JPS6220263A - Thin type lithium battery - Google Patents

Abstract

PURPOSE:To increase leakage resistance of a thin type lithium battery by using a viscous electrolyte comprising lithium salt, lithium polymethacrylate, and nonaqueous solvent in which these materials are dissolved. CONSTITUTION:A positive electrode 4, a separator 7, and a negative electrode 6 comprising lithium are placed between a positive current collecting flat plate 1 made of stainless steel and a cup-shaped negative current collecting plate whose periphery 2a is pressed in a step form, and the peripheries 1a and 2a are sealed with adhesive 3. A viscous electrolyte comprising lithium salt, lithium polymethacrylate, and nonaqueous solvent in which these materials are dissolved. Leakage of electrolyte can be prevented regardless of hot-melt type sealing.

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 positive and negative current collector plates are adhesively sealed at opposing flat peripheral parts.

[Conventional technology]

Conventionally popular button-type and coin-type lithium batteries generally have a separator interposed between a positive electrode containing a positive electrode active material and a binder and a negative electrode made of lithium or a lithium alloy to form a can. The separator and the positive electrode are placed between the positive electrode current collector plate and the negative electrode current collector plate, and the separator and the positive electrode are infiltrated with an electrolytic solution, which is a highly fluid liquid in which a lithium salt as an electrolyte is dissolved in a non-aqueous solvent. It has a structure in which the rising edge of the current collector plate is sealed by sandwiching a backing material and caulking and bending it (unspecified literature).

However, as electronic devices have become smaller, lighter, and thinner in recent years, the lithium batteries used in these devices have become very thin, such as card-type or flexible types, with a total thickness of about 0.5 mm. High performance is required. When it comes to such thin batteries, the sealing means for the button-type or coin-type batteries described above has a total battery thickness of 1.5 mm due to structural and processing technology constraints. Since the limit is approximately 0 mm, it is necessary to adopt a method of sealing the flat opposing peripheral edges of the positive and negative current collector plates with an adhesive (unspecified literature).

[Problems to be Solved by the Invention] However, when the above-mentioned highly fluid electrolyte is used in such a thin battery, since the bipolar current collector plate becomes almost flat due to the thinning, the battery During assembly, the electrolytic solution tends to leak out, making it difficult to secure the required amount, and sealing becomes extremely difficult due to wetting of the periphery of the bipolar current collector plates. In addition, after assembly, thin batteries tend to produce a-liquid because the electrolyte always comes into contact with the narrow sealing part during use, making reliability difficult. Furthermore, when used as a secondary battery, charging and discharging By repeating this process, the negative electrode lithium precipitates in a dendrite shape, which tends to cause short circuits, resulting in a shortened lifespan.

On the other hand, when sealing such a thin battery by heat fusion using a heat-adhesive material such as a hot-melt adhesive, the material is in the form of an annular sheet with an appropriate width and thickness set in advance. Since it can be used, there is an advantage that there is no need for a coating operation as in the case of a general paint solution type adhesive, and there is no fear of it flowing into the inside of the electrode 11!2. However, in this case, conventional electrolytic solutions have a problem in that the vapor pressure increases during heating during fusion, and the liquid scatters, making sealing itself difficult.

Note that special batteries using solid electrolytes have also been proposed, and it is conceivable that solid electrolytes may be used in thin batteries as well, but such solid electrolytes have significantly lower ionic conductivity than the electrolytes described above. There are drawbacks such as poor battery performance due to low battery life, and a complicated manufacturing process that increases costs.

[Means for Solving the Problems] As a result of intensive studies to solve the problems described in item 2, the inventors have developed a solution using a viscous material containing specific components in place of the conventional electrolyte. If the electrolyte is assembled into a battery, there is no risk of it leaking out like with conventional electrolytes, the required amount can be secured, sealing with adhesive can be performed without any problems, and the viscous substance can be added by painting. It is easy to add, and even if a sealing method is used by heat-sealing a heat-fusible material, the viscous material does not scatter, allowing for sufficient sealing, and in addition, leakage is less likely to occur. We discovered that a thin lithium battery that is highly reliable and has a long life even as a secondary battery can be obtained, leading us to create this 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 with a flat periphery adhesive-sealed structure, the battery contains a viscous lithium salt consisting of a lithium salt as an electrolyte, a lithium salt of polymethacrylic acid, and a non-aqueous solvent that dissolves both of them. The present invention relates to a thin lithium battery characterized in that a lithium oxide is added thereto.

[Structure and operation of the invention]

In this invention, the lithium salt of polymethacrylic acid used as a component of the viscous body functions as a gelling agent that causes a gelling action with a non-aqueous solvent,
This gelation increases the viscosity of the entire component including the electrolyte, resulting in a viscous body that can be applied and does not scatter even when heated during sealing by thermal fusion.

Note that the additive that brings about the thickening effect by gelation must have good solubility in non-aqueous solvents and be non-reactive with the lithium salt of the electrolyte. From this point of view, although polymethacrylic acid can be expected to have a gelling effect, it is unsuitable due to its reactivity with lithium salts, whereas the monolithium salt of polymethacrylic acid used in this invention is no longer an electrolyte. There is no risk of reaction with certain lithium salts, and it has good solubility in non-aqueous solvents, as well as excellent stability in batteries.

As such a lithium salt of polymethacrylic acid, it is possible to use either one obtained by polymerizing a lithium methacrylate monomer by an appropriate means or one obtained by reacting polymethacrylic acid with a lithium component.
Particularly suitable are those having an average molecular weight of about 5.000 to 12,000.

The amount of the lithium salt of polymethacrylic acid to be used is preferably in the range of 4 to 40% by weight, most preferably in the range of 10 to 20% by weight of the entire viscous body. If the amount used is too large, the internal resistance of the battery will increase and the viscosity of the viscous material will become too high, making operations such as painting difficult. Conversely, if it is too small, the fluidity of the viscous material will increase. Similar problems arise as with conventional electrolytes.

In this invention, the lithium salt to be mixed into the viscous body as an electrolyte can be any of a variety of substances conventionally known as electrolyte components for lithium batteries; do),
L iBF I L + P Fa, LiCF3SO3, L
Examples include iAsF6, which can also be used in the form of an adduct of a non-aqueous solvent, or two or more types can be used in combination. In addition, Liclo, which is conventionally known as an electrolyte component,
, is undesirable because it is dangerous to handle. Further, the concentration of such a lithium salt is preferably 0.3 to 3 mol/l, particularly preferably 0.5 to 1 mol/l.

As a non-aqueous solvent, one that does not react with the lithium salt as an electrolyte, can dissolve both the lithium salt and the lithium salt of polymethacrylic acid, and has the property of gelling when mixed with the lithium salt of polymethacrylic acid. It can be used in various ways.

Particularly preferred are propylene carbonate, T-butyrolactone, dimethoxyethane, and dioxirane, and two or more of these may be used in combination.

In order to prepare a viscous body containing the above three components, a method of mixing and dissolving a lithium salt and a lithium salt of polymethacrylic acid in a non-aqueous solvent may be adopted, but a particularly suitable method is to use a lithium salt. There is a method in which a reaction product obtained by polymerizing a lithium methacrylate monomer in a nonaqueous solvent in which lithium methacrylate is dissolved is directly used as the viscous body. In other words, in the latter method, the solubility of the lithium methacrylate monomer in non-aqueous solvents is greater than that of the lithium salt of polymethacrylic acid in the former method, so the dissolution operation is easier, and moreover, the viscous material is more uniform in composition. It has the advantage of being easy to obtain.

In addition, as a viscous body containing an electrolyte used in this invention,
There are many suitable combinations of the above-mentioned lithium salt and non-aqueous solvent, but in terms of battery characteristics and homogeneity of the viscous material, there are many suitable combinations.
The best results have been obtained with the combination of iBφ4 dimethoxyethane adduct and propylene carbonate.

FIG. 1 shows an example of a lithium battery according to the present invention. In the figure, ■ is a rectangular flat positive electrode current collector plate made of stainless steel, and 2 is a stainless steel plate whose periphery is bent stepwise toward one side to provide a flat periphery 2a in the same direction as the main surface. 3 is an adhesive layer that seals between the opposing peripheral parts 1a and 2a of the bipolar current collector plates 1 and 2, and 4 is a layer formed between the bipolar current collector plates 1 and 2. a positive electrode arranged on the positive electrode current collector plate 1 side in the space 5; 6 a negative electrode made of lithium or a lithium alloy loaded on the negative electrode current collector plate 2 side in the space 5; 7 interposed between the two electrodes 4 and 6; The separator 8 is made of a porous material such as porous polypropylene, and is a rectangular ring-shaped frame made of polypropylene or the like, which is disposed so as to surround the positive electrode 4 .

In this case, the viscous material containing the electrolyte described above is usually added to the inside of the battery by coating and impregnating the separator 7 in advance before assembly. At this time, the viscous material containing the electrolyte does not flow out to the surrounding area even if the assembly base is slightly inclined or vibration is applied, and the viscous material containing the electrolyte does not drip out even when the separator 7 is transported from the installation position to the installation position. There is no danger, and the amount added can be adjusted over a wide range.

On the other hand, as the adhesive layer 3, a general paint solution type adhesive can also be used, but one made of a heat-fusible material is particularly suitable. As the heat-fusible material 3, a material whose form before heat-fusion is a molded 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 is used. can. In other words, the sealing operation is performed at both peripheral parts 1 and 2.
The above-mentioned molded sheet may be sandwiched and pressed between a and 2a, and in this state, the peripheral portions 1a and 2a may be heated to a predetermined temperature.

In this heating process, as described above, the viscous material does not scatter unlike conventional electrolytes, and reliable sealing is easily achieved. Furthermore, as mentioned above, since the form before heat fusion is a solid molded product, handling and assembly are very easy, and the space 5 can be easily handled and assembled, unlike when using a paint solution type adhesive. There is no risk of it flowing into the tank and mixing with the viscous material.

In addition, such heat-fusible materials 3 include hot melt 1-type adhesives, hermetically sealable ceramics, and others.
Various types can be used.

Further, as the positive electrode 4, a sheet formed by mixing an active material, a binder such as Teflon powder, and, if necessary, an electron conduction aid such as carbonyl nickel may be used. A viscous material obtained by kneading a viscous material containing an electrolyte with an active material and, if necessary, a conductive additive, can be preferably used. In other words, the latter viscous material can be applied and formed on the positive electrode current collector plate 1'' by screen printing, etc., so the forming process like the former is not necessary, and the forming operation is extremely simple and cost-effective, as well as being able to form a thin layer. Because it is easy to make, it has excellent applicability to thin batteries.

The frame 8 has a function of setting the amount of the viscous material to be applied when the viscous material is used as the positive electrode 4. That is, this frame 8 is placed on the positive electrode current collector plate 1 in advance,
Since the coating amount becomes constant by filling the inside of the frame with the viscous substance, the thickness and size of the frame 8, that is, the surrounding area, can be determined according to the desired coating amount.

As the active material used for the positive electrode 4, various materials conventionally known as positive electrode active materials for lithium batteries can be used, but particularly preferred ones include TiS, MoS2,
v60I3, V2O9, VSe2, N i P S 3
These may be used in combination of two or more types.

Furthermore, both lithium and lithium alloys can be used as the negative electrode 6, but since lithium alone may react with the viscous material over a long period of time, it is desirable to alloy it with aluminum or the like.

The lithium battery of the present invention constructed as described above has the above-mentioned advantages in terms of battery assembly by using a specific viscous material in place of the conventional electrolyte, as well as a comparison of battery characteristics between Examples and Comparative Examples described later. As clearly shown in , it has an important characteristic that the life of a secondary battery is dramatically increased compared to those using a normal electrolyte. The reason for this is not clear, but when the battery is disassembled and observed in detail after a certain amount of charging and discharging, it is found that in batteries using a normal electrolyte, lithium reaches from the negative electrode through the separator to the inside of the positive electrode. In contrast, in the battery of the present invention, dendrite-like precipitates are hardly observed. Therefore, in the battery of this invention, the gel component in the viscous material acts to kill the specific active sites on the electrodeposited lithium surface, and as a result, lithium dissolution and precipitation occurs uniformly and smoothly over the entire surface of the negative electrode during charging and discharging, resulting in dendrites. It is presumed that short circuits caused by such precipitates are prevented.

In the battery of the present invention, one of the current collector plates may be dish-shaped as shown in FIG. 1, or both may be dish-shaped, or both may be flat plate-shaped with a ceramic layer between the peripheral parts. It is also possible to have a structure in which a spacer, such as a product made of aluminum or the like, is interposed. When using this spacer, it goes without saying that both surfaces of the spacer and the bipolar current collector plates must be adhesively sealed. In addition, the external shape of the battery may be polygonal or circular other than rectangular.
It can be made into various shapes depending on the purpose. Further, although the total thickness of the battery is not particularly limited, the application effect of the present invention is large when the total thickness of the battery is 10 mm or less, preferably about 0.3 to 0.7 mm thick.

〔Effect of the invention〕

Since the thin lithium battery of the present invention has a specific viscous material containing an electrolyte added to the inside of the battery, the viscous material is not used to flow out when assembling the battery, so it is necessary to apply the required amount by painting, etc. It can be added uniformly to the entire predetermined area within the battery with simple operations, and the amount added can be adjusted over a wide range, allowing for reliable sealing with adhesive.
In addition, since the electrolyte is non-fluid, it can be prevented from coming into contact with the sealing portion, so leakage is less likely to occur, making it highly suitable for use as a thin battery. Furthermore, in this battery, even if a heat-fusible material formed into a sheet shape that is easy to handle and seal is used as the adhesive for sealing, the viscous material will scatter due to the heat during the welding process. It is possible to achieve sufficient sealing without any damage.

Furthermore, since this battery ideally maintains the reversibility of the negative electrode lithium during charging and discharging, it has an extremely long life as a secondary battery.

[Example] Hereinafter, an example of the present invention will be specifically described in comparison with a comparative example. In addition, in the following, parts mean parts by weight.

Example I Dimethoxyethane adduct of LiBφ4 (L i Bφ4
11.2 parts of dimethoxyethane (mole ratio 1:3) was dissolved in 2378 parts of propylene carbonate, and 50 parts of lithium methacrylate monomer was added and dissolved in this solution. Next, 0.05 part of benzoyl peroxide was added as a polymerization initiator to this solution, and this was sealed in a pressure-resistant metal container and held at 110'C for 3 hours to cause a polymerization reaction. After cooling to room temperature, When taken out, a semi-solid viscous material with almost no fluidity was obtained. 25 of this viscous material
The ionic conductivity at °C is approximately 10×10 S/cTn
Met.

Next, this viscous body and TiS powder were mixed in a weight ratio of 50:
Polypropylene 1/5 mm was placed on the surface of a positive electrode current collector plate consisting of a square stainless steel plate with a side of 1.5+++ m and a thickness of 0.0 parts and 5 mm. Apply it to the inside of a rectangular frame made of plastic, and make a square with a side of 10 and a thickness of 100P.
n positive electrodes were formed. On this positive electrode, an uneven shape is formed on a porous polypropylene separator (product name: Duraguard 24.OO, manufactured by Polyplastics) with a thickness of 25) m, and the above-mentioned viscous material is applied in advance to uniformly coat the entire surface. A negative electrode made of a lithium-aluminum alloy and having a thickness of 801'' and made of a square foil having a side of 4 mm was further laminated on this separator.

Next, on the peripheral part of the positive electrode current collector plate, a thickness of 0.05 mm and a width of 2
With the modified polyolefin hot melt adhesive made of a rectangular annular sheet of RNM placed on the
A negative electrode current collector plate made of a dish-shaped stainless steel plate with a square shape and a thickness of 0.05 mm was covered with a negative electrode current collector plate, and the peripheral areas of both electrode current collector plates were heated to 180°C under pressure welding and sealed by heat fusion. A thin lithium battery having the structure shown in FIG. 1 and having a total thickness of 0.5 mm was manufactured.

In this battery manufacturing process, no flow of the viscous material impregnated into the separator to the peripheral area was observed, and a reliable sealing state was achieved without scattering of the viscous material during heat fusion.

