JPH02291664A - Manufacture of electrode in sheet form - Google Patents

Abstract

PURPOSE:To facilitate molding a material into a sheet from by making up an electrode in a sheet form which is used for a spiral type lithium battery, from an active material mainly composed of manganese dioxides and a mixing agent composed of poly vinyl butyral as a binder, dibutyl phthalate as a plasticizer and of alcohol as a solvent. CONSTITUTION:A lithium-manganese battery is made up out of a positive electrode 5, a separator 6, a negative electrode 7, a battery can 8, an insulating gasket 9, a connecting plate 10, a sealing plate 11 and lead terminals 12 and 13. In this constitution, the electrode in a sheet form to be used as the positive electrode 5 is formed in the following way. Namely, poly vinyl butyral, dibutyl phthalate and alcohol are added to an active material mainly composed of manganese dioxides. After the mixture of them is kneaded, it can be extruded and heat-treated while being heated stepwise up to temperature less than 300 deg.C so as to be pressed with pressure thereafter so that it is thereby transformed into the electrode in a sheet form with specified thickness and density provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a sheet-like electrode used as a positive electrode of a spiral-shaped lithium battery or the like.

Conventional technology> In non-aqueous electrolyte batteries, such as lithium manganese batteries,
A configuration is used in which a power generating element is constructed by stacking a sheet-shaped positive electrode and a negative electrode with a separator interposed therebetween, and further winding them together in a spiral shape, and storing the power generating element in a battery can.

When producing the above-mentioned positive electrode, usually, for example, an aqueous Teflon dispersion as a binder and an appropriate amount of water are added to an active material made of manganese dioxide as a main component mixed with graphite, acetylene black, etc. as a conductive agent. A slurry-like positive electrode mixture is made by kneading for a certain period of time, and after applying this slurry-like mixture to a current collector, water is removed and dried in a hot air drying oven, etc., and then it is rolled to a predetermined thickness using a rolling roll. Procedures such as rolling are adopted.

Problems to be Solved by the Invention However, since the Teflon aqueous dispersion used as the binder in the above-mentioned prior art has weak binding horns, the manufacturing method according to the above-mentioned procedure has the following problems.

(2) The binding force between the slurry mixture containing Teflon aqueous dispersion as a binder and the current collector is weak, and the mixture peels off more easily than the current collector.

■The above slurry-like mixture has poor spreadability, so it is difficult to uniformly apply this mixture on the current collector, and there is a large variation in coating thickness. Difficult to reduce thickness.

(2) In this way, defects are likely to occur due to peeling of the mixture from the current collector or variations in the thickness of the mixture applied to the current collector, resulting in a low yield.

■It is difficult to adjust the viscosity of the slurry mixture.

(2) If the pressure during rolling with a rolling roll or the like is increased, the current collector and the mixture will separate, so this pressure cannot be increased and it is not possible to increase the density of the mixture coating film and improve the discharge performance.

The present invention provides a sheet positive electrode that has a strong binding force between the mixture and the current collector, has a uniform thickness, and has a large mixture density without such problems. The object of the present invention is to provide a method for manufacturing a shaped electrode.

In the present invention, polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and alcohol as a solvent are added and kneaded to an active material whose main component is manganese dioxide. A mixture was used, and the mixture was formed into a sheet by extrusion molding.

That is, in the method for manufacturing a sheet-like electrode of the present invention, a mixture having the above composition is integrally formed into a sheet-like electrode constituent material together with a porous current collector by extrusion molding, and this electrode constituent material is
The gist is to perform heat treatment stepwise at a temperature of 0° C. or lower, and then pressurize it by rolling, pressing, etc. to obtain a predetermined thickness and density.

In the above method, the integrally molded electrode constituent material may be subjected to rolling, pressing, etc. before heat treatment to adjust variations in molding thickness.

