JPH06101322B2 - Organic electrolyte battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a separator of an organic electrolyte battery (hereinafter referred to as a lithium battery) using an active light metal such as lithium as a negative electrode active material.

2. Description of the Related Art Lithium batteries, which have the excellent performance of high voltage and high energy density, have been used in various applications in recent years and are also used in various consumer devices. However, since an active light metal such as lithium is used as the active material, the safety of the battery is extremely important, and various methods have been studied. In particular, when the battery is short-circuited, there is a possibility that the internal temperature rapidly rises and the internal pressure rises, and the battery contents are ejected. Should such a situation occur, not only the battery but also the equipment using the battery will be damaged. Therefore, as an effective method to prevent this, the separator enclosing one electrode due to the temperature rise at the time of short circuit is melted, and the minute holes of the separator are closed to prevent the current from flowing between the electrodes, resulting in further It was considered to prevent the occurrence of the above-mentioned abnormal situation by suppressing the temperature rise of.

As a separator effective in this method, conventionally, there is a nonwoven fabric of fibers by a melt-blowing method of polypropylene having an average fiber diameter of 3 μ or more and a microporous resin film.

Problems to be Solved by the Invention However, in the case of the microporous resin film, the thickness thereof is about 1/10 that of the polypropylene fiber non-woven fabric, which is thin compared to the polypropylene fiber non-woven fabric. Although it can be expected to be effective, it was costly as a material for the battery industry, which is based on economies of scale. Further, since the thickness is as thin as several tens of microns and the mechanical strength is weak, it is necessary to pay sufficient attention not to cause damage during the work of wrapping the electrode, and it is extremely difficult to use in manufacturing.

On the other hand, polypropylene fiber non-woven fabric is cheaper in cost, but the pore size generated between fibers is larger than that of the microporous resin film, so the pores are completely melted by the heat generated when the battery is heated. Requires a temperature of 150 ° C. or higher, and keeping the battery at such a high temperature is extremely dangerous from the viewpoint of safety, particularly for an organic electrolyte battery using an organic solvent having a low boiling point. In order to suppress this, it is conceivable to increase the basis weight of the polypropylene fiber non-woven fabric and reduce the pore size generated between the fibers, but in this case, the separator becomes thicker and the specific resistance of the separator itself is high. Then, there is a problem that the discharge performance of the battery is deteriorated.

The present invention is intended to solve the above problems and to reduce the melting temperature when closing the fine pores of the separator without lowering the characteristics of the battery, and to improve the safety of the battery. is there.

Means for Solving the Problems In order to solve the above problems, the present invention provides a separator made of a nonwoven fabric made of fibers of polypropylene resin containing an α-olefin component other than propylene.

Here, the polypropylene-based resin containing an α-olefin component other than propylene means a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-hexene-1 copolymer, a propylene-ethylene-butene-polymer. Examples thereof include a propyne-α-olefin 1 copolymer such as 1 copolymer or a polymer composition comprising a mixture of polypropylene and polyethylene. Among these, it is preferable to use a propylene-ethylene copolymer and a mixed composition of polypropylene and polyethylene from the viewpoint of easy availability as a raw material and cost.

When ethylene is used as the α-olefin component,
The ethylene content is preferably 1 to 5% by weight.

If the ethylene content in the copolymer is less than 1% by weight, the effect of lowering the melting temperature of the non-woven fabric is poor, and if it exceeds 5% by weight, the melting point of the non-woven fabric becomes too low and the separator surface is formed due to an early filming phenomenon. A crack is generated in the crack, and a current again flows from the crack portion to form a short circuit in the battery, which is not preferable. Further, the fibers constituting the non-woven fabric can be made to have an average fiber diameter of 1.5 μm or less, so that the pore size of the non-woven fabric can be made small, and the pores generated between the fibers can be easily closed by the heat at the time of heat generation. .

Action With such a separator, the temperature at which the pores formed between the fibers are closed can be suppressed to 130 ° C. or lower, and the safety of the battery can be improved. Also, the average fiber diameter is 3 μm
From the above, the area occupied by the pores in the separator is almost the same by setting the thickness to 1.5 μm or less, but the pore diameter can be made smaller, the basis weight can be reduced as compared with the conventional polypropylene fiber nonwoven fabric, and the battery characteristics can be improved. It has become possible to improve.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples. In FIG. 1, a power generating element is a separator made of a non-woven fabric, in which a positive electrode mixture (1) and a negative electrode (2) each formed in a strip shape are composed of propylene-ethylene copolymer resin fibers, which is a feature of the present invention ( 3) is inserted between each other, and the whole is wound and formed in a spiral shape. This power generating element has a disc-shaped insulating plate (5) having a hole in the center in a battery case (4), which is vertically arranged. It is arranged and stored. Then, a nonaqueous electrolytic solution, for example, an electrolytic solution in which an inorganic electrolyte is dissolved in a solvent such as dioxolane, dimethoxyethane, or γ-butyrolactone is injected into the battery case (4), and a synthetic resin sealing plate (6) is used.
The opening of the battery case (4) is sealed. The resin sealing plate (6) has a rivet terminal (7) made of corrosion-resistant metal press-fitted and fixed in a hole provided in the central portion thereof, and a positive electrode current collector (8) is electrically attached to the inner surface thereof. It is connected. Therefore, the rivet terminal (7) also serves as the positive terminal. The negative electrode (2) made of metallic lithium has a current collector (9) crimped onto the surface of the lithium, and the lead portion of the current collector is electrically connected to the inner bottom surface of the battery case (4). The case (4) also serves as the negative electrode terminal. Next, the details of the separator of the present invention, the results of comparative examination of the amount of ethylene added, the battery characteristics, and the safety at the time of short circuit are shown.

The battery used in the experiment was 17.5 mm in diameter and 33.5 m in height.
A cylindrical lithium battery with m and an electric capacity of 1200 mAh was used. As the constitution of the lithium battery, a positive electrode active material containing fluorocarbon, and an electrolyte containing 1 mol / l of lithium borofluoride dissolved in a mixed solvent of γ-butyrolactone and dimethoxyethane were used.

The following table shows the fiber contents of the separators of types A to K, the α-olefin content other than propylene, the average fiber diameter of the fibers constituting the nonwoven fabric, the battery surface temperature at the time of a short circuit, and the battery content ejection ratio due to the short circuit ( Each 1000 pieces) is shown.

As is clear from the results in the table, the melting points of the propylene homopolymers indicated by A and H are 160 ° C., whereas the random copolymers of propylene and ethylene, for example, those having an ethylene content of 3.6 wt% are 140 ° C. It is as low as ℃, and the melting point changes depending on the ethylene content, but it is still lower than that of the propylene homopolymer.

Further, although the non-woven fabric composed of the mixed composition of polypropylene and polyethylene of I and J has a substantial micropore blocking temperature slightly higher (5 to 6 ° C.) than the propylene-ethylene copolymer, the propylene homopolymer is nonetheless. It has a lower melting point than that of resin.

In addition to the above, butene-1 is used as an α-olefin,
When a non-woven fabric made of a copolymer resin with propylene was also examined, almost the same results were obtained.

FIG. 2 shows a lithium battery equipped with each of A to K separators.
The discharge characteristics when discharged with a load resistance of 60Ω at 20 ° C are shown.

Fig. 3 shows that each of the above batteries was stored at a high temperature of 85 ° C for 7 days.
The following shows the discharge characteristics when discharged with a load resistance of 60Ω. As is clear from both figures, the batteries using the A to G and I to K separators are superior in voltage characteristics and storage characteristics to the batteries using the conventional H separator.

The non-woven fabrics except H in the table were melt-spun of a melt composition composed of a propylene homopolymer, a propylene-ethylene random copolymer, a propylene-butene-1 copolymer and a mixture of polypropylene and polyethylene. Is blown as fine fibers by a high-speed gas onto a collection plate to produce a non-woven fabric, the so-called melt-blowing method produces an average fiber of 1.5 μ, basis weight of 20 g / m ² , and thickness of 60.
This is a non-woven fabric of μm.

In the battery using the separator A having no ethylene content in which only the average fiber diameter of the conventional product H is changed to 1.5 μm, the battery surface temperature is lowered, but the battery content ejection ratio is
The ratio was 1.0%, which was better than the conventional product H, but showed a bad tendency as compared with the product using the separator made of the nonwoven fabric of the polypropylene resin fiber containing ethylene of the present invention. Fibers made of ethylene-containing polypropylene resin also have B, F, and B when the ethylene content is 0.5 wt%, 5.5 wt%, and 6. wt%.
In G, the contents were gushed out, which was not preferable from the viewpoint of battery safety.

From the results in the table and figure, the preferable content of ethylene is 1.0
~ 5.0 wt%.

Also, even if the average fiber diameter of the fibers forming the nonwoven fabric was 1.0 μm, the same result as 1.5 μm was obtained.

Effects of the Invention As described above, the separator according to the present invention, that is, 1 to 5 wt% of the α-olefin component other than propylene such as ethylene.
The non-woven fabric composed of the polypropylene resin fiber contained in 10% is excellent in battery safety, discharge characteristics and the like.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an organic electrolyte battery according to an embodiment of the present invention, FIG. 2 is a diagram showing discharge characteristics of a battery including various separators before storage, and FIG. 3 is various types when stored at 85 ° C. It is a figure which shows the discharge characteristic of the battery provided with the separator. 1 ... Positive electrode mixture, 2 ... Negative electrode, 3 ... Separator, 4 ...
… Battery case, 5… Insulation plate, 6… Resin sealing plate, 7…
… Rivet terminals, 8,9 …… Current collectors.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toyoji Sugimoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor, Makoto Suzuki 1-15-15, Tanaka, Isogo-ku, Yokohama

Claims (3)

[Claims] 1. A positive electrode using fluorocarbon, manganese dioxide or another metal oxide as an active material, a negative electrode using an active light metal such as lithium as an active material, a separator interposed between the positive and negative electrodes, and an organic electrolyte. Wherein the separator is made of a polypropylene resin containing an α-olefin component other than propylene, and is made of a nonwoven fabric of fibers having an average fiber diameter of 1.5 μm or less. 2. The organic electrolyte battery according to claim 1, wherein the α-olefin component other than propylene is ethylene. 3. The organic electrolyte battery according to claim 1 or 2, wherein the content of ethylene as an α-olefin component is 1 to 5% by weight.