JPH0746611B2 - Thin lithium battery manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present 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 a peripheral portion of a positive / negative bipolar current collector plate is fusion-sealed with a heat-fusible material.

[Conventional technology]

Conventionally used button-type or coin-type lithium batteries generally have a positive electrode in which an active material such as TiS ₂ is mixed with a binder such as Teflon powder and, if necessary, an electron conduction aid such as carbon powder. And lithium or lithium alloy is used as the negative electrode, and a separator is interposed between the both electrodes to dispose between the positive electrode current collector plate and the negative electrode current collector plate, and a lithium salt is used. It has a structure in which an electrolyte, which is a highly fluid liquid composed of a non-aqueous solvent and a non-aqueous solvent, is injected so as to infiltrate into the separator and the positive electrode, and then the periphery of both electrode current collector plates is bent and sealed by sandwiching a packing material. (Reference is unknown).

However, as electronic devices have become smaller, lighter, and thinner in recent years, very thin and high-performance lithium batteries such as card type and flexible type with a total thickness of about 0.5 mm are required. Has been done. In such a thin battery, the battery elements themselves such as the positive and negative electrodes and the separator also need to be thin, and the bonding method is obliged to be adopted for the sealing portion due to restrictions on the processing technology (literature unknown).

[Problems to be solved by the invention]

However, when using a molded body of a mixture of the above-mentioned positive electrode active material, a binder and, if necessary, an electron conduction aid as the positive electrode, it is difficult to mold a constant thin product suitable for a thin battery itself. Moreover, when the thickness is about 0.1 mm, there is a problem that the uniformity such as composition and density and the strength become insufficient. In addition, when adding an electrolyte consisting of a conventional high-fluidity liquid to the battery by dripping, the electrolyte is easy to flow out to the peripheral side because the bipolar current collector plate is also a flat plate for thin batteries, and the required amount is It is very difficult to add it well.

On the other hand, as described above, when adhesive sealing is performed in the peripheral portion of the positive and negative electrode current collector plates, if a coating solution type adhesive is used, the sealing portion width is extremely narrow and flat, so the entire peripheral portion is covered. It is difficult to apply an appropriate amount evenly, and the adhesive before curing may flow into the battery and mix with the electrolyte to adversely affect the battery performance. Further, when the sealing is performed by heat fusion with a heat fusion material such as a hot melt adhesive, it is possible to use an annular sheet having a predetermined width and thickness as the material. Although the drawbacks are solved, there is a problem that the vapor pressure of the liquid electrolyte is increased by heating during fusion and the liquid is scattered to make the sealing itself difficult.

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

[Means for solving problems]

As a result of extensive studies conducted by the present inventors for the above purpose, a viscous electrolyte is used as the electrolyte, and a viscous kneaded material mainly composed of this electrolyte and the positive electrode active material is used as the positive electrode material, whereby the electrolyte is It can be easily added to the battery by the coating means, and it is possible to prevent the liquid electrolyte from flowing out to the peripheral part, and even when the sealing method by heat fusion of the heat fusible material is adopted, it can be heated. Electrolyte does not scatter and can be surely sealed easily, and the positive electrode can be thinly and evenly formed by application means such as screen printing, and its thickness can be arbitrarily adjusted, and the composition and density are uniform. The inventors have found that the following can be obtained, and have reached the present invention.

That is, according to 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 both electrodes is disposed between the positive electrode current collector plate and the negative electrode current collector plate, and In a thin lithium battery having a structure in which a peripheral portion is fusion-sealed with a heat-fusible material, a viscous body containing a lithium salt, a non-aqueous solvent, and a gelling agent is used as an electrolyte, and the positive electrode current collector plate is used. The present invention relates to a method for manufacturing a thin lithium battery, characterized in that a positive electrode comprising a viscous kneaded material layer mainly composed of the electrolyte and the positive electrode active material is applied and formed thereon.

[Constitution / Operation of Invention]

The electrolyte used in the present invention is composed of a lithium salt, a non-aqueous solvent, and a gelling agent as described above,
The thickening effect of the gelling agent makes it a viscous material that does not exhibit high fluidity like conventional liquid electrolytes, so it can be applied to battery elements such as separators and added to the battery, and heat fusion It has an excellent feature that it does not scatter even if it is heated at the time of sealing.

As the lithium salt and the non-aqueous solvent used for such an electrolyte, any of various ones conventionally known for lithium batteries can be used. For example, typical examples of suitable lithium salts include LiBφ ₄ (φ means a phenyl group), LiPF ₆ , LiCF ₃ SO ₃ , LiAsF _{6, and the} like. These may be used in combination of two or more. Alternatively, it may be an adduct of a non-aqueous solvent in advance. On the other hand, typical examples of the non-aqueous solvent include propylene carbonate, γ-butyrolactone, dimethoxyethane, dioxolane and the like, and these may be used in combination of two or more kinds. The concentration of lithium salt is 0.3-3 mol /
l is preferred.