In that case, if the pressure during rolling or pressing is too high, there is a risk that the fluid mixture itself will be stretched and protrude from the porous current collector. It is necessary to roll or press at a pressure of Specifically, the maximum pressure may be such that the thickness becomes approximately 40% of the thickness after extrusion molding. This also applies to other manufacturing methods described below. Incidentally, such adjustment of the pressure can be easily performed by appropriately adjusting the gap between the rolls, for example, when rolling with rolls is used.

In addition, as another manufacturing method of the present invention, a current collector is inserted between two sheet-like mixtures obtained by extrusion molding a mixture having the above composition, and these are continuously laminated and integrated by rolling or pressing. After heat treatment in stages at a temperature of 300° C. or less, pressure may be applied by rolling or pressing to obtain a predetermined thickness and density.

Furthermore, as another manufacturing method of the present invention, a mixture having the above composition is extruded into a sheet shape and then cut into a predetermined size, and the sheet-like mixture pieces obtained in this way are placed on both sides of a current collector, and then rolled or These sheet-like mixture pieces and the porous current collector are laminated and integrated by pressing, and then heat-treated in stages at a temperature of 300°C or less, and then pressurized by rolling or pressing to a predetermined thickness and density. It may also be used as a configuration.

In the above mixture, the amount of polyvinyl butyral added is preferably 2 to 15% by weight based on the active material. If the amount is less than this range, it will not be possible to obtain the rubber properties necessary to form the mixture into a sheet. Furthermore, if the amount of polyvinyl butyral added is more than 15% by weight, the internal resistance of the battery will increase for reasons described later.

Further, the amount of dibutyl phthalate added is preferably 30 to 70% by weight based on the polyvinyl butyral. If it is less than 30% by weight, the mixture will not have sufficient plasticity, and if it is more than 70% by weight, it will have too much plasticity, and in either case, the mixture cannot be extruded with a smooth surface. It becomes impossible to mold.

Furthermore, as the alcohol, ethyl alcohol and other alcohols can be used. Further, the amount of alcohol to be added may be the amount necessary to impart rubber properties to the mixture after cross-crossing, as will be described later.

On the other hand, as the binder used in the mixture, polyvinyl butyral and an emulsified product obtained by adding alcohol such as ethanol to Teflon aqueous dispersion and stirring may be used to further enhance the binder effect. can be improved. Note that when this emulsion is added as a binder, the amount of polyvinyl butyral used must be adjusted because there is a risk of increasing internal resistance in the electrode.

When adding alcohol to the Teflon aqueous dispersion and emulsifying it as described above, it is necessary to control the temperature of the Teflon aqueous dispersion to a temperature of 20° C. or higher. This is because if the temperature is extremely low, emulsification may take a long time or may not occur.

The amount of alcohol used is preferably about 30% by weight of the Teflon aqueous dispersion. If the amount of alcohol is small (for example, IO weight % or less), emulsification will not occur, and if it is too large (for example, 80 weight % or more), excess alcohol will synergate.

Further, as the current collector, a conductive powder coated with a conductive paint made into a slurry by adding polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and alcohol as a solvent and dried may be used. . If a current collector subjected to this treatment is used, adhesive force will be exerted by the alcohol contained in the mixture during extrusion molding, and as a result, the adhesiveness between the current collector and the mixture will be further improved. improves.

As the above conductive powder, for example, graphite or acetylene black may be used alone or in combination. As the conductive paint, for example, conductive powder 92
A mixture of % by weight (46% by weight of graphite + 46% by weight of acetylene black), 5.5% by weight of polyvinyl butyral, and 2.5% by weight of dibutyl phthalate was made into a slurry by adding an appropriate amount of alcohol as a solvent. Just use it.

Further, by the heat treatment, polyvinyl butyral, dibutyl phthalate, etc. added to the mixture are thermally decomposed, and the fluidity of the mixture is lost. This heat treatment
As mentioned above, it is necessary to raise the temperature stepwise at a temperature of 300° C. or lower. In other words, if this heat treatment is performed by increasing the temperature linearly to 300℃, the n-
This is because there is a possibility that the mixture will burn due to the heat of oxidation reaction of butyral, butyraldehyde, CO, COHO, etc.

