JPH0594820A - Organic electrolyte battery - Google Patents

Abstract

(57) [Summary] [Purpose] A high-performance organic electrolyte with improved discharge characteristics and improved productivity by increasing the mechanical strength of the molded positive electrode by optimizing the composition and molding density of the positive electrode mixture. The purpose is to provide a battery. The organic electrolyte battery of the present invention is a mixture mainly composed of manganese dioxide as an active material, graphite as a conductive agent, and tetrafluoroethylene-hexafluoropropylene copolymer as a binder. Using a positive electrode mixture obtained by pressure molding a material, the compounding ratio of the graphite in the positive electrode mixture is 0.5 to 25% by weight,
The compounding ratio of the tetrafluoroethylene-hexafluoropropylene copolymer is 0.5 to 5% by weight, and the molding density of the positive electrode mixture is the bulk density of the mixed material of 2.
4 to 3 times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte battery, and in particular, a light metal such as lithium and sodium as a negative electrode active material, manganese dioxide, graphite fluoride and the like as a positive electrode active material, and lithium perchlorate and boron as electrolytes. The present invention relates to an organic electrolyte lithium battery in which a positive electrode is improved by using a simple substance or a mixed solution of propylene carbonate, dimethoxyethane, γ-butyrolactone and the like in which lithium fluoride or the like is dissolved, as an electrolytic solution.

[0002]

2. Description of the Related Art In lithium batteries such as inside-out type and coin type, manganese dioxide, which is an active material, is mixed with graphite as a conductive agent and polytetrafluoroethylene as a binder, and then mixed powder ( Hereinafter, the mixed positive electrode material powder is referred to as a mixture)
A positive electrode mixture obtained by pressure-molding is used. As the positive electrode mixture thus pressure-molded, conventionally, a mixture having a molding density of about twice the bulk density of a mixed material such as an active material, a conductive agent and a binder has been used.

That is, conventionally, from the viewpoint that the more the amount of the electrolytic solution is, the better the discharge characteristics of the battery are, the positive electrode mixture is loosely molded within a range in which the strength does not hinder the assembly process of the battery.
The molding density of the positive electrode mixture is lowered, and the liquid absorbing property of the positive electrode mixture is improved to absorb a large amount of the electrolytic solution. Further, a binder is used for the positive electrode mixture in order to facilitate molding.

[0004]

However, when such a positive electrode mixture having a low molding density is used, the positive electrode mixture swells remarkably during discharge and absorbs the electrolytic solution more than necessary. Therefore, the electrolyte is depleted as the discharge progresses,
There is a problem in that the internal resistance of the battery increases and the discharge characteristics suddenly deteriorate.

Further, when a polymer of tetrafluoroethylene is used as a binder in the composition of the positive electrode mixture, it is difficult to keep the molding density of the positive electrode mixture above a certain level, and the molding strength is insufficient. There is a problem that it is difficult to handle. Further, due to the property of tetrafluoroethylene, there is a problem that the specific resistance of the positive electrode mixture is easily increased and the battery characteristics are likely to be deteriorated.

The present invention is intended to solve such problems, and to provide an organic electrolyte battery in which the composition and molding density of the positive electrode mixture are optimized to improve the discharge performance and the productivity of the positive electrode mixture. To aim.

[0007]

In order to solve this problem, the organic electrolyte battery of the present invention comprises manganese dioxide as an active material, graphite as a conductive agent, and tetrafluoroethylene-hexafluoropropylene as a binder. A positive electrode mixture obtained by pressure-molding a mixed material mainly composed of a copolymer is provided, and the compounding ratio of the graphite in the positive electrode mixture is 0.5 to 25% by weight, and the tetrafluoroethylene-hexafluoro The compounding ratio of the propylene copolymer is 0.5 to 5% by weight, and the molding density of the positive electrode mixture is 2.4 of the bulk density of the mixed material mainly containing the active material, the conductive agent and the binder. % To 3 times.

[0008]

With this configuration, in the organic electrolyte battery of the present invention, by regulating the molding density of the positive electrode mixture within the above range, the swelling of the positive electrode mixture during the progress of discharge is effectively suppressed, and as a result, the positive electrode mixture is The absorption of the electrolytic solution by the agent is suppressed, and the exhaustion of the electrolytic solution between the positive electrode mixture and the negative electrode lithium is prevented.
As a result, the increase in internal resistance of the battery due to discharge is suppressed, and the discharge performance of the battery is improved.

Further, by optimizing the blending ratio of graphite and the binder in the positive electrode mixture, the conductivity of the positive electrode mixture is improved, and the discharge performance and productivity of the battery are improved. Further, by defining the graphite ratio of the positive electrode mixture and the compounding ratio of the binder within the above ranges, molding of the positive electrode mixture can be facilitated, and at the same time, the mechanical strength of the positive electrode mixture can be increased. , Can increase productivity.

[0010]

[Examples] It has been found that when the molding density of the positive electrode mixture is made higher than the conventional value, the deterioration of the discharge performance due to the synthetic expansion during the discharge can be suppressed, and the discharge performance of the battery can be improved.
Further, when tetrafluoroethylene-hexafluoropropylene copolymer was used instead of polytetrafluoroethylene as the binder of the positive electrode mixture, the molding density of the positive electrode was better than that when polytetrafluoroethylene was used. It can be increased, and the molding strength of the positive electrode mixture can be increased. It has also been found that when the positive electrode mixture is molded using the positive electrode mixture having the composition of the present invention, the value of the molding density of the positive electrode mixture / the bulk density of the mixed material is in the range of 2 to 3 times. Furthermore, when tetrafluoroethylene-hexafluoropropylene copolymer is used as a binder, the specific resistance of the positive electrode mixture can be kept low, and the increase in internal resistance of the battery due to the use of the binder can be suppressed. It was also clarified that the deterioration of discharge performance can be prevented. The present invention is based on such knowledge, and is mainly mixed with manganese dioxide as a positive electrode active material, graphite as a conductive agent, and tetrafluoroethylene-hexafluoropropylene copolymer as a binder. Using a positive electrode mixture obtained by pressure-molding the mixture, the graphite content in the positive electrode mixture is 0.5 to 25 wt%,
The compounding ratio of the tetrafluoroethylene-hexafluoropropylene copolymer is 0.5 to 5% by weight, and
The purpose is to set the molding density g / cm ³ of the positive electrode mixture to about 2.4 to 3 times the bulk density g / cm ³ of the mixed material of the positive electrode mixture (hereinafter, abbreviated as molding density / bulk density). It is a cylindrical lithium battery with an inside-out structure that In addition, the molding density / bulk density is about 2 times means that the compounding ratio of manganese dioxide should be increased and the compounding ratio of graphite and the binder should be lowered within the range of the compounding ratio of the positive electrode mixture of the present invention. Alternatively, it is possible to adjust the pressure applied during molding.

However, when the compounding ratio of graphite in the positive electrode mixture is decreased to increase the molding density, the theoretical capacity of the active material contained in the positive electrode mixture increases, but the compounding ratio of graphite decreases. As a result, the conductivity of the positive electrode mixture decreases, and the reaction of the active material in the positive electrode mixture tends to become non-uniform during the discharge reaction of the battery, resulting in an increase in the specific resistance of the reaction mixture and the battery voltage during discharge. It causes to disperse. On the other hand, in order to triple the molding density / bulk density, the compounding ratio of manganese dioxide in the positive electrode active material should be decreased, and the compounding ratio of graphite should be increased (the compounding ratio is 23% or more). Although the conductivity of the agent increases (the specific resistance decreases), the absolute amount of the active material in the positive electrode mixture decreases, which deteriorates the discharge performance of the battery. Further, as a result of the increase in the ratio of graphite in the positive electrode mixture, the moldability is improved when the mixture is pressure-molded. Therefore, the electrolyte solution is hardly absorbed by the positive electrode mixture after the battery is constructed. As a result, during the discharge reaction, the electrolyte solution in the positive electrode mixture is likely to become non-uniform, which causes variations in the battery voltage during discharge, which is a cause of battery performance degradation.

An organic electrolyte battery according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

Manganese dioxide (MnO ₂ ) and graphite (Gr), and tetrafluoroethylene-hexafluoropropylene copolymer were mixed at the compounding ratio (% by weight) shown in (Table 1) to prepare mixture A1 and As a comparative example to this example, a mixture A2 prepared by mixing manganese dioxide, graphite, and tetrafluoroethylene (TFE alone) at a compounding ratio (wt%) shown in (Table 2) is shown in FIG. 1 (a). As shown in FIG. 3, the disc-shaped mixture mixture 3 was molded by pressurizing and compressing with the disc-shaped mixture mixture upper die 1 and the disc-shaped mixture mixture lower die 2. Then, the disc-shaped mixture 3 was pulverized and further sifted, and the granulated mixture A1 (1) to (12) having a particle size of 14 to 50 mesh shown in (Table 1) and (Table 2), respectively, A2 (1) to (12) were obtained. In addition, these granulation mixtures A1 (1) to (12), A2
The bulk densities of (1) to (12) and the specific resistance of each granulation mixture are also shown in (Table 1) and (Table 2).

[0014]

[Table 1]

[0015]

[Table 2]

The specific resistance of the granulated mixture is 1 the type of cross-sectional area 1 cm ^2.
The specific resistance of the granulation mixture was determined by sandwiching 5 g of the granulation mixture and measuring the resistance of the granulation mixture when applying a pressure of 200 kg / cm ² . As is clear from (Table 1), A1
The granule mixture of (1) to (12) has a higher bulk density and lower specific resistance than any of the granule mixtures of A2 (1) to (12). This means that if the granulated mixture of A1 (1) to (12) is used in the case of a battery, the mixture density of the positive electrode can be easily kept above a certain level, and the resistance component related to the positive electrode in the battery during discharge can be A2 (1) to (12) shows that it can be lowered compared to when using the granulation mixture and is effective in improving discharge and characteristics. The reason why the resistivity of the mixture is lowered is that
The binder tetrafluoroethylene-hexafluoropropylene copolymer used in 1 (1) to (12) for the granulation mixture has a granular shape in the mixture and enters between the mixture to form a mixture of the mixture particles. While it is considered that the particles are joined, when tetrafluoroethylene is used as a binder, the tetrafluoroethylene becomes fibrous or plate-like inside the mixture and is entangled with the mixture particles to bond the mixture particles. It is thought that this is due to the spacing between particles. As a result, a gap is liable to be generated between the mixture particles during the mixture molding, resulting in a decrease in the mixture bulk specific gravity. On the other hand, when the battery is configured because the electrolyte is easily incorporated between the mixture particles, the reaction It is considered that the electrolyte solution required for upper ion transfer is likely to run short.

Next, as shown in FIG. 1 (d), each of these granulation mixes A1 and A2 is placed in the recess (i) of the hollow cylindrical mixture molding lower die 4 and the The amount of the granulated mixture incorporated was adjusted by the method. Then, from the upper surface 4a of the hollow cylindrical mixture molding lower die 4, a hollow cylindrical mixture molding upper die shown in FIG. 1 (e) having a shape corresponding to the hollow cylindrical mixture molding lower die 4 is formed. By pressurizing with a mold (punch) 5, these granulation mixtures A1 (1) to (12), A2 (1) to
As shown in Fig. 1 (f), (12) has an outer diameter of 15 mm and an inner diameter of 11
A hollow cylindrical positive electrode mixture 6 having a height of 14 mm and a height of 14 mm was pressure-molded. At this time, pressure is applied so that the punch 5 hits the compression surface B of the hollow cylindrical positive electrode mixture 6 shown in FIG. Further, the molding pressure on the compression surface B was set to 3 ton / cm ² . In this way, the hollow cylindrical positive electrode mixture (hereinafter abbreviated as positive electrode mixture) 6 is molded, and the molding density /
Various positive electrode mixtures having different bulk density ratios in the range of about 2.1 to 3.2 were prepared and evaluated. The following method was used to evaluate the difference in moldability depending on the composition of the molded positive electrode mixture. That is,
A load is applied from the direction perpendicular to the central axis of the molding mixture 6,
The strength of the molding mixture 6 at the time of molding was defined by the load value until the molding mixture 6 was broken, and the difference between the load values at the time of breaking was determined. In this case, since the pressure when the molding mixture 6 is pressure-molded and the weight of the molding mixture 6 are constant, it is considered that the difference in the load value when the molding mixture 6 is broken is due to the difference in the composition of the mixture. Be done. In addition, each of these molding mixtures 6 was used, and FIG.
Five lithium batteries each having an inside-out structure having the structure shown in were prepared. In FIG. 2, 11 is a negative electrode cap also serving as a negative electrode terminal, 12 is a safety valve, 13 is a sealing plate constituent member, 14 is a gasket, 15 is a positive electrode case also serving as a positive electrode terminal, 16 is a molded positive electrode mixture, and 17 is a negative electrode lead. , 18 is a current collector attached to the negative electrode lithium, 19
Is a negative electrode lithium formed in a cylindrical shape, 20 is a negative electrode lithium 1
A separator formed in a tubular shape so as to wrap 9 and a vinyl chloride (PVC) outer tube 21.

These molding mixtures A1 (1) to (12), A
2 (1) to (12), the ratio of the molding density / bulk density, and the load values when the mixture is broken by the load on the molding mixture are shown in (Table 3) and (Table 4).

[0019]

[Table 3]

[0020]

[Table 4]

Further, these molding mixtures A1 (1) to (1
2), A5 (1) to (12) are used to make 5 batteries each, and each of them is continuously discharged to a final voltage of 2.0V with a discharge resistance of 2.7kΩ at a temperature of 20 ° C, and their discharge duration is Examined. The results are shown in (Table 5) (average value of discharge time of 5 batteries each).

[0022]

[Table 5]

On the other hand, the molding pressure on the compression surface is 5
Various inside-out type lithium batteries were made in the same manner except that they were set to ton and ² ton / cm ^2, and these batteries were continuously discharged under the same conditions and their discharge durations were examined (test results are shown in Table 5). is there).

The above experimental results were plotted for each molding pressure by plotting the discharge duration on the vertical axis and the ratio of molding density / bulk density on the horizontal axis. The graph shown in FIG. 2 ton and 3 ton of the molding mixture A1 and A2, the data for the case where the compounding ratio of the binder is 1% is obtained). From FIG. 3, if the ratio of molding density / bulk density is about 2.4 times or more, the battery using the positive electrode mixture according to this example is more than the battery using the positive electrode mixture of the comparative composition described in the conventional example. It can be seen that good discharge performance can be obtained. From these results, good discharge performance was obtained when the molding pressure on the molding surface was 3 ton / cm ² or more and the molding density / bulk density value of the molding mixture was about 2.4 to 3.0. It can be seen that the strength of the mixture after molding is excellent.

By the way, the mixture mixture ratio at each measurement point in the graph of FIG. 3 is different. In other words, the smaller the molding density / bulk density ratio, the less conductive agent (graphite in this case). On the other hand, when molding, in order to obtain a molding mixture of a certain size The amount of the granulated mixture added, that is, the amount of the granulated mixture, is adjusted so that a molding mixture having a constant size can be obtained at a pressure of 3 tons (this can be adjusted by a molding machine). In addition, a material having a large bulk density, that is, a material having a small amount of graphite has a small amount (volume) of incorporation and a compression ratio (volume of incorporation / volume).
Molding mixture volume) is small. On the contrary, when the amount of graphite is large, the compression ratio becomes large. As a result, the ratio of the molding density / bulk density becomes large because the decrease in the bulk density is larger than the decrease in the molding density due to the increase in the amount of graphite.

At this time, the weight of the molding mixture is different at each point, and the theoretical capacity of the positive electrode decreases as the amount of graphite increases, but the conductivity of the mixture is improved by that much, resulting in better battery performance. .. Further, the above is an example of a cylindrical lithium battery, but in addition, for example, the present invention is applied to a coin-shaped or button-shaped lithium battery, and a disk-shaped positive electrode mixture used in this battery is similarly pressure-molded. It is clear that the same result can be obtained when the above is done. The above is an example of using a positive electrode mixture prepared by pressure molding a granulated mixture, but in addition to this, a mixed mixture was weighed without granulation and prepared by pressure molding. Similar results were obtained when the positive electrode mixture was used.

[0027]

As is clear from the above description of the embodiments, according to the organic electrolyte battery of the present invention, the swelling of the positive electrode mixture during the progress of discharge is effectively suppressed, and therefore the internal resistance due to discharge is increased. It is possible to suppress the rise and improve the discharge performance of the battery, and at the same time, it is possible to obtain sufficient strength at the time of molding the mixture. Therefore, the industrial utility value is great.

[Brief description of drawings]

FIG. 1 (a) is a perspective view of an upper mold for molding a disc-shaped mixture used for producing a granulated mixture used for producing a positive electrode mixture of an organic electrolyte battery in one example of the present invention (b). A perspective view of the lower mold (c) A perspective view of the same disk-shaped mixture (d) A perspective view of a lower mold for molding used for manufacturing the same hollow cylindrical positive electrode mixture (e) A perspective view of the same mold Figure (f) Perspective view of the same hollow cylindrical positive electrode mixture

FIG. 2 is a vertical sectional view of the lithium battery having the same inside-out structure.

FIG. 3 is a graph showing discharge characteristics of organic electrolyte batteries of one example and a comparative example of the present invention.

[Explanation of reference numerals] 1 upper mold for molding disc-shaped mixture 2 lower mold for molding disc-shaped mixture 3 disc-shaped mixture 4 lower mold for molding hollow cylindrical mixture 5 hollow cylindrical mixture Upper mold (punch) for molding 6 Hollow cylindrical mixture

Front page continuation (72) Inventor Yoshiki Terao, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Keishi Yokoyama 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A mixed material obtained by mainly mixing manganese dioxide as an active material, graphite as a conductive agent, and tetrafluoroethylene-hexafluoropropylene copolymer as a binder, was press-molded. A positive electrode mixture, wherein the graphite has a blending ratio of 0.5 to 25% by weight, and the tetrafluoroethylene-hexafluoropropylene copolymer has a blending ratio of 0.5 to 5% by weight; An organic electrolyte battery in which the molding density of the positive electrode mixture is 2.4% to 3 times the bulk density of the mixed material mainly containing the active material, the conductive agent and the binder.