JPS61214364A - Thin lithium battery - Google Patents

Abstract

PURPOSE:To make assembly easy and increase performance by using a separator having specified surface structure, and using a viscous electrolyte formed by adding a gelling agent. CONSTITUTION:A viscous solution containing a lithium salt, a nonaqueous solvent, and a gelling agent is used as an electrolyte 9. A microporous propylene film having a lot of recessed and projecting parts on its both sides is used as a separator 8. Since a sufficient volume of electrolyte 9 is retained in the recessed parts, the interface between the separator 8 and a positive electrode 5 and that between the separator 8 and a negative electrode 7 are prevented from the lack of electrolyte, and battery performance is improved. In the battery assembly, the viscous electrolyte 9 does not flow out to the periphery 2a, and the desirable amount of electrolyte can easily be obtained by coating. Furthermore, when the battery is sealed by hot-melt-bonding, the electrolyte does not splash out. Therefore, reliable sealing is obtained.

Description

[Detailed description of the invention] [Industrial application field] This invention uses lithium or a lithium alloy as a negative electrode,
The present invention relates to a thin lithium battery having a structure in which the peripheral portions of positive and negative current collector plates are fused and sealed with a heat-fusible material.

[Conventional technology]

Button-type and coin-type lithium batteries generally have a separator made of a laminated layer of a porous synthetic resin film and a synthetic fiber nonwoven fabric interposed between a positive electrode containing a positive active material and a binder and a negative electrode made of lithium or a lithium alloy. This separator absorbs and holds an electrolyte made of a highly fluid liquid containing lithium salt dissolved in a non-aqueous solvent, and the periphery of the positive and negative current collector plates containing these battery elements is bent and sealed with a backing material in between. (Reference unknown)
.

However, as electronic devices have become smaller, lighter, and more precise in recent years, extremely thin and high-performance lithium batteries such as card-type and flexible types with a total thickness of about 0.5 fl have become available. It is requested.

In such a thin battery, there is a limit to how thin it can be made with the above-mentioned button-type or coin-type structure, so a separator with a diameter of 0.02 to 0.4μ that penetrates the front and back surfaces of a microporous polypropylene film, etc. is used as a separator. It is necessary to use a microporous synthetic resin film with a thickness of approximately 25 μm and having as many micropores as possible, and to adhesively seal the peripheral portions of the positive and negative current collector plates (unspecified literature).

[Problems to be Solved by the Invention] However, in the above-mentioned thin battery, the separator is very thin and has a small amount of voids, and cannot hold a sufficient amount of liquid electrolyte. If this method is adopted, there is a problem in that electrolyte is insufficient at the interface between the separator and the positive and negative electrodes, making it impossible to obtain good battery performance. Therefore, conventionally, the entire internal battery element is immersed in the liquid electrolyte, but when the liquid electrolyte is added dropwise to achieve the above-mentioned immersion state during battery assembly, the bipolar current collector plates for thin batteries are almost completely immersed. Because of the flat plate shape, the electrolyte tends to flow out to the periphery, making it extremely difficult to add the required amount.

On the other hand, when adhesively sealing the periphery of the positive and negative current collector plates as described above, if a paint solution type adhesive is used, the width of the sealing part is very narrow and flat, so the entire periphery can be sealed. It is difficult to apply the appropriate amount evenly, and there is a risk that uncured adhesive may flow into the battery and mix with the electrolyte, adversely affecting battery performance. In addition, when sealing is performed by heat fusion using a heat-fusible material such as a hot-melt adhesive, an annular sheet with an appropriate width and thickness can be used as the material, so the above-mentioned paint solution type However, there was a problem in that the vapor pressure of the liquid electrolyte increased due to heating during fusion, causing the liquid to scatter and making sealing itself difficult.

Therefore, an object of the present invention is to provide a thin lithium battery that is easy to assemble and has excellent performance by solving the above-mentioned problems.

[Means for solving problems]

As a result of extensive studies for the above purpose, the inventors found that by using a separator with a specific surface structure and an electrolyte made viscous with a gelling agent, the electrolyte can be coated. The electrolyte can be added into the battery by some means, and can prevent it from flowing out to the surrounding areas like conventional liquid electrolytes.1. However, it is possible to hold a sufficient amount of electrolyte at the interface between the separator and the positive and negative electrodes, and even if a sealing method using thermally adhesive material is used, the electrolyte will not scatter during heating. The present inventors have discovered that it is possible to easily perform reliable sealing without having to do so, and have come up with the present invention.

That is, in the present invention, a battery element including a positive electrode, a negative electrode made of lithium or a lithium alloy, and a separator interposed between the two electrodes is arranged between a positive electrode current collector plate and a negative electrode current collector plate, and In a thin lithium battery having a structure in which the peripheral portion is fused and sealed with a heat-fusible material, the separator is a microporous polypropylene filler having a large number of irregularities on the front and back surfaces.

