JPS635180Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a battery using a positive electrode ring that covers the outer peripheral surface of a positive electrode mixture in a flat battery.
The object of the present invention is to provide a battery that has improved discharge characteristics at relatively large currents and has excellent discharge voltage stability under various discharge conditions, as well as excellent reliability and productivity.

FIG. 1 shows a cross-sectional view of a flat lithium battery as a conventional example. In this figure, 1
2 is a positive electrode case made of stainless steel, 2 is a disk-shaped positive electrode mixture whose main active material is manganese dioxide,
3 is a stainless steel positive electrode ring with an L-shaped cross section that covers the outer peripheral surface of the positive electrode mixture 2, 4 is a polypropylene nonwoven fabric separator that covers the positive electrode, 5 is an impregnating agent also made of polypropylene nonwoven fabric, and 6 is a disk-shaped lithium. A negative electrode was used as an active material, 7 was a stainless steel negative electrode sealing plate, and 8 was a polypropylene gasket. The positive electrode here is made by kneading manganese dioxide that has been subjected to heating and dehydration treatment, acetylene black as a conductive agent, and fluororesin dispersion as a binder. After drying, the mixture is molded into a disk shape by pressure molding. The heat drying process was performed again. The electrolytic solution used was one in which lithium perchlorate was dissolved as a solute in a mixed solvent of propylene carbonate and 1,2 dimethoxyethane to a concentration of 1 mole/concentration. The positive electrode ring No. 3 has the external shape shown in FIG. 2, and a positive electrode mixture having an outer diameter slightly smaller than the inner diameter of the positive electrode ring is inserted and fixed under pressure. The contact resistance between the two can be kept at a low value by increasing the pressure strength or by baking a conductive coating such as colloidal carbon on the contact surface with the positive electrode mixture on the inner surface of the positive electrode ring. Next, the reason for using a positive electrode ring is as follows.
The first is its strength reinforcement function to prevent chipping and cracking of the positive electrode mixture. In the battery assembly process in actual production, the positive electrode mixture is easily destroyed by shock, pressure, vibration, etc. The positive electrode ring can reliably prevent this, and since it has sufficient mechanical strength, it not only eliminates the need to increase the amount of binder unnecessarily, but also reduces the amount of binder and increases the amount by just that amount. It is also possible to increase the amount of active material, resulting in a battery with greater strength and discharge capacity. The second reason is to maintain stable discharge characteristics. This is particularly noticeable in the case of active materials in which the increase in the positive electrode mixture due to discharge is significantly smaller than the loss in negative electrode, but for example, if the battery voltage suddenly drops during discharge and discharging becomes impossible. The phenomenon typified by can occur in batteries that do not use a positive electrode ring. The reason for this is that if the amount of increase due to expansion of the positive electrode as the discharge progresses is less than the amount of decrease of the negative electrode, the distance between the positive and negative electrodes will increase as the discharge progresses, and the electrolyte will intervene between the two electrodes and connect them. This is because if the thickness of the impregnated material is exceeded, the battery reaction will stop. When a positive electrode ring is used, the outer periphery of the positive electrode mixture is completely fixed by the positive electrode ring, so the mixture does not expand in the outer peripheral direction, and all expansion is directed in the vertical direction, that is, in the direction of the negative electrode. For this reason, even when discharge progresses, the positive electrode mixture does not expand and increase, and discharge failure during discharge is relatively easy to occur in batteries, such as batteries that use manganese dioxide as the main active material, or batteries that use graphite fluoride, copper oxide, etc. as the main active material. Even when a material is discharged with a relatively weak current for a long period of time, or when discharged at high temperatures, the increase in the distance between the positive and negative electrodes is prevented as much as possible by directing all the volume increase due to discharge toward the negative electrode. , stable discharge characteristics can be maintained under any conditions. Furthermore, the use of the positive electrode ring can prevent internal short circuits caused by fine mixtures that have fallen off and separated from the outer periphery of the mixture as a result of expansion of the mixture due to discharge.

As described above, although the positive electrode ring has many advantages, there is one problem. This is because when discharging at a relatively large current, the discharge pressure is lower than when no positive electrode ring is used.
As a result of various studies, it seems that the cause of this is insufficient ability to supply electrolyte to the positive electrode reaction surface during discharge. In other words, solid oxides and fluorides such as manganese dioxide, graphite fluoride, and copper oxide are used as positive electrode active materials.
In lithium batteries that use a non-aqueous electrolyte such as an organic electrolyte, the battery discharge reaction is a one-way transfer reaction of lithium ions from the negative electrode to the positive electrode mixture, and the lithium ions move together with the solvated non-aqueous solvent. Therefore, it is apparently observed as movement of the electrolyte into the positive electrode mixture. That is, the larger the discharge current is, the more intense the discharge reaction is, and therefore the amount of electrolyte transferred into the positive electrode mixture is also large. In this manner, most of the electrolyte in the battery is moved and absorbed into the positive electrode mixture when the battery discharge is almost completed. Conversely, if the required amount of electrolyte is not supplied to the positive electrode mixture reaction surface during discharge, diffusion polarization based on the concentration gradient of lithium ions will occur between the positive and negative electrodes, and the discharge pressure will depend on this diffusion polarization. only decreases. This polarization is larger as the current discharges, and the lithium ions necessary for the reaction,
In other words, that amount of electrolyte is required. In the battery using the positive electrode ring shown in Figure 2, the outer peripheral surface of the positive electrode mixture is covered with the positive electrode ring 3 as shown in Figure 1, so that the electrolyte cannot be supplied from the outer peripheral part of the mixture to the inside of the mixture. , is insufficient compared to a mixture that does not use a positive electrode ring, and it is thought that this difference in electrolyte supply ability appears as a decrease in discharge pressure. Several attempts have been made to improve this point. FIGS. 3 and 4 show an example thereof. FIG. 3 shows an example in which a notch 3a is provided on the upper part of the outer peripheral surface of the positive electrode ring 3, and FIG.
This is an example in which a through hole 3b is provided on the outer circumferential surface of.

Batteries using these cathode rings show some improvement in discharge pressure, but for example, the cathode ring completely suppresses the cathode mixture that expands in the outer circumferential direction due to discharge, and all of the expansion is absorbed by the cathode ring. It is structurally insufficient to orient the negative electrode lithium in the vertical direction due to the cutout or through hole, and it is difficult to fully demonstrate the effect of the positive electrode ring. For this reason, the function of the positive electrode ring mentioned earlier, that is, under discharge conditions where the amount of expansion of the positive electrode during discharge is relatively small, such as long-term discharge with a weak current,
To maintain stable discharge characteristics at all times even during discharge at high temperatures and discharge in batteries with manganese dioxide as the main active material, or to prevent the positive electrode mixture expanding with discharge from forming in the cut portions 3a and through holes 3b.
It is not possible to completely prevent problems such as leakage and separation from the electrolyte, floating in the electrolyte, and causing minute internal short circuits.

The present invention is intended to improve these conventional drawbacks, and will be explained below using examples. FIG. 5 shows an embodiment of the present invention, in which a large number of vertical grooves 3c protruding in the inner diameter direction of the ring are formed on the side circumferential surface of a positive electrode ring 3 made of metal such as stainless steel. Even if the mixture 2 is pressurized and fixed inside the ring 3, a gap still exists on the inner surface of the ring. Figure 6 shows a comparative discharge of battery A using the cathode ring according to the present invention shown in Fig. 5, conventional battery B using the cathode ring shown in Fig. 2, and battery C not using the cathode ring. It is a characteristic diagram. As can be seen from Figure 6, the discharge pressure of Battery A of the present invention is almost the same as Battery C which does not use a positive electrode ring, and has a superior discharge pressure compared to Battery B which uses a conventional positive electrode ring shown in Figure 2. Show characteristics. In addition, the positive electrode ring according to the present invention retains the advantages of the positive electrode ring mentioned earlier, namely, the function of reinforcing the strength of the positive electrode mixture or the function of maintaining stable discharge pressure during discharge under conditions where the expansion of the positive electrode mixture is small. are doing. In this way, the side circumference of the positive electrode ring shown in Fig. 5 was able to solve the problem of a decrease in discharge pressure in relatively large current discharge while retaining the advantages of the conventional positive electrode ring. Vertical groove 3 formed on the surface toward the inner diameter of the ring
This is due to c. In other words, a gap is secured between the positive electrode mixture and the inner circumferential surface of the ring by the vertical groove 3c, and this gap allows the electrolyte to infiltrate from the outer circumferential surface of the mixture toward the inside of the mixture due to discharge, in other words. It has the function of smoothing the movement of lithium ions necessary for the battery discharge reaction, and the electrolytic solution is supplied to the side surface of the positive electrode mixture through the gap. As a result, it seems possible to improve the discharge pressure as shown in FIG. Figures 7 to 9 show other embodiments of the positive electrode ring according to the present invention, and Figure 7 shows a horizontal groove 3d that protrudes inward of the ring in addition to the vertical groove 3c.
Figure 8 shows an example in which diagonal grooves 3e intersecting each other are formed in an oblique direction. Also, Fig. 9 shows a hemispherical protrusion 3f protruding toward the inside of the ring.
It is shaped like this. In either case, a groove or protrusion is in contact with the circumferential surface of the positive electrode mixture, but a gap is maintained between the mixture and the inner surface of the ring.

As mentioned above, the present invention forms a rough rough surface with grooves or protrusions on the mixture contacting surface of the positive electrode ring that covers the outer peripheral surface of the disk-shaped positive electrode mixture and holds and fixes it. By securing a gap between the inner surface of the ring and the inner surface of the ring, it has improved the problem of low discharge pressure during relatively large current discharge, which was considered a conventional drawback, while retaining the advantages of the positive electrode ring. This is superior to the conventional improved example shown in FIGS. Furthermore, since it is easy to process, the productivity of the positive electrode ring is excellent, and its value is great.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional flat battery, Fig. 2 is an external view of a conventional positive electrode ring, Figs. 3 and 4 are views showing other conventional examples of positive electrode rings, and Fig. 5 is according to the present invention. FIG. 6 is a diagram showing a discharge characteristic comparison between a battery of the present invention and a conventional battery, and FIGS. 7 to 9 are diagrams showing other embodiments of the positive electrode ring of the present invention. . 2... Positive electrode mixture, 3... Positive electrode ring, 4... Separator, 5... Impