JP2015046288A - Method of manufacturing separator for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a separator for lithium ion secondary battery which allows for stable production of a long separator, where the coating liquid distribution of coating liquid is uniform and the battery characteristics are excellent, even if the base material is thin.SOLUTION: A method of manufacturing a separator for lithium ion secondary battery by giving a coating liquid, containing inorganic particles or organic particles, to a base material includes a step for squeezing the coating liquid by means of at least two vent blades after the coating liquid is carried on the base material, and the length of the bent blades are different from each other.

Description

  The present invention relates to a method for producing a separator for a lithium ion secondary battery (hereinafter sometimes abbreviated as “separator”).

  With the recent spread of portable electronic devices and higher performance, secondary batteries having high energy density are desired. As this type of battery, a lithium ion secondary battery using an organic electrolyte (non-aqueous electrolyte) has attracted attention. Since non-aqueous electrolytes are flammable, there is a risk of ignition and the like, and careful attention is paid to safety in their use.

  The porous film made of polyolefin such as polyethylene, which is often used as a separator, melts and closes the micropore when the temperature inside the battery is around 130 ° C. There is a thermal fuse function (shutdown function) that shuts off the power. However, it has been suggested that if the temperature further increases due to some situation, the polyolefin itself may melt and short-circuit, causing thermal runaway. In order to prevent such a short circuit due to thermal contraction of the separator, a separator in which inorganic particles or organic particles are applied to a base material has been proposed. As the substrate, a porous film made of polyolefin may be used, or a non-woven fabric with good heat resistance may be used.

  As a method for producing such a separator, a liquid containing inorganic particles or organic particles (hereinafter also referred to as “coating liquid”) is applied to a base material, and then a predetermined peripheral speed in a direction opposite to the transport direction of the base material. By passing the base material between two rolls arranged so that the straight line connecting the rotation axes of each other rotated at right angles to the traveling direction of the base material, the excess coating liquid on the base material is removed, A proposal has been made to make the surface of the coating film uniform (see, for example, Patent Document 1).

  Further, a roll that rotates in a direction opposite to the traveling direction of the base material is brought into contact with only one side of the base material, or a plurality of rolls that rotate in a direction opposite to the traveling direction of the base material, By sequentially bringing both surfaces of the base material into contact with a plurality of rolls arranged so that the straight lines connecting the rotation axes of the rolls facing the base material are not orthogonal to the traveling direction of the base material, There has also been a proposal to make the thickness of the film uniform (see, for example, Patent Document 2).

  However, according to the techniques of Patent Documents 1 and 2, the coating amount distribution of the coating liquid tends to be non-uniform in the width direction, pinholes and high resistance portions exist in the separator, and the ion permeability becomes non-uniform. It was difficult to obtain a separator with good battery characteristics. Furthermore, when the base material is thin, wrinkles enter the base material, resulting in coating spots, and it is difficult to continuously produce a long separator with high thickness uniformity.

JP 2002-166218 A JP 2008-179903 A

  An object of the present invention is to provide a separator for a lithium ion secondary battery that can produce a long and stable separator even when the substrate is thin, with a uniform coating amount distribution of the coating liquid and good battery characteristics. It is in providing the manufacturing method of.

As a result of intensive studies to solve the above problems, the present inventors have
(1) A method for producing a separator for a lithium ion secondary battery in which a coating liquid containing inorganic particles or organic particles is applied to a base material, and at least two sheets after the coating liquid is supported on the base material A method for producing a separator for a lithium ion secondary battery, characterized in that it has a step of squeezing the coating liquid with a vent blade of the above, and the length of each vent blade is different,
(2) The manufacturing method of the separator for lithium ion secondary batteries as described in (1) whose base material is a nonwoven fabric,
I found.

  With the method for manufacturing a separator for a lithium ion secondary battery according to the present invention, a separator having a uniform coating amount distribution and good battery characteristics can be produced stably in a long length even when the substrate is thin. It is possible to manufacture a lithium ion secondary battery separator that does not have pinholes or high resistance.