Example 2 41.0 parts of LiBF was mixed with 1-12.0 parts of propylene carbonate.
In this solution, 2.05 parts of lithium methacrylate monomer and 0.0 parts of benzoyl peroxide as a polymerization initiator were dissolved in
．． 02 parts were added and dissolved. This solution was then sealed in a pressure-resistant metal container and held at 150°C for 10 hours to allow a polymerization reaction. When taken out after cooling to room temperature, a semi-solid viscous material with almost no fluidity was obtained. Ta. The ionic conductivity of this viscous material at 25°C is approximately 1.
．． It was 0x10 S/6m. Next, using this viscous material, a thin lithium battery having a total battery thickness of 0.5 mm was produced in the same manner as in Example 1.

Example 3 61 parts of LiPF and 2 parts of lithium salt of polymethacrylic acid (average molecular weight 10,000) were added and mixed to 127 parts of propylene carbonate and dissolved, and this was mixed under sealed conditions for 13
The mixture was heated at 0°C for 30 minutes to obtain a uniform semi-solid viscous body. The ionic conductivity of this viscous material at 25°C is approximately 1. , 5X], OS/c1n. Next, using this viscous material, a battery with a total thickness of 0.5
A thin lithium battery with a diameter of 1 mm was fabricated.

Comparative Example A square plate-shaped positive electrode with a side of 10πm and a thickness of 0 and 1 mm was prepared by pressure molding a mixture of TiS powder and Teflon powder in a weight ratio of 100:5, and this was placed on the same positive electrode current collector plate as in Example 1. It was placed on. Next, an electrolytic solution was prepared by dissolving 112 parts of LiBφ4 dimethoxyethane adduct (same as in Example 1) in 23.78 parts of propylene carbonate, and this electrolytic solution was dropped onto the above positive electrode. A separator similar to Example 1 which was not impregnated with an electrolytic solution was laminated, and the electrolytic solution was added onto this separator, and then a negative electrode similar to Example 1 was laminated. Next, with an epoxy adhesive applied to the periphery of the positive electrode current collector plate, a negative electrode current collector plate similar to that in Example J is covered, and the adhesive is cured to seal the battery. A 0.5 mm lithium battery was fabricated.

In this battery manufacturing process, even though the electrolytic solution was very carefully dropped twice, a high rate of defective products occurred due to the electrolytic solution flowing out to the periphery of the battery. Moreover, the operation of applying the epoxy adhesive was not easy.

The thin lithium batteries obtained in the above examples and comparative examples were used as secondary batteries at a temperature of 30μA at 25°C.
The charging/discharging cycle characteristics due to constant current of 2.
Measurement was made with a discharge end voltage of 7V and a discharge end voltage of 1.51. The results are shown in FIG. Note that the curve A1 in the figure corresponds to Example 1, A2
1 corresponds to Example 2, A3 corresponds to Example 3, and B corresponds to Comparative Example.

As is clear from the results shown in Figure 2, batteries using normal electrolytes have a significant drop in discharge capacity due to repeated charging and discharging, and have a short lifespan as secondary batteries. Electrical device 1 according to the present invention using a viscous material of
It can be seen that with one particle, the decrease in discharge capacity due to repeated charging and discharging is extremely small, and the battery has an ideal long life as a secondary battery.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of an example of a thin lithium battery according to the present invention, and FIG. 2 is a chart of charge-discharge cycle characteristics of batteries obtained in Examples and Comparative Examples of the present invention. ■...Positive electrode current collector plate, 1a - Peripheral part, 2 Negative electrode current collector plate,
2a... Peripheral area, 3 Adhesive layer, 4... Positive electrode, 6 Negative electrode, 7 Separator

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 the flat shape of the opposite electrode current collector plates is arranged between the positive electrode current collector plate and the negative electrode current collector plate. In a thin lithium battery with a structure in which the periphery of the battery is adhesively sealed, a viscous material consisting of a lithium salt as an electrolyte, a lithium salt of polymethacrylic acid, and a non-aqueous solvent that dissolves both is added inside the battery. A thin lithium battery characterized by: