JPS5821775B2 - Denchiyo Fushiyokufu Separator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a multilayer battery with uniform porosity that prevents the movement of electrode fragments and oxides generated during battery use, and allows charged ions and electrolyte to freely pass through. This invention relates to a nonwoven fabric separator for batteries.

Characteristics required for battery separators include good electrolyte retention and high liquid absorption speed, prevention of debris and oxide powder from escaping from electrodes, and prevention of gases and charged ions passing through. It is required that the material is not obstructed, has no through holes, has uniform porosity, and has a small internal resistance (G').

Conventionally, battery separators to meet these requirements have been made by hot-pressing a mixed web of high-melting point and low-melting point polyamide fibers or a single web of thermoplastic fibers with heated rolls to fuse the fibers together at their melting points and crossing points. However, the aforementioned battery separators use so-called heat-sealable fibers, whose entire fibers are made of low-melting-point resin, as a nonwoven fabric binder, so they soften and melt during hot pressing, causing damage to the surface of the rolls. The fibers on the upper and lower surfaces of the web that are in contact tend to melt and form a film due to direct heat and pressure, forming a film with a smooth surface, and the surface layer is much more dense and clogged than the inner layer.

In addition, when using the latter, a web made solely of thermoplastic fibers, hot pressing must be carried out at high temperatures and pressures up to the melting point of the fibers61, and when hot pressing is carried out at a temperature lower than the melting point, the fibers must be heated in the same way as a roll. There is a method of hot pressing a web arranged parallel to the direction, but since the fibers are arranged in parallel and have directionality, workability and resistance are poor, and there are disadvantages in that uniformity in the thickness direction cannot be obtained.

In any case, the surface layer of the nonwoven fabric separator obtained by fusing the fibers together under high temperature and high pressure becomes a film due to the high pressure, which increases the gloss and inevitably causes much more clogging on the surface than the inner layer. It tends to become dense and has the disadvantage that the porosity is not uniform in the thickness direction.

Therefore, all of these devices have the disadvantage that electrode fragments or oxides in the electrolyte adhere only to the surface of the separator, causing clogging and blocking the passage of gas or ions, which adversely affects battery life and efficiency. .

The present invention has been made to solve such conventional problems and satisfy the above conditions, and the upper and lower outer layers of the separator are made of fibers having a finer degree than the inner layer or dog fibers having the above fineness. A web with a sandwich structure is prepared by heating and processing a sandwich-structured web consisting of a fiber layer in which at least one of the inner layers is made of fibers with a smaller fineness than the outer layer, or mixed fibers with the above-mentioned fibers with a smaller fineness as the main layer. The separator is characterized in that the porosity of the inner and outer layers of the separator is made uniform by taking advantage of the tendency of the outer layer to be heated, pressed and densified more than the inner layer. .

Next, the configuration of the present invention will be explained with reference to the drawings.

! The fiber material used in the nonwoven fabric separator for batteries of the present invention is generally selected from fibers that have chemical resistance to electrolytes, and fibers such as polyethylene, polypropylene, polyvinyl chloride, polyamide, and Teflon are used, but in some cases. Two.

In some cases, these fibers are also mixed.

These fibrous materials are used in the same way as in normal nonwoven fabric manufacturing.
A fibrous web is formed by mixing cotton, opening, and developing into a sheet.

This fibrous web is bonded and fixed to constitute a uniformly porous non-woven fabric.

Composite heat-fusible fibers such as heat-fusible nylon-polypropylene, polyethylene-polypropylene, etc., which are bonded only at the contact surfaces of the fibers at their intersection points and melting points, are mixed in advance.

Figure 1 shows the structure of the base fiber layer of the nonwoven fabric separator of the present invention using the above-mentioned fibers, and the outer layers 2 and 3 are composite heat-sealed with thermoplastic fibers of 3 denier or more, which have a larger fineness than the inner layer. The inner layer 1 is composed of mixed fibers with thermoplastic fibers, or is composed of thermoplastic fibers and composite heat-sealable fibers mainly composed of thermoplastic fibers with different finenesses, and the inner layer 1 has a slightly smaller fineness than the outer layer 2. , consisting mainly of thermoplastic fibers of 5 deniers or less and mixed with heat-fusible fibers, or composed mainly of thermoplastic fibers with thermoplastic fibers of different fineness and composite heat-fusible fibers.

And got it. The fiber layer of the sand inch structure is then hot-press molded by continuous press using heated rolls, or if heat and pressure are applied from the outer layer, the outer layer 2 is more dense than the inner layer 1.
．． Therefore, as shown in Figure 2, the difference in fiber weave in the inner layer 1a, outer layers 2a, and 3a causes the fibers to form in the cross-sectional layer, that is, between the fibers in the thickness direction. The gaps (voids) are made uniform.

It has been found that in order to make the pore spaces uniform, the difference between the fineness of the inner layer fiber and the outer layer fiber must be approximately 0.5 to 3 deniers.

In addition, when using a separator with a fineness of 1 to 3 denier to avoid through-holes in the thickness direction, the fiber basis weight should be 50 g / m or more, and the apparent density should be 0.2 under pressure and heating conditions. It is preferable to mold it so that it becomes 0.45 g/cc.

Figures 3 and 4 show another configuration, in which a fiber layer 5 with a small fineness and a fiber layer with a large fineness as a thickness adjustment layer 4 are added in the middle, and are formed by thermo-pressure molding. , the porosity is more uniform than the structure shown in FIG. 2, and the number of through holes can be reduced.

With this multilayer structure, the porosity and density of each fiber layer in the thickness direction are almost indistinguishable.

Generally speaking, it is difficult to prevent the generation and movement of electrodes, debris, and oxides during the process of use of battery separators, and even the presence of even a small through hole can adversely affect battery characteristics. A separator with as high precision as possible is required, and in order to further improve the electromotive force, it is necessary to further reduce the gap between the electrode plates of the battery. It is required to be thin, porous, and have a uniform thickness with no unevenness.In order to satisfy this purpose, the more the number of layers of fiber layers with relatively large fineness and fiber layers with relatively small fineness increases, the more uniform the thickness will be. , giving more stable battery characteristics.

To manufacture these nonwoven fabric separators, it is preferable to heat a fibrous web mixed with composite heat-fusible fibers to a temperature above the softening melting temperature of the heat-fusible fibers, and then press and fix the fiber web with a cooling roll. If problems occur such as the roll losing its shape or sticking to the roll and causing fuzz,
In advance, the surface of the fiber web is lightly bonded with a resin binder having a higher melting point than the heat-sealable fibers, which has resistance to the electrolyte, and which does not deteriorate battery characteristics.

The resin binder is applied by spraying or dipping to an extent that does not form a surface film, that is, a small amount of 10 parts or less is applied to the fibers.

Next, it is manufactured by pressurizing it with a hot roll (roll temperature set near the melting point of the heat-sealable fiber).

The present invention also includes products produced as described above.

Furthermore, the details will be explained using examples.

Example 1 Using three card machines A, B, and C, A and C cards are each made of polypropylene.
0 parts polyethylene 0 lopyrene 2 parts 5 /mrrdyt 10 parts polyethylene, polypro composite fiber (MP14ω-145°C) 3 denier 64 pieces cut
30 parts fiber web date 25g/m" B card machine's fiber blend is polypropylene 2 dens 51m young cut 60 parts polypropylene 3 dens 51m cut 10
Part polyethylene, polypro composite fiber (MP140-145°C)
The above carded web formed with a fiber layer of 30 parts fiber web date 25g/m was passed through carding machine A.
, B, and C are stacked in the order of 115 to form a sandwich.
As shown in FIG. 2, the outer layer 2a is separated from the inner layer 1a by passing through a hot press roll kept at 0° C. and fixed under heat.

Since the 3a side is easily clogged, this combined with the difference in fineness between the inner and outer layers resulted in a sandwich-like nonwoven fabric separator having a porous structure with uniform fiber gaps in the thickness direction.

The thus obtained separate lake had a thickness of 0.22 mm, a basis weight of 75 g/i, and an apparent density of 0.34 g/cffl.

Next, a comparative example will be shown to clarify the difference with conventional products.

Comparative Example 6 Nylon fiber 2 denier 51 mm cut 50% P6 nylon fiber 3 denier 51 basket cut 50% mixed fiber web with fiber basis weight 80 g / rrl: was immersed in a zinc chloride solution, which is a fiber solvent, and the fiber surface was After soaking for a certain period of time at a temperature that slightly dissolves S, the excess liquid is squeezed out and the dissolved fibers are impregnated with a liquid that is compatible with the solvent, but is a non-solvent. At the same time as bonding between the fibers, the solvent was extracted and the washed product was heated to 100 to 100 kg.Then, it was hot pressed with a roll heated to 145°C to give a fabric weight of 80.
The surface of the product having a g/rrl and a thickness of 0.20 to 0.25 mm was shiny and formed into a film.

Next, the characteristic values of the product of the present invention and the above comparative example were measured and shown in the table below.

As a result, it was found that the separator of the present invention having a sandwich structure having a difference in outer layer fineness has a small coefficient of variation in weight, liquid content, and air permeability, and has good precision and excellent uniformity.

Example 2 Using five card machines A, B, (ill', D, and E)
.

The fiber composition of C and E card machines are respectively polypropylene 7-technical 511 mt 15
Polypropylene 3 parts - 1151 mg 1 part
55 parts polyethylene, polypro composite fiber (MP14α~145°C) 3 pieces/L/64m ribs 30 parts each, fiber web weight 16
Form a web of g/m'.

On the other hand, the fiber composition of B and D card machines is nylon 3 denier 51 mm thick 15
Nylon 2 lengths 38 mrrrht
65 parts polyethylene, polypro composite fiber (MP14ω~145°C) 3 strands h4mrtrh
A web consisting of 20 parts each having a fiber basis weight of 16 g/m' is produced.

A card web having the above fiber composition is processed by card machine ABC.
A card web laminated in the order of DE was impregnated with a 1.2 ratio aqueous solution of polyvinyl alcohol (D = 1700) and dried to produce a nonwoven fabric with a solid coverage of 5 ratio.

The thickness of this product was 79 g/m with a three-way mark. When this was hot-pressed at a speed of 2.4 m/m using a roll heated to 150°C, a uniform porous film with a thickness of 0.22 mrn to 0.25 mm was obtained. A nonwoven separator was obtained.

Compared to conventional products, the surface has less gloss and the fluctuation coefficient of air permeability has been reduced to approximately A.

Therefore, in the nonwoven fabric separator according to the present invention, since the total fiber length per unit volume is about 10 to 20 times longer in the inner layer, the surface density does not increase more than the inner layer even by the heat and pressure that are mostly applied to the outer layer. In addition, the inner and outer layers have a multilayer structure with different fineness, resulting in excellent uniformity, and the structure has no through holes in the thickness direction, making it easier for charged ions to pass through, preventing electrode fragments and oxidation. It can prevent the movement of powder particles, exhibit stable battery characteristics, and at the same time exhibit many effects such as further improving the service life of the battery.

[Brief explanation of the drawing]

1 to 4 show the structure of a nonwoven fabric separator for batteries according to an embodiment of the present invention, and FIG. 1, FIG. 3, and FIG. FIG. 4 is a sectional view showing the structure of the nonwoven fabric separator after molding. 2, 3, 2a, 3a...outer layer (fiber layer with fineness), 1.5.1a, 5a...inner layer (
(fiber layer with small fineness), 4, 4a... adjustment layer (fiber layer with small fineness).

Claims (1)

[Claims] 1 Having a sandwich structure in which three or more layers of a mixed fiber web of a composite heat-sealable fiber having a low melting point component that is chemically resistant to electrolytes and a high melting point organic synthetic fiber are laminated, and the outer layer constituent fibers of the sandwich structure are is made of a fiber web mainly composed of fibers that are all larger in fineness than the fibers that make up the inner layer or have the fineness above, and at least one of the inner layers is made of fibers that are all smaller in fineness than the fibers that make up the outer layer or have a fineness that is smaller than the above fineness. A nonwoven fabric separator for batteries, characterized in that it is composed of a fibrous web mainly composed of fibers, and has an integrally molded uniform porous structure with a difference in fineness between the inner layer and the outer layer fibers of 0.5 to 3 deniers.