The present invention relates to a thin lithium battery characterized in that an electrolyte made of a viscous body containing a lithium salt, a nonaqueous solvent, and a gelling agent is held in the recesses of the separator.

[Structure and operation of the invention]

As mentioned above, the electrolyte used in this invention is composed of a lithium salt, a non-aqueous solvent, and a gelling agent. Since it is a viscous material that does not exhibit fluidity, it can be applied to battery elements such as separators and added into the battery, and it also has the excellent feature of not scattering even when heated during sealing by heat fusion. There is.

As the lithium salt and non-aqueous solvent used in such an electrolyte, any of the various ones conventionally known for use in lithium batteries can be used. For example, representative examples of suitable lithium salts include LiBφ4 (φ means a phenyl group), LiPF6, LicF, SO8,
[, 1AsFa, etc., and these may be used in combination of two or more types, or may be made into an adduct of a non-aqueous solvent in advance. On the other hand, suitable typical examples of the non-aqueous solvent include propylene carbonate, T-butyrolactone, dimethoxyethane, dioxolane, etc., and two or more of these may be used in combination. The concentration of lithium salt is 0.3 to 3 m0I! /l! is preferred.

The gelling agent may be any material as long as it does not react with lithium salts and has the property of uniformly mixing with non-aqueous solvents to form a gel, and representative examples include polymethacrylic acid alkyl esters, and particularly preferred compositions The general formula of the unit methacrylic acid alkyl ester is CH2=C(CH
3) R represented by C0OR consists of a lower alkyl group such as a methyl group, an ethyl group, or a propyl group, and the average molecular weight is s
, ooo to about 20,000. The amount of gelling agent to be used should be set so that the viscosity of the viscous material is within an appropriate range (in this case, if the viscosity is too high, the viscosity will be too high and it will be difficult to apply. If it becomes too low, the fluidity will be too high, causing the same problems as with conventional liquid electrolytes.Incidentally, when polymethacrylic acid alkyl ester is used as a gelling agent, the amount used is 100 parts by weight of the non-aqueous solvent. On the other hand, the amount to be used is approximately 10 to 30 parts by weight.

The feature of this invention is to use the above-mentioned viscous body as an electrolyte, and to use a microporous polypropylene film having many irregularities on the front and back surfaces as a separator. In other words, since the electrolyte is a viscous substance, it can be added to the inside of the battery by applying it to the front and back surfaces of the separator or the sides of the positive and negative electrodes opposite the separator. The amount of electrolyte that can be retained is small, and when a normal flat separator is pressed against the positive and negative electrodes during battery sealing, most of the applied electrolyte moves to the side, causing the difference between the positive and negative electrodes and the separator. Electrolyte becomes insufficient at the interface, leading to a decline in battery performance. However, in a separator that has many irregularities on the front and back surfaces, the electrolyte is retained in the recesses, so that a sufficient amount of electrolyte can be present in the separator part, especially at the interface with the positive and negative electrodes, and High performance can be achieved in any secondary battery.Means for forming a large number of irregularities on the front and back surfaces of a separator made of such a microporous polypropylene film include:
The original sheet of the film described above is passed between partially heated rolls having an uneven surface, or the original sheet or the separator after cutting is sandwiched between molds having an uneven surface and partially heated to deform it. However, if a small amount is to be used, the tip of a heated bar may be pressed against the separator many times to form irregularities. As for the size of such irregularities, it is desirable that the depth of the recesses is larger than the thickness of the separator, and in particular, the depth of the recesses is 0.05 to 0.
It is preferable that the amount is about 4tx.

Further, the shape of the recessed portion can be various shapes such as a hemispherical shape, a polygonal shape, a groove shape, and an irregular groove shape.

The material of the separator is polypropylene because it is highly suitable as a separator for thin lithium batteries in terms of solvent resistance, strength, processability, etc., and also because it has excellent porosity in the microporous film that can be manufactured at present. This is because the ratio is small and the effect of applying this invention is large. Moreover, the thickness of such microporous polypropylene film is 25 to 50 μm.
The suitable pore diameter is about 0.02 to 0.4/''.

Next, the battery configuration of the present invention will be explained based on the drawings.

FIG. 1 is a vertical cross-sectional view of the essential parts of a thin lithium battery to which the present invention is applied, and FIG. 2 is an enlarged view of the circle (2) in FIG. 1. In FIG. 1, 1 is a rectangular flat positive electrode current collector plate made of stainless steel, 2 is a rectangular flat negative electrode current collector plate also made of stainless steel, and 3 is a peripheral portion 1a of the bipolar current collector plates 1 and 2. ,
2 a rectangular annular ceramic spacer interposed between
4 is a heat-fusible material made of a hot-melt adhesive or a hermetically sealable ceramic that heat-seals the inner surfaces of the peripheral parts 1a and 2a of the bipolar current collector plates 1 and 2 and the front and back surfaces of the spacer 30; 5 is a positive electrode placed on the positive electrode current collector plate 1 side in the space 6 formed between the two electrode current collector plates 1 and 2, and 7 is a lithium or lithium alloy placed in the space 5 on the negative electrode current collector plate 2 side. The negative electrode 8 is a microporous polypropylene film color separator interposed between the two electrodes 5 and 7 and having many irregularities on the front and back surfaces.

As shown in FIG. 2, the electrolyte 9 made of a viscous material can be applied to both sides of the separator 8 in advance, or applied to the separator surface of the positive and negative electrodes 1°2 or/and the surface of the separator 8, depending on the installation procedure when assembling the battery elements. It is added into the battery by coating, but even if the positive and negative electrodes 1 and 2 and the separator 8 are pressed together during sealing, the recesses 8 on both sides of the separator 8
It is held at a. Note that 8b is a micropore in the separator 8, into which the electrolyte 9 also permeates.

As the heat-fusible material 4, it is possible to use a material whose form before heat-fusion is a formed sheet, such as an annular sheet, whose width is preset to correspond to the width of the peripheral parts 1a and 2a of the bipolar current collector plates 1 and 2. . That is, in the sealing operation, the molded sheet is placed between the bipolar current collector plates 1 and 2.
and the spacer 3, and in this state, the peripheral parts 1a and 2a are heated to a predetermined temperature. In this heating process, since the electrolyte 9 is a viscous substance, it does not scatter unlike conventional liquids, and reliable sealing is easily achieved. Furthermore, as mentioned above, since the form before heat fusion is a solid molded product, it is very easy to handle and assemble. There is no danger that it will flow into the water and mix with electrolytes.

Note that various materials can be used as the heat-fusible material 4, including a hot-melt adhesive and a hermetically sealable ceramic.

Further, as the positive electrode 5, a sheet formed by mixing an active material, a binder such as Teflon powder, and an electron conduction aid such as carbon powder as necessary may be used. A viscous material obtained by kneading a viscous material with an active material and, if necessary, a conductive additive, can be preferably used. That is, since the latter viscous material can be applied and formed on the positive electrode current collector plate 1 by screen printing or the like, the forming process like the former is unnecessary, and the forming operation is extremely simple and cost-effective.
It is excellent in applicability to thin batteries because it can be easily made into thin layers.

As the active material used for the positive electrode 5, various materials conventionally known as positive electrode active materials for lithium batteries can be used, but particularly preferred ones include TiS2, Mo5z,
Examples include VsO13, ■203, VSe2, and N1PSa, and two or more of these may be used in combination.

Furthermore, both lithium and lithium alloys can be used as the negative electrode 7, but since lithium alone may react with the electrolyte 9 over a long period of time, it is desirable to alloy it with aluminum or the like.

In the battery configuration shown in FIG. 1, the spacer 3 is inserted in the sealing part, but if one or both of the positive and negative electrode current collector plates 1 and 2 is shaped like a dish with a bent peripheral part, the spacer 3 can be inserted into the sealing part. The space 5 can be secured without intervening, and the bipolar current collector plates 1 and 2 can be directly fused and sealed with the heat-fusible material 3. Furthermore, the term "thin battery" as used herein means that the total thickness of the battery is 1.0 mm or less, particularly 0.3 to 0.0 mm.
It refers to about 7 birds, and the external shape can be round or round depending on the purpose.

In the thin lithium battery of the present invention constructed as described above, a sufficient amount of electrolyte is always present at the interface between the separator and the positive and negative electrodes, and the electrolyte compensates for changes in the shape of the negative electrode surface due to mass transfer during charging and discharging. Thus, no gaps are created, and substantial contact between the positive and negative electrodes and the electrolyte is stably maintained. Therefore, in a primary battery to which the present invention is applied, the discharge utilization rate of the positive and negative electrode active materials is improved, and in a secondary battery, the discharge utilization rate per charging/discharging cycle and charge/discharge cycle characteristics are improved.

[Effects of the Invention] The thin lithium battery according to the present invention uses a viscous material containing a gelling agent as an electrolyte, and uses a microporous polypropylene film with many irregularities on the front and back surfaces as a separator. Although the separator for thin batteries is very thin and has only a small electrolyte retention capacity, it is an excellent battery because a sufficient amount of electrolyte is retained in the recesses and no electrolyte shortage occurs at the interface between the separator and the positive and negative electrodes. Demonstrates excellent battery characteristics. In addition, when assembling and manufacturing the battery of this invention, since the electrolyte is a viscous substance, there is no risk of it flowing out to the surrounding area, unlike conventional electrolytes made of highly fluid liquids. An appropriate amount can be added into the battery, and the electrolyte does not scatter during sealing by heat fusion, allowing reliable sealing.

〔Example〕

Examples of the present invention will be specifically described below in comparison with comparative examples. In addition, in the following, parts mean parts by weight.

Example A metal rod having a hemispherical tip with a radius of 0.3 was heated to 150°C on a microporous polypropylene film (product name: Duraguard 2400, manufactured by Polyplastics Co., Ltd.) with a square shape of 11a+ on one side and a thickness of 25μ. The separator was pressed many times to produce a separator with an uneven structure in which the depth of the hemispherical recesses was approximately 0.3 mm.

On the other hand, LiBφ4 dimethoxyethane adduct (L +
A mixture consisting of 22.4 parts of B11'4.3 parts ME), 47.6 parts of propylene carbonate, and 10.5 parts of polymethyl methacrylate (average molecular weight 12,000) was allowed to stand at 120°C for 30 minutes under a sealed lid. An electrolyte consisting of a homogeneous viscous substance was prepared. This electrolyte had an ionic conductivity of 1.8 x 10 S/am at 25°C.

Next, this electrolyte and TiS2 powder were mixed at a volume ratio of 30 near 0.
The resulting mixture was coated by screen printing on a positive electrode current collector plate consisting of a stainless steel flat plate with a square side of 15w11 and a thickness of 0.05rtm. A 1 mt positive electrode was formed. On top of this positive electrode, the separator having the uneven structure with the electrolyte uniformly applied on both sides is laminated, and on top of this separator, there are 4 pieces of lithium-aluminum alloy with a thickness of 10 mm on each side.
Negative electrodes made of square plates of 0JtIn were laminated.

Next, a modified polyolefin hot-melt adhesive consisting of a rectangular annular sheet with a thickness of 301 inches and a width of 2 mm and a ceramic spacer in the shape of a rectangular ring with a thickness of 0.3 ttttx and a width of 2 mm were placed on the peripheral part of the positive electrode current collector plate. Furthermore, with hot melt adhesive similar to the above placed on this spacer, a negative electrode current collector similar to the positive electrode current collector is covered, and the peripheral parts of both electrode current collector plates are pressed at 180°C. Heat it to seal it by heat fusion,
A thin lithium battery having the structure shown in FIG. 1 and having a total thickness of 0.45 m was manufactured.

Comparative Example A thin lithium battery was produced in the same manner as in the example except that a flat microporous polypropylene film (original film used in the example) having no uneven structure was used as a separator.

As a result, the results shown in Figure 3 were obtained. Also, for the same battery mentioned above, the end of charging was 2°7V and the end of discharging was 1.5V.

When the charge/discharge cycle characteristics were examined using 30 μA discharge and 30 μA charge, the results shown in FIG. 4 were obtained. In both figures, curve A is the characteristic of the battery of the example, and curve B is the characteristic of the battery of the comparative example.

As is clear from the results shown in FIGS. 3 and 4, the battery of the present invention using a separator with unevenness has a higher temperature than the battery of the comparative example, which uses a viscous material as an electrolyte but has a flat separator. It has a high discharge utilization rate, and as a secondary battery, there is little decrease in discharge capacity due to repeated charging and discharging (
It can be seen that it has high performance.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view of the main part of an example of a battery according to the present invention, Fig. 2 is an enlarged view of the circle (■) in Fig. 1, and Fig. 3 is a battery obtained in an example of the present invention and a comparative example. Fig. 4 is a constant current discharge characteristic diagram of the same battery. DESCRIPTION OF SYMBOLS 1... Positive electrode current collector plate, 1a... Peripheral part, 2... Negative electrode current collector plate, 2a... Peripheral part, 4... Heat-fusible material, 5
...Positive electrode, 7...Negative electrode, 8...Separator, 8a
...concavity, 8b...micropore, 9...electrolyte patent applicant Hitachi Maxell Co., Ltd. Fig. 2 9; electric) V through Fig. 3 11 (mA→

Claims (1)

[Claims] (1) A battery element including a positive electrode, a negative electrode made of lithium or a lithium alloy, and a separator interposed between the two electrodes is arranged between a positive electrode current collector plate and a negative electrode current collector plate, and a battery element including a positive electrode, a negative electrode made of lithium or a lithium alloy, and a separator interposed between the two electrodes is arranged, and In a thin lithium battery that is fused and sealed with a heat-fusible material, the separator is made of a microporous polypropylene film that has many irregularities on the front and back surfaces, and lithium salt and a non-aqueous solvent are placed in the concave parts of the separator. A thin lithium battery characterized by retaining an electrolyte made of a viscous material containing a gelling agent and a gelling agent.