Any gelling agent may be used as long as it has a property of not reacting with a lithium salt and being uniformly mixed with a non-aqueous solvent to form a gel, and a preferable representative example thereof is polymethacrylic acid alkyl ester, and particularly preferable constitution. R represented by the general formula CH ₂ = C (CH ₃ ) COOR of methacrylic acid alkyl ester, which is a unit, is composed of a lower alkyl group such as methyl group, ethyl group and propyl group, and has an average molecular weight of about 5,000 to 20,0000. There are things. The amount of the gelling agent used may be appropriately set so that the viscosity of the viscous material falls within an appropriate range,
If the viscosity is too high, the viscosity will be too high, making it difficult to apply, and if it is too low, the fluidity will be too great and the same problems as in the conventional liquid electrolyte will occur. When using polymethacrylic acid alkyl ester as a gelling agent, the amount used is 10 parts with respect to 100 parts by weight of the non-aqueous solvent.
Approximately 30 parts by weight is a guideline for usage.

As the electrolyte viscous material used in the present invention, there are many suitable combinations of the above-mentioned lithium salt, polymethacrylic acid alkyl ester and non-aqueous solvent, but LiBφ _{4 in} terms of battery characteristics and homogeneity of the electrolyte. The best results have been obtained with a combination of the dimethoxyethane adduct of 1. with polymethylmethacrylate and propylene carbonate.

A feature of the present invention is that the viscous body is used as an electrolyte and that the positive electrode is composed of a viscous kneaded material layer mainly composed of an electrolyte having this viscosity and a positive electrode active material. That is, since such a viscous kneaded material can be applied on the positive electrode current collector by various application means including screen printing, it can be used as a positive electrode for a thin battery, for example, 0.1 mm.
It is easy to form a uniform layer thickness of a degree or less, and it is possible to adjust the thickness, and since it is a kneaded product, there are advantages that the composition and the component density can be made uniform.

Here, as the positive electrode active material used for the positive electrode, it is possible to use various materials conventionally used in lithium batteries, for example, TiS ₂ , MoS ₂ , MoS ₃ , as suitable ones.
_{FeS 2, ZrS 2, NbS 2} , NiPS 3, VSe 2, V 6 O 13, etc. V ₂ O ₅ and the like, which may be used in combination of two or more thereof.

A viscous kneaded material for forming a positive electrode can be obtained by kneading such a positive electrode active material with the electrolyte, but the active material particles in the positive electrode maintain the mutual contact state and reach the surface of the positive electrode current collector plate from the separator side. Since it is necessary to form an electric path, it is desirable that the active material is present in a certain ratio or more. On the other hand, when the filling amount of the active material particles in the positive electrode is too large, the electrolyte for maintaining lithium conductivity in the gaps between these particles becomes small, and the lithium ions are less likely to diffuse and the contribution rate to the reaction decreases. . Therefore, from the above viewpoint, the volume ratio of the positive electrode active material / electrolyte is preferably about 1 / 0.3 to 1/1, particularly preferably 1 / 0.4 to 1 / 0.8.

In the present invention, an electron conduction aid such as carbonyl nickel or acetylene black may be contained in the positive electrode made of a viscous kneaded material for the purpose of improving electron conductivity. The addition amount of such an electron conduction aid may be changed according to the difference in electron conductivity depending on the type of the positive electrode active material used, but normally, it is added in an amount of 5 to 12% by volume in the viscous kneaded material. It is desirable to set the amount. When the electron conduction aid is added as described above, the electric path is easily formed in the positive electrode, so that the use ratio of the positive electrode active material can be lowered to some extent from the above range.

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

FIG. 1 shows an example of the lithium battery according to the present invention. In the figure, 1 is a square plate-shaped positive electrode current collector plate made of stainless steel, 2 is a shallow rectangular dish-shaped negative electrode current collector plate made of stainless steel in which the peripheral portion 2a is bent stepwise toward one surface side,
3 is a heat-fusible material such as a hot-melt adhesive in which the peripheral portions 1a and 2a of the bipolar current collector plates 1 and 2 facing each other are heat-sealed, and a hermetically-sealable ceramic material. 4 is a bipolar current collector. Board
A positive electrode arranged on the positive electrode collector plate 1 side in a space 5 formed between 1 and 2, 6 is a negative electrode made of lithium or a lithium alloy loaded on the negative electrode collector plate 2 side in the space 5,
Reference numeral 7 is a separator made of a porous material such as porous polypropylene interposed between the electrodes 4 and 6.

Here, the electrolyte made of the viscous material is usually added to the battery by pre-coating and impregnating the separator 7 before being assembled. At this time, since the electrolyte is a viscous substance, it does not flow out to the surroundings even if the assembly base surface is slightly inclined or vibration is applied, and drops even when the separator 7 is transported from the application position to the installation position. There is no fear of it, and it is possible to adjust the addition amount in a wide range. The positive electrode 4 is formed by applying a viscous kneaded product obtained by kneading the positive electrode active material, the electrolyte and, if necessary, the electron conduction aid on the positive electrode current collector plate 1 by screen printing or the like as described above. It was done.

On the other hand, as the heat-fusible material 3, the shape before heat-sealing is a molded sheet such as a ring which is preset to a width corresponding to the width of the peripheral portions 1a, 2a of the bipolar current collector plates 1, 2. Can be used. That is, for the sealing operation, the molding sheet may be sandwiched between the both peripheral portions 1a and 2a and pressed against each other, and in this state, the both peripheral portions 1a and 2a may be heated to a predetermined temperature. In the heating process, since the electrolyte is a viscous substance, it does not scatter like a conventional liquid, and reliable sealing can be easily achieved.
Further, as described above, since the form before heat fusion is a solid molded product, the handling operation and the assembling operation are very easy, and, as in the case of using a coating solution type adhesive, There is no fear of flowing in and mixing with the electrolyte.

As the heat-fusible material 3, various materials such as a hot-melt adhesive and a ceramic capable of hermetic sealing can be used.

Further, both lithium and lithium alloy can be used as the negative electrode 6, but lithium alone may react with the electrolyte for a long period of time, so alloying with aluminum or the like is desirable.

The bipolar current collector plate in the battery of the present invention is not only one of which has a dish shape as shown in FIG. 1, but both of which have a dish shape, and a spacer made of ceramic or the like is inserted between the peripheral portions. As a result, both may be flat. Needless to say, when this spacer is used, both surfaces thereof and the bipolar current collector plate are heat-sealed and sealed with a heat-fusible material. The thin battery referred to herein means a battery having a total battery thickness of 1.0 mm or less, particularly about 0.3 to 0.7 mm, and the outer shape can be a shape other than a square, such as a circle, depending on the application.

The lithium battery of the present invention configured as described above has the advantages of reducing the thickness of the positive electrode and the battery assembling described above, as well as using the positive electrode as clearly shown in the comparison of the battery characteristics of the examples and the comparative examples. It has an important feature that the rate is improved, the discharge capacity is large as a primary battery, and the discharge capacity per discharge is large even if charging and discharging are repeated many times. Although the reason for this is not clear, in the positive electrode active material, contact between particles generally weakens due to volume change due to charge / discharge, and in the positive electrode composed of a conventional molded sheet, the active material is penetrated into the non-aqueous solvent. It is presumed that, while the particles are dispersed and the deterioration of the positive electrode is increased, the viscosity of the gel component in the positive electrode prevents movement of the active material particles and suppresses the deterioration of the positive electrode in the present invention. It It should be noted that such an effect is more remarkably exhibited by increasing the electron conductivity by including an electron conduction aid in the positive electrode.

〔The invention's effect〕

The thin lithium battery according to the present invention is formed by using a viscous material containing a gelling agent as an electrolyte, and applying a viscous kneaded material mainly composed of the electrolyte and the positive electrode active material to the positive electrode on the positive electrode current collector plate. As a result, the electrolyte does not scatter when heat-sealing in the periphery of the positive and negative electrode current collector plates, and reliable sealing is possible, and by simple means such as applying the electrolyte. It can be added uniformly to the entire required area without flowing out to the peripheral side, the addition amount can be adjusted over a wide range, and it is possible to easily obtain a positive electrode with a uniform composition and density and a thin and uniform thickness. It has an excellent effect that the positive electrode utilization rate is high without the above problem.

〔Example〕

Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples. In the following, "parts" means "parts by weight".

Dimethoxyethane adduct of Example 1 LiBφ ₄ (LiBφ _4; molar ratio of dimethoxyethane 1: 3) Propylene carbonate 4 22.4 parts
Dissolve in 7.6 parts, add 10.5 parts of polymethylmethacrylate (average molecular weight 12,000) to this, mix and seal, 120 ° C
It was left for 30 minutes to obtain an electrolyte composed of a uniform viscous material.
This electrolyte has an ionic conductivity of 1.8 × 10 ^-3 S / cm at 25 ° C.
It was.

Next, T produced by this electrolyte and CVD (Chemical Vapor Deposition) method
The viscous kneaded product obtained by sufficiently kneading the iS ₂ powder with a mortar at a volume ratio of 30:70 was applied by a screen printing method to a positive electrode current collector plate made of a stainless steel flat plate with a side of 15 mm and a thickness of 0.05 mm. A positive electrode having a square shape of 10 mm on each side and a thickness of 0.1 mm was formed. A 25 μm thick separator made of porous polypropylene (polyplastics brand name JYURAGARD 2400 manufactured by Polyplastics Co., Ltd.) was formed on the positive electrode to have an uneven shape, and the electrolyte was pre-applied in advance to uniformly impregnate the entire thickness. About 0.1m
A m separator was stacked, and a negative electrode made of a lithium-aluminum alloy rectangular plate having a side length of 4 mm and a thickness of 100 μm was stacked on the separator.

Next, a modified polyolefin hot melt adhesive consisting of a square annular sheet with a thickness of 0.05 mm and a width of 2 mm was placed on the periphery of the positive electrode current collector plate, and a square with a side of 15 mm and a thickness of 15 mm.
A negative electrode current collector made of a 0.05 mm plate stainless steel plate was capped, and the peripheral portions of both electrodes were heated to 180 ° C under pressure and heat-sealed to obtain the structure shown in Fig. 1. A thin lithium battery was produced.

Example 2 As a viscous kneaded material for forming a positive electrode, the same electrolyte as in Example 1 and TiS ₂ powder and carbonyl nickel powder were used in a volume ratio of 3
Example 1 except that a kneaded mixture of 0: 65: 5 was used.
A thin lithium battery having the structure shown in FIG. 1 was prepared in the same manner as in.

Comparative Example TiS ₂ powder and Teflon powder produced by the CVD method were mixed in a weight ratio of 10
The mixture of 0: 5 was molded into a sheet having a thickness of 0.1 mm, and this was cut into a square having a side of 10 mm to obtain a positive electrode. This positive electrode was placed on the same positive electrode current collector plate as in Example 1, and an electrolyte made of a viscous material similar to that in Example 1 was dropped on the upper surface of the positive electrode current collector plate, and then a separator not coated with the electrolytic solution (Example 1 The same as the above) was placed, the above electrolyte was applied to the upper surface thereof, and a thin lithium battery was manufactured in the same manner as in Example 1 below.

The thin lithium batteries obtained in the above Examples and Comparative Examples were examined for charge / discharge cycle characteristics under the conditions of a temperature of 25 ° C., a discharge end voltage of 1.5 V, a charge end voltage of 2.7 V, a discharge current of 30 μA, and a charge current of 30 μA. The results shown in FIG. 2 were obtained. The curve in the figure plots the discharge capacity against the number of cycles. The curve A1 in the figure corresponds to Example 1, A2 corresponds to Example 2, and B corresponds to the comparative example.

As is clear from the results shown in FIG. 2, even when the same viscous material is used as the electrolyte, the battery in which the positive electrode is composed of the viscous kneaded material layer containing the electrolyte (Examples 1 and 2) has a conventional molded sheet. The discharge capacity of the primary battery (corresponding to a cycle number of 1) is larger than that of the battery using the positive electrode made of, and the discharge capacity per discharge is remarkably large even when the battery is repeatedly charged and discharged many times. It turns out to be big. Further, it is understood that the battery containing the electron conduction aid in the positive electrode composed of the viscous kneaded material layer (Example 2) has higher performance as a primary battery and a secondary battery than the battery not containing this (Example 1).

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a main part of an embodiment of a thin lithium battery according to the present invention, and FIG. 2 is charge / discharge cycle characteristics of the batteries obtained in the embodiment of the present invention and a comparative example. 1 ... Positive electrode current collector plate, 1a ... Peripheral part, 2 ... Negative electrode current collector plate,
2a ... peripheral part, 3 ... heat-fusible material, 4 ... positive electrode, 6 ...
… Negative electrode, 7 …… Separator

Claims (4)

[Claims] 1. A battery element including a positive electrode, a negative electrode made of lithium or a lithium alloy, and a separator interposed between both electrodes is arranged between the positive electrode current collector plate and the negative electrode current collector plate, and the periphery of the bipolar electrode current collector plate. In a thin lithium battery having a structure fusion-sealed with a heat-fusible material, a viscous body containing a lithium salt, a non-aqueous solvent and a gelling agent is used as an electrolyte, and on the positive electrode current collector plate. A method for manufacturing a thin lithium battery, characterized in that a positive electrode comprising a viscous kneaded material layer mainly containing the above-mentioned electrolyte and a positive electrode active material is applied and formed. 2. The method for producing a thin lithium battery according to claim 1, wherein the viscous kneaded material layer of the positive electrode contains an electron conduction aid. 3. The method for producing a thin lithium battery according to claim 1, wherein the gelling agent is a polymethacrylic acid alkyl ester. 4. The thin lithium according to claim 3, wherein the electrolyte is a viscous body containing a dimethoxyethane adduct of LiBφ ₄ (φ means a phenyl group), propylene carbonate and polymethylmethacrylate. Battery manufacturing method.