It is the schematic which showed an example of the one part process concerning the manufacturing method of the separator for lithium ion secondary batteries in this invention. It is explanatory drawing regarding the vent blade which squeezes the coating liquid of the apparatus concerning the manufacturing method of the separator for lithium ion secondary batteries in this invention. It is sectional drawing regarding the vent blade which squeezes the coating liquid of the apparatus concerning the manufacturing method of the separator for lithium ion secondary batteries in this invention.

  Hereinafter, the manufacturing method of the separator for lithium ion secondary batteries of this invention is demonstrated, using drawing. In FIG. 1 to FIG. 3, dotted arrows indicate the conveyance direction of the substrate 2.

  FIG. 1 is a schematic view showing an example of a part of steps relating to a method for producing a separator for a lithium ion secondary battery in the present invention. First, the base material 2 is supported on the base material 2 while the base material 2 is pulled out and conveyed from the base material roll 3 around which the base material 2 is wound. The method for supporting the coating liquid on the base material 2 is not particularly limited. For example, as shown in FIG. 1, a method of passing the base material 2 through the impregnation pad 5 containing the coating liquid is used. Can do. In FIG. 1, reference numeral 4 denotes an impregnation roll.

  Next, with the at least two vent blades 1 having different lengths, the supporting amount of the coating liquid on the base material 2 is uniformly adjusted leaving a necessary amount so as to sandwich the base material 2. By changing the length of the vent blade 1, one surface of the base material is first smoothed by the short side vent blade 1, and then the opposite surface of the base material is smoothed by the long side vent blade 1. FIG. 2 is an explanatory diagram regarding two vent blades having different lengths for squeezing the coating liquid of the apparatus according to the method for manufacturing a separator for a lithium ion secondary battery in the present invention. FIG. 3 is a cross-sectional view of two vent blades having different lengths for squeezing the coating liquid of the apparatus according to the method for manufacturing a separator for a lithium ion secondary battery in the present invention. The vent blades 1 having different lengths can control the clearance with the blade profiler bar 8 in the width direction, and can finely adjust the amount of coating liquid carried. The surplus coating liquid falls on the impregnation pad 5 and is circulated. Next, the base material 2 whose surface is smoothed is dried by a dryer 7 through a transport roll 6 and wound up by a reeler. 1 to 3, the coating liquid is squeezed by two vent blades 1 having different lengths, but the number of vent blades 1 having different lengths may be three or more.

  In the present invention, the material of the vent blade is not particularly limited, and various resins such as polyester, polypropylene, soft vinyl chloride resin, low foam vinyl chloride resin, fluororesin, acrylic resin, ABS (acrylonitrile butadiene styrene copolymer) resin, polycarbonate, etc. It is preferable to appropriately select materials such as plates, aluminum, iron, copper, steel, various metal plates such as SUS, and other carbon fiber plates according to the type of coating liquid used. Further, in the case of an aqueous coating solution, the contact surface of the vent blade with the coating solution is preferably hydrophobic because of the effect of suppressing the occurrence of lateral steps due to friction. In the case of hydrophilicity, it is preferable to perform a hydrophobizing treatment as necessary. You may coat | cover the material (For example, a ceramic, a metal oxide, a metal carbide etc.) which is hard to wear as needed.

  In the present invention, it is preferable that the thickness of the vent blade is appropriately selected from 0.1 mm to 2 mm depending on the apparatus width. Since the vent blade is used with the blade being largely distorted, it is preferable to change the thickness appropriately according to the material of the vent blade. Since the distortion of the vent blade is large, the pressure distribution in the width direction becomes more uniform as the force in the width direction increases. Moreover, the vent blade can adjust the coating amount on both sides of the substrate and in the width direction with a blade profiler bar, if necessary. The blade profiler bar is preferably installed at a position 3/4 to 1/2 from the base of the vent blade. Also. The position of the blade profiler bar can be adjusted as appropriate depending on the material, thickness, and hardness of the vent blade.

  In this invention, although the width | variety of a vent blade is suitably adjusted according to a base-material width, it is preferable to set 10-20 mm wider than a base-material width.

  In the present invention, the length of the vent blade is preferably approximately twice the horizontal distance from the base of the vent blade to the base material, preferably 40 to 70 mm, more preferably 50 to 60 mm. preferable. The at least two vent blades should have a length difference of 1 to 20 mm, preferably 2 to 10 mm, more preferably 3 to 8 mm.

  In the present invention, a double-sided vent blade composed of at least two vent blades having different lengths so as to be sandwiched between the base material and the vent blade has a blade edge of 1 to 20 mm, preferably 2 to 10 mm, more preferably A separator having a uniform coating amount and a beautiful coating surface can be produced by installing the nozzles so as to be shifted by 3 to 8 mm and matching the widths and squeezing the coating liquid on both sides.

  In the present invention, by changing the length of the vent blade, the conveyance direction of the base material can be angled to the vent blade side longer than the vertical direction, and wrinkles generated by pulling in the vertical direction are suppressed. be able to. Moreover, the smoothness of the substrate surface is improved, and the generation of pinholes can be suppressed.

  In the present invention, examples of the substrate include porous films, nonwoven fabrics, woven fabrics, and woven fabrics. As a porous film, porous films, such as polyethylene, a polypropylene, an olefin, an aramid, a polyimide, a fluorine, can be used. The porous film may be a single layer or a multilayer of two or more layers. In the case of multiple layers, porous films of the same kind of material may be stacked, or films of different kinds of materials may be used in combination. Further, the porous film may contain fibers, inorganic fillers, organic fillers, and the like.

  In the present invention, the base material is preferably a nonwoven fabric in order to improve heat resistance or reduce the internal resistance of the lithium ion secondary battery. Non-woven fabric is not particularly limited, but polyolefin resin, polyester resin, polyamide resin, acrylic resin, polyvinyl ether resin, polyvinyl ketone resin, polyether resin, polyurethane resin, unsaturated resin Nonwoven fabrics containing fibers such as polyester resins and fine cellulose can be used. These fibers can be incorporated not only in one type but also in a mixture.

  The thickness of the substrate is preferably 6 μm or more, more preferably 8 μm or more, and further preferably 10 μm or more in order to ensure the strength as a separator. Moreover, 30 micrometers or less are preferable from the surface of a battery characteristic, 20 micrometers or less are more preferable, and 15 micrometers or less are further more preferable. In this invention, even if it is a thin base material of 6-30 micrometers, the separator for lithium ion secondary batteries can be produced stably long.

The basis weight of the substrate is preferably 6 g / m ² or more, more preferably 7 g / m ² or more, and even more preferably 8 g / m ² or more in order to ensure the strength as a separator. . Moreover, from the surface of a battery characteristic, 20 g / m < ² > or less is preferable, 15 g / m < ² > or less is more preferable, and 12 g / m < ² > or less is more preferable.

The density of the base material, in order to sufficiently ensure the ion permeability, preferably from 0.85 g / cm ³ or less, preferably further 0.75 g / cm ³ or less, 0.70 g / cm ³ or less is most preferred. Moreover, it is difficult to obtain smoothness of the substrate, 0.30 g / cm ³ or more, more preferably more 0.40 g / cm ³ or more, 0.45 g / cm ³ or more is most preferable. In the present invention, the density is a value obtained by dividing the basis weight of the substrate by the thickness of the substrate.

Inorganic particles used in the present invention include, but are not limited to, _{boehmite, SiO 2, Al 2 O 3} , alumina - may be used silica composite oxide.

  The organic particles used in the present invention are not particularly limited, and examples thereof include SBR (styrene-butadiene rubber) resins, acrylic resins, cellulose derivatives, and fluorine resins.

  The medium for the coating liquid in the present invention is not particularly limited, but water or an organic medium can be used. Examples of the organic medium include a solvent having a hydroxyl group such as methanol, ethanol and isopropyl alcohol, and a medium having a carbonyl group such as acetone and methyl ethyl ketone.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a present Example.

Example 1
A microporous polyethylene (PE) film (basis weight: 10 g / m ² , thickness: 18 μm, width: 250 mm) was prepared as the base material 2, and a lithium ion secondary battery separator was manufactured. The first of the two vent blades 1 is a high-density polyethylene film (thickness 0.2 mm, width 300 mm, length 100 mm), and the second is a high-density polyethylene film (thickness 0.2 mm, width 300 mm, length 104 mm). ) Were respectively placed on both sides of the base material 2 so as to sandwich the base material 2 therebetween. The blade profiler bar 8 is located at a position of 24 mm (first vent blade 1) and 28 mm (second vent blade 1) from the cutting edge of the vent blade 1, and the position of the blade profiler bar 8 is the same with the base material 2 interposed therebetween. It was adjusted and attached so that

  After transporting the base material 2 and immersing it in an impregnation pad 5 containing a coating liquid containing boehmite and an acrylic resin to carry the coating liquid on the base material, two vent blades having different lengths are used. In step 1, the coating solution was uniformly squeezed to increase the smoothness of the substrate surface, and the coating amount was adjusted. Next, it was dried with a dryer 7 to produce a separator for a lithium ion secondary battery.

Example 2
A separator was produced in the same manner as in Example 1 except that the base material 2 was a non-woven fabric (basis weight 8 g / m ² , thickness 15 μm, width 250 mm) made of long polyethylene terephthalate (PET).

Comparative Example 1
As the vent blade 1, two high-density polyethylene films of the same size (thickness 0.2 mm, width 300 mm, length 100 mm) are used, the edge of the vent blade 1 is aligned, and the position of the blade profiler 8 sandwiches the base material 2. A separator was manufactured in the same manner as in Example 1 except that the adjustment was made to be the same.

Comparative Example 2
A separator was produced in the same manner as in Example 1 except that the coating liquid was squeezed using a SUS roll (φ30 mm, width 300 mm, clearance 0.1 mm) instead of the vent blade 1.

<Evaluation>
The following evaluation was performed about the separator for lithium ion secondary batteries obtained by the Example and the comparative example, and the result was shown in Table 2.

[Separator film thickness]
For the manufactured separator, measurement was made at 20 locations using a contact-type film thickness meter (Mitutoyo, contact terminal is cylindrical with a bottom of 5 mm in diameter), and the difference between the maximum value and the minimum value was less than 2 μm. 2 μm or more and less than 3 μm is represented by “Δ”, and 3 μm or more is represented by “x”.

[Separator basis weight]
About the produced separator, it cut into 200 mm x 250 mm angle | corner, measured mass using the electronic balance (the product made from METLER, AJ150), and made 20 times the basic weight (g / m < ² >).

[Presence of wrinkles]
About the produced separator, the presence or absence of wrinkles was confirmed visually. Those with no wrinkles in the width of 250 mm are indicated with “◯”, those with 1 or more and 3 or less confirmed “Δ”, and those with 4 or more confirmed with “x”.

[Visual evaluation of separator surface quality]
About the produced separator, the separator surface quality was confirmed visually. If the horizontal width (coating unevenness that can be made stepwise in the width direction of the base material), wrinkles (wrinkled vertical streaks), and streak (vertical streaky coating unevenness) are not within 10 meters in the width of 250 mm, “○” indicates that one or more and four or less are confirmed, and “×” indicates that five or more are confirmed.

[Separator impedance measurement]
In order to evaluate the uniformity of ion permeability, impedance measurement was performed. Using 1M LiPF ₆ / EC: DEC (30:70 vol%) as the electrolyte, incorporating the separators of each example and comparative example into a commercially available assembled battery evaluation cell, and measuring the impedance at 20 kHz for 20 samples. did. The difference between the maximum value and the minimum value was expressed as “◯”, the difference between 0.5Ω and less than 1.0Ω as “Δ”, and the difference between 1.0Ω and 1.0 as “×”. A portion where the film thickness is thick or a portion where the particles are densely packed has a large value because the ion movement distance between the electrodes becomes long. On the other hand, the portion where the film thickness is thin or the portion where the particle is coarsely filled has a small value because the ion movement distance becomes short. For this reason, a large difference between the maximum value and the minimum value means that the coating amount is non-uniform and the ion permeability is non-uniform.

[Separator pinhole detection]
In order to evaluate the presence or absence of pinholes in the separator, light was applied from the back of the separator, and the light transmission location was visually confirmed. “O” indicates that there is no transmission portion within a 200 mm × 200 mm square, “Δ” indicates that the transmission location is 1 to less than 10, and “X” indicates that the transmission location is 10 or more.

[Production of evaluation battery]
(1) A positive electrode agent paste composed of 89.5 parts by mass of lithium manganate powder, 4.5 parts by mass of acetylene black, 6 parts by mass of polyvinylidene fluoride (PVdF), and N-methylpyrrolidone as a solvent was 2.0 mAh / cm. A positive electrode plate having a thickness of 97 μm was obtained by applying, drying and pressing on an aluminum foil having a thickness of 20 μm so that a capacity of ² was obtained.
(2) A negative electrode agent paste composed of 87 parts by mass of mesophase carbon microbead powder, 3 parts by mass of acetylene black, 10 parts by mass of PVdF, and N-methylpyrrolidone as a solvent so that a capacity of 2.1 mAh / cm ² can be obtained. The coating was dried and pressed on a copper foil having a thickness of 18 μm to produce a negative electrode plate having a thickness of 90 μm.
(3) 1M LiPF ₆ / ethylene carbonate (EC): diethyl carbonate (DEC) (30:70 vol%) (manufactured by Kishida Chemical Co., Ltd.) was used as the electrolytic solution.
(4) As a separator, the separator produced by the Example and the comparative example was used.
(5) The positive electrode and the negative electrode (30 mm × 50 mm) were opposed to each other through a separator (40 mm × 60 mm). This was impregnated with an electrolytic solution and vacuum-sealed in an exterior made of an aluminum laminate film to produce a lithium ion secondary battery with a design capacity of 30 mAh. Five batteries were prepared for each separator.

[Battery characteristics: Separator C-rate discharge test (discharge capacity)]
The battery for evaluation was subjected to three-cycle aging at 1C, followed by constant current and constant voltage charge (1 / 10C cut) at 1C and 4.2V, and then a constant current discharge test (2.8V cut) at 5C. The average value of the discharge capacity was calculated. The unit is mAh.

  Table 1 summarizes the base materials used, the diaphragm means, and the materials of the diaphragm means in a list.

  Table 2 will be described in detail. In Examples 1 and 2, after the coating liquid is supported on the base material, the coating liquid excessively supported on the base material is scraped to an appropriate amount and squeezed by at least two vent blades having different lengths. By smoothing the surface of the substrate, it was possible to produce a separator with a beautiful coating surface, less wrinkles, less ion permeability, and fewer pinholes. In comparison between Examples 1 and 2, the separator performance was good, but Example 2 using a nonwoven fabric was slightly superior in battery characteristics.

  From the comparison between Examples 1 and 2 and Comparative Example 1, the effect of the difference in the length of the vent blade enables the surface quality of the separator to be good, there is no pinhole, adjustment to an appropriate thickness, and ion permeation is possible. It can be seen that there is little unevenness in properties and the generation of wrinkles can be suppressed. In Comparative Example 1, the separator was relatively good, but the surface quality of the separator was slightly inferior. From the comparison between Examples 1 and 2 and Comparative Example 2, the effect of the vent blade is that there is no pinhole, adjustment to an appropriate thickness is possible, there is little unevenness in ion permeability, and generation of wrinkles can be suppressed. Recognize. In Comparative Example 2, there were thickness unevenness, slight wrinkles, ion permeability unevenness, and slight pinholes, and there was a large difference in battery characteristics.

  The present invention can be suitably used as a method for producing a separator for a lithium ion secondary battery.

DESCRIPTION OF SYMBOLS 1 Vent blade 2 Base material 3 Base material roll 4 Impregnation roll 5 Impregnation pad 6 Transport roll 7 Dryer 8 Blade profiler bar 9 Smoothing roll

Claims (2)

  A method for producing a separator for a lithium ion secondary battery, wherein a coating liquid containing inorganic particles or organic particles is applied to a base material, wherein at least two vent blades are supported after the coating liquid is supported on the base material A method for producing a separator for a lithium ion secondary battery, comprising the step of squeezing the coating solution by using a different length of each vent blade.   The method for producing a separator for a lithium ion secondary battery according to claim 1, wherein the substrate is a nonwoven fabric.