Dibutyl phthalate first decomposes at around 150-180°C, then primary decomposition (decomposition of the side chain part) of polyvinyl butyral at 170-200°C, and secondary decomposition (decomposition of the straight chain part) at around 250°C. ) occur separately, so by raising the temperature in stages as described above, it is possible to control the above thermal decomposition reactions so that these decompositions do not occur simultaneously, and therefore, combustion of the mixture is prevented.

In the above heat treatment, dibutyl phthalate decomposes almost 100% due to thermal decomposition, but polyvinyl butyral decomposes by 30%.
Approximately 90% decomposes when thermally decomposed at temperatures up to 0°C, and the remaining 10%
is reduced to a lower molecular weight and remains in the mixture as a residue. If the amount of this residue is large, it becomes a factor of increasing the internal resistance of the battery, so the amount of polyvinyl butyral used is preferably 15% or less as described above.

In addition, in order to increase the amount of thermal decomposition, the above heat treatment was carried out for 30 minutes.
It is conceivable to carry out the process at a temperature higher than 0°C, but if the temperature is too high, there is a risk of transformation of manganese dioxide or the formation of an insulating oxide film on the surface of the current collector (usually made of stainless steel or the like). Therefore, it is necessary to limit the heat treatment temperature to 300°C or less.

Further, the heat treatment time is determined to be an appropriate time taking into account the size of the treatment tank, the thickness and capacity of the sheet-like mixture, etc. Specifically, the heat treatment may be performed for about 48 hours, for example. If the heat treatment time is set to 8 hours, for example, and the temperature is raised rapidly to shorten the thermal decomposition cycle, there is a risk that the mixture will burn. Further, even if the heat treatment is performed for example for 16 hours in a thermal decomposition cycle that does not burn the mixture, a predetermined amount of thermal decomposition (for example, 90% decomposition) cannot be ensured. Furthermore, even if the heat treatment time is increased to, for example, 96 hours, the amount that is thermally decomposed is a constant amount, so there is no point in making the heat treatment time too long.

By the way, a porous current collector such as punched metal or expanded metal can be used as the above-mentioned current collector, but from the viewpoint of preventing internal short circuits due to pars in the current collector when winding the power generation element at the same time, such a current collector may be used. It is better to use punched metal with less frizz. Further, it is preferable that base material portions (non-porous portions) are provided on both sides of the punched metal in the width direction. Providing such a base material part improves the tensile strength of the punching metal itself, and effectively prevents internal short circuits in the battery due to deformation of the punching metal when winding the power generation element, thereby improving battery safety. will improve.

Furthermore, it is preferable to emboss the punched metal because it improves the contact between the porous current collector and the mixture and increases the current value that can be taken out.

Further, by providing the porous current collector with base material portions of a predetermined size at regular intervals, it becomes possible to weld the connecting plate to the current collector and scrape off the mixture therefor easily and accurately.

Effects> By adding polyvinyl butyral and kneading it with alcohol as described above, rubber properties are added to the mixture, making it possible to easily form it into a sheet by extrusion molding or the like.

Furthermore, by adding dibutyl phthalate, the mixture can be given plasticity and moldability can be stabilized.

Furthermore, by applying pressure as described above after heat treatment, voids in the mixture caused by decomposition of polyvinyl butyral etc. during heat treatment are eliminated, and it is also easy to adjust the thickness of the mixture and increase the density of the mixture. can be done.

Example> Emulsion of manganese dioxide 80% by weight, conductive agent 7% by weight, Teflon aqueous dispersion (specific gravity 1.5, solid content 6)
(0% by weight) 3% by weight, 6.5% by weight of polyvinyl butyral, and 3.5% by weight of dibutyl phthalate were mixed with an appropriate amount of alcohol, and the mixture was kneaded for 1 hour to obtain a mixture having rubber properties. .

In addition, the above emulsion was prepared by adding a total of 40% alcohol to a Teflon aqueous dispersion heated to 30°C.
The solution obtained by adding the solution in an amount of 1.0 ml and repeating stirring was used.

Next, as shown in FIG. 1, the above mixture 1 is put into an extrusion molding machine 2 equipped with a 45° crosshead, and within this crosshead, the mixture 1 and a porous current collector 3 made of stainless steel punching metal are formed. A sheet-like electrode structure 4 was obtained by integrally molding the mixture 1 on both sides of the porous current collector 3. This electrode constituent material is rolled with a rolling roll at a compression ratio of 10 to 20% to adjust the variation in molding thickness, and then wound up with a winder with a Teflon resin sheet interposed therebetween. Note that as the extrusion molding machine, one having a pressure die, a tube die, or the like can be used as appropriate.

The electrode constituent material wound up in this way is put into a drying oven, and the second
The temperature is raised stepwise from 50 to 300°C over 48 hours using the temperature cycle shown in the figure to thermally decompose polyvinyl butyral, dibutyl phthalate, etc. in the mixture. after that,
It is rolled with a rolling roll or press at a compression ratio of 20 to 50% (the compression ratio varies due to variations in the thickness before compression) to obtain a sheet-like electrode of a predetermined thickness and density.

The sheet-like electrode thus produced was cut into a predetermined τJ method and used as a positive electrode. Incidentally, the sheet-shaped electrode constituent material may be cut into a predetermined size at any time after the above-mentioned integral molding.

Then, using this positive electrode and a negative electrode made of lithium sheet, the positive electrode and negative electrode are stacked together via a separator and spirally wound to form a power generation element, and this power generation element is stored in battery t-i. In this way, a lithium-manganese battery (product of the present invention) according to the present invention having a diameter of +7 mr@ and a height of 33.5 mm as shown in FIG. 3 was manufactured. In Figure 3, 5 to 7 are the positive electrode, separator, negative electrode, and 8 to 7, respectively.
11 is a battery can, an insulating gasket, a connecting plate, a sealing plate, and 12. 13 is a lead terminal.

On the other hand, a slurry-like mixture was made with the same composition except that Teflon aqueous dispersion and water were used in place of the emulsion of Teflon aqueous dispersion, polyvinyl butyral, dibutyl phthalate, and alcohol. After coating and drying the porous current collector, it was rolled and crimped to a predetermined thickness with a rolling roll to produce a sheet-like electrode. Then, a lithium-manganese battery (conventional product), which was the same as the product of the present invention except that this sheet-like electrode was used as a positive electrode, was produced.

The yields (%) of positive electrodes in these batteries are shown in Table 1. In the case of conventional products, there are many defects due to peeling of the mixture from the porous current collector and variations in the thickness of the mixture applied to the porous current collector, and the yield is low.

Table 1 These batteries were also tested at temperatures of 20°C and -20°C after manufacture, with a resistance of 750Ω and a final voltage of 2,0V.
The discharge time of each battery when it was continuously discharged until ΔP1 was determined. The results are shown in Table 2. Note that this result was expressed as a value with the discharge time of the conventional product set as 100.

Table 2 also shows that these batteries have a temperature of 40 to 12
It was stored for 0 days, and after 40 days, 80 days, and 120 days, the temperature was 20°C and -20°C, respectively.
The discharge time of each battery was determined when the battery was continuously discharged at a temperature of 750Ω to a final voltage of 2.0μ. The results are shown in Table 3, with the initial discharge time of the conventional product set as 100.

Table 3 and FIG. 4 explain another method for producing a sheet electrode according to the present invention, in which manganese dioxide, a conductive agent, an aqueous Teflon dispersion or an emulsion thereof, polyvinyl butyral, and dibutyl phthalate are used. An appropriate amount of alcohol is mixed and the kneaded mixture is put into two extrusion molding machines 14 as shown in FIG. 15, and these extruders 14. 15 to 1 sheet mixture each
6. 17 and is extruded.

Thereafter, the sheet-like porous current collector 18 sent out from the delivery roll is inserted between the sheet-like mixtures te, 17, and these sheet-like mixtures 16.
17 and the porous current collector 18 are integrally and continuously rolled and laminated to form a sheet-like electrode constituent material 20.

After winding up the electrode constituent material obtained in this way, it is heated in a drying oven or the like in a stepwise manner as described above and then heat-treated, and then pressurized with a rolling roll or press to obtain a sheet-like electrode of a predetermined thickness and density. This is then cut to a predetermined size and used as a positive electrode. Incidentally, the sheet-shaped electrode constituent material may be cut into a predetermined size at any time after the above-mentioned lamination and integration.

Furthermore, the above mixture is formed into a sheet of only the mixture using an extrusion molding machine, and then cut into a predetermined size, and a current collector cut into a predetermined size is interposed between the two sheet-like mixture pieces thus made. A sheet-like electrode may be produced by applying pressure-bonding using a rolling roll or a press, and otherwise performing the same steps as above.

In addition, in the extrusion molding described above, by providing a known play force plate and/or screen mesh between the extruder and the crosshead, the particle size of the mixture can be adjusted, and the binder in the mixture can be adjusted. As a result of being able to remove lumps, etc., moldability is stabilized, and streaks and cracks in the sheet-like mixture due to clogging of the mixture at the crosshead outlet can be prevented.

Effects of the Invention As described above, according to the present invention, it is possible to easily produce a sheet-like electrode that has a strong binding force between the mixture and the current collector, has a uniform thickness, and has a large mixture density. be able to.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of extrusion molding in the manufacturing method of the example, Fig. 2 is a graph showing an example of heat treatment in this manufacturing method, Fig. 3 is a cross-sectional view of the battery of the example, and Fig. 4 is another example. FIG. 1...mixture, 2, 14. 15...extrusion molding machine,
3.18... Porous current collector, 5... Positive electrode, 6...
Separator, 7... negative electrode, 8... battery can. Figure 1

Claims (1)

[Claims] 1. Extrusion molding of a mixture obtained by adding and kneading polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and alcohol as a solvent to an active material whose main component is manganese dioxide. The electrode component is integrally molded into a sheet-like electrode component together with the current collector, and this electrode component is heat-treated by increasing the temperature stepwise at a temperature of 300°C or less, and then pressurized to a predetermined thickness and density. A method for manufacturing a sheet-like electrode, characterized by: 2. A current collector is inserted between two sheet-like mixtures obtained by extrusion molding the mixture according to claim 1, and these are continuously laminated and integrated by rolling or pressing, and then at 300 ° C or less 1. A method for producing a sheet-like electrode, which comprises heat-treating the electrode by increasing the temperature in steps, and then pressurizing the electrode to a predetermined thickness and density. 3. The mixture according to claim 1 is extruded into a sheet shape and then cut into a predetermined size, the sheet mixture pieces thus obtained are placed on both sides of a current collector, and the sheet mixture is rolled or pressed. The agent piece and the current collector are laminated and integrated, and then heat treated by raising the temperature stepwise at a temperature of 300°C or less, and then pressurized to a predetermined thickness and density. A method for manufacturing a sheet-like electrode. 4. The amount of the polyvinyl butyral added is 2 to 15% by weight based on the positive electrode active material, and the amount of dibutyl phthalate added is 3% by weight based on the polyvinyl butyral.
The manufacturing method according to claim 1, 2 or 3, characterized in that the content is 0 to 70% by weight. 5. As the binder, polyvinyl butyral,
4. The manufacturing method according to claim 1, wherein an emulsion obtained by adding alcohol to a Teflon aqueous dispersion and stirring the mixture is used. 6. The conductor is characterized by using a conductive powder prepared by adding polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and alcohol as a solvent and applying and drying a conductive paint in the form of a slurry. The manufacturing method according to claim 1, 2 or 3.