of removing a foreign object adhered to an end face 55 of the core 5 and (ii) the unevenness inspection step S5 of inspecting the core 5 in order to determine whether or not there is damage to the outer peripheral surface 54 of the core 5
In a method for cleaning the core 5 in accordance with Embodiment 1, a foreign object adhered to an end face 55 of the core 5 is removed in the end face cleaning step S4. This makes it possible to prevent a foreign object from adhering to a separator wound around the core 5 when the core 5 is reused.
Furthermore, in a method for cleaning the core 5 in accordance with Embodiment 1, the core 5 is inspected, in the unevenness inspection step S5, in order to determine whether or not there is damage to the outer peripheral surface 54 of the core 5. This makes it possible to avoid reusing the core in a state where there remains damage to the outer peripheral surface 54 thereof. This, in turn, makes it possible to prevent a separator which is to be wound around the core 5 from being damaged by unevenness due to such damage to the core 5.
As such, Embodiment 1 makes it possible to realize a method for cleaning the core 5 which can suitably prevent, in reuse of the core 5, (i) adherence of a foreign object to a separator and (ii) damage to the separator.
The following description will discuss another embodiment of the present invention with reference to
<Method for Producing Separator Roll>
In the method shown exemplarily, a wholly aromatic polyamide (aramid resin) is used as a coating material which forms the heat-resistant layer 4. The method includes a step of disposing the heat-resistant layer 4 on the original sheet of the separator 12 (such an original sheet hereinafter also referred to as a “separator original sheet”).
Specifically, the method includes a first inspection step S11, a coating step S12, a depositing step S13, a cleaning step S14, a drying step S15, a second inspection step S16, a slitting step S17, and a winding step S18. Each of the steps S11 through S18 will be discussed below in order.
(First Inspection Step)
The first inspection step S11 is a step of inspecting the separator original sheet, which will serve as the base material of the heat-resistant separator 12a, in order to determine, prior to subsequent steps, whether or not there is a defect in the separator original sheet.
(Coating Step)
The coating step S12 is a step of coating, with a coating material (a material) for the heat-resistant layer 4, the separator original sheet which has been inspected in the first inspection step S11. In the coating step S12, it is possible to carry out the coating with respect to only one surface of the separator original sheet or both surfaces of the separator original sheet.
For example, in the coating step S12, the separator original sheet is coated with an aramid/NMP (N-methyl-pyrrolidone) solution, as the coating material for the heat-resistant layer 4. Note that the heat-resistant layer 4 is not limited to an aramid heat-resistant layer. For example, a mixed solution containing a filler such as alumina/carboxymethyl cellulose can be applied as the coating material for the heat-resistant layer 4.
A method for coating the separator original sheet with the coating material is not specifically limited as long as uniform wet coating can be performed with respect to the separator original sheet by the method, and various methods can be employed.
For example, it is possible to employ any of the methods such as a capillary 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.
A coating material for the heat-resistant layer 4 with which material the separator original sheet is coated has a film thickness that can be controlled by adjusting a thickness of a coating wet film and a solid-content concentration in the coating solution.
(Depositing Step)
The depositing step S13 is a step of solidifying the coating material with which the separator original sheet has been coated in the coating step S12. In a case where the coating material is an aramid coating material, for example, water vapor is applied to a coated surface so that aramid is solidified by humidity deposition.
(Cleaning Step)
The cleaning step S14 is a step of cleaning the separator original sheet on which the coating material has been solidified in the depositing step S13 (such a separator original sheet hereinafter also referred to as a “heat-resistant separator original sheet”). In a case where the heat-resistant layer 4 is an aramid heat-resistant layer, for example, water, an aqueous solution, or an alcohol-based solution is suitably used as a cleaning liquid.
Note that the cleaning step S14 can be multistage cleaning in which cleaning is carried out a plurality of times in order to enhance a cleaning effect.
Moreover, after the cleaning step S14, a water removing step can be carried out for removing water from the heat-resistant separator original sheet which has been cleaned in the cleaning step S14. A purpose of the water removing is to remove water or the like that is adhered to the heat-resistant separator original sheet before the subsequent drying step S15 so that drying can be carried out more easily and insufficient drying can be prevented.
(Drying Step)
The drying step S15 is a step of drying the heat-resistant separator original sheet that has been cleaned in the cleaning step S14. A method for drying the heat-resistant separator original sheet is not particularly limited, and, for example, it is possible to use various methods such as a method in which the heat-resistant separator original sheet is brought into contact with a heated roller or a method in which hot air is blown onto the heat-resistant separator original sheet.
(Second Inspection Step)
The second inspection step S16 is a step of inspecting the heat-resistant separator original sheet which has been dried in the drying step S15. In the inspection, a defect is marked as appropriate, and it is therefore possible to effectively inhibit the heat-resistant separator original sheet from having a defect.
(Slitting Step)
The slitting step S17 is a step of slitting (cutting) the heat-resistant separator original sheet which has been inspected in the second inspection step S16 into parts each having a predetermined product width. Specifically, in the slitting step S17, the heat-resistant separator original sheet is slit into parts each having a product width which is suitable for an applied product such as the lithium-ion secondary battery 1.
As described above, in order to increase productivity, a heat-resistant separator original sheet is usually produced so as to have a width that is equal to or greater than the product width. The heat-resistant separator original sheet 12a is therefore obtained by slitting the separator original sheet, in the slitting step S17, so as to have the product width.
(Winding Step)
The winding step S18 is a step of winding the heat-resistant separator original sheet 12a, which has been slit in the slitting step S17 so as to have the product width, around the core 5 having a cylindrical shape. In Embodiment 2, the core 5 which has been cleaned via the method for cleaning as described in Embodiment 1 is reused. This makes it possible to prevent (i) adherence of a foreign object to the heat-resistant separator 12a and (ii) damage to the heat-resistant separator 12a, each of which could occur in a case where the core 5 is not cleaned after use and is reused as is. This makes it possible to prevent the occurrence of product defects, such as short-circuiting, in a lithium-ion secondary battery 1 produced using the heat-resistant separator 12a.
In this way, the method for producing the separator roll 6 in accordance with Embodiment 2 includes the winding step S18 of winding the heat-resistant separator 12a around the core 5 which has been cleaned via the method for cleaning in accordance with Embodiment 1.
As such, Embodiment 2 makes it possible produce the separator roll 6 which can prevent, in reuse of the core 5, (i) adherence of a foreign object to the heat-resistant separator 12a and (ii) damage to the heat-resistant separator 12a.
[Supplemental Remarks]
A method for cleaning a separator core in accordance with an embodiment of the present invention is a method for cleaning a separator core having an outer peripheral surface around which a nonaqueous electrolyte secondary battery separator is to be wound, the method including: an end face cleaning step of removing a foreign object adhered to an end face of the separator core.
In a separator core which has been used and from which a separator (nonaqueous electrolyte secondary battery separator) has been wound off, there are cases in which a foreign object, such as an electrically conductive foreign object, is adhered to the separator core. Such a foreign object is particularly likely to adhere to an end face of the separator core. In the above method, a foreign object adhering to an end face of the separator core is removed in an end face cleaning step. This makes it possible to prevent a foreign object from adhering to a separator wound around the separator core when the separator core is reused.
As such, with the above method, it is possible to realize a method for cleaning the separator core which can suitably prevent, in reuse of the separator core, adherence of a foreign object to a separator.
The method for cleaning a separator core in accordance with an embodiment of the present invention preferably further includes an unevenness inspection step of inspecting the separator core in order to determine whether or not there is damage to the outer peripheral surface.
Since a cutter or the like may be used when cutting a separator off from the separator core, there is the risk that there will be damage present in the outer peripheral surface of the separator core after the separator core has been used. In a case where the separator core having such damage is reused as is, unevenness caused by the damage can damage a separator wound around the separator core. This can cause a product defect such as a short circuit in a nonaqueous electrolyte secondary battery produced using the separator.
In the above method, the separator core is inspected, in the unevenness inspection step, in order to determine whether or not there is damage to the outer peripheral surface of the separator core. This makes it possible to avoid reusing the separator core in a state where there remains damage to the outer peripheral surface thereof. This, in turn, makes it possible to prevent a separator which is to be wound around the separator core from being damaged by unevenness due to such damage to the separator core.
The method for cleaning a separator core in accordance with an embodiment of the present invention preferably further includes a damage repair step of, in a case where damage to the outer peripheral surface is found in the unevenness inspection step, repairing the damage.
In the above method, damage to the outer peripheral surface of the separator core is removed in the damage repair step. This makes it possible to prevent unevenness caused by the damage from damaging a separator when the separator core is reused.
The method for cleaning a separator core in accordance with an embodiment of the present invention preferably further includes an outer peripheral surface cleaning step of removing a foreign object adhered to the outer peripheral surface.
In the above method, a foreign object adhering to the outer peripheral surface of the separator core is removed in the outer peripheral surface cleaning step. This makes it possible to prevent the foreign object adhering to the outer peripheral surface from adhering to a separator when the separator core is reused.
The method for cleaning a separator core in accordance with an embodiment of the present invention preferably further includes a whole core cleaning step of wiping a whole of the separator core with a fiber member.
In the above method, the whole of the separator core is wiped with the fiber member in the whole core cleaning step. This makes it possible to reliably remove a foreign object adhering to the separator core.
The method for cleaning a separator core in accordance with an embodiment of the present invention is preferably arranged such that, in the end face cleaning step, a pressure-contact member is pressed into contact with the end face.
With the above method, it is possible to better prevent deterioration of the separator core, in comparison to a method in which, for example, a solvent such as alcohol is used to clean an end face of the separator core.
The method for cleaning a separator core in accordance with an embodiment of the present invention is preferably arranged such that the pressure-contact member is in the form of a sheet.
The above method makes it possible to suitably remove a foreign object adhering to an end face of the separator core by scouring off the foreign object with the pressure-contact member in the form of a sheet.
The method for cleaning a separator core in accordance with an embodiment of the present invention is preferably arranged such that the pressure-contact member has asperities or a plurality of micropores.
In the above method, the pressure-contact member in the form of a sheet has asperities or a plurality of micropores. This makes it possible to increase the wiping effect of the pressure-contact member in the form of a sheet.
The method for cleaning a separator core in accordance with an embodiment of the present invention is preferably arranged such that in the end face cleaning step, a liquid which has been accelerated is caused to impact the end face.
The above method makes it possible to more easily remove a foreign object adhering to an end face of the separator core.
The method for cleaning a separator core in accordance with an embodiment of the present invention is preferably arranged such that in the end face cleaning step, the end face is treated with a solvent which is aprotic.
With the above method, it is possible to better prevent deterioration of the separator core, in comparison to a method in which, for example, alcohol is used to treat an end face of the separator core.
The method for cleaning a separator core in accordance with an embodiment of the present invention is preferably arranged such that in the end face cleaning step, the end face is treated with a liquid obtained by adding a surfactant to water.
With the above method, it is possible to better prevent deterioration of the separator core, in comparison to a method in which, for example, alcohol is used to treat an end face of the separator core.
The method for cleaning a separator core in accordance with an embodiment of the present invention preferably further includes a foreign object inspection step of inspecting the separator core which has been cleaned in the end face cleaning step, in order to determine whether or not a foreign object is adhered thereto, the inspecting being carried out under lighting having (i) a color temperature in a range from 2500 K to 7000 K and (ii) a special color rendering index R15 of not less than 60.
With the above method, black electrically conductive material or white material that has adhered to the separator core is adequately visible. As such, in a case where such black electrically conductive material or white material has adhered to the separator core as foreign object, the above method makes it easy to quickly find such a foreign object. As such, with the above method, it is possible to shorten the amount of time of an inspection step required for reuse of the separator core.
A separator roll in accordance with an embodiment of the present invention includes: a separator core which has been cleaned by the method for cleaning in accordance with an embodiment of the present invention; and a nonaqueous electrolyte secondary battery separator wound around the separator core.
The above configuration makes it possible to realize a separator roll which makes it possible to prevent, in reuse of the separator core, (i) adherence of a foreign object to a separator and (ii) damage to the separator.
A method for producing a separator roll in accordance with an embodiment of the present invention includes: a winding step of winding a nonaqueous electrolyte secondary battery separator around a separator core which has been cleaned by the method for cleaning in accordance with an embodiment of the present invention.
With the above method, it is possible to realize a method for producing a separator roll which makes it possible to prevent, in reuse of the separator core, (i) adherence of a foreign object to a separator and (ii) damage to the separator.
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. The present invention also encompasses, in its technical scope, any embodiment derived by combining technical means disclosed in differing embodiments. Further, it is possible to form a new technical feature by combining the technical means disclosed in the respective embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-130288 | Jun 2016 | JP | national |
| 2016-250240 | Dec 2016 | JP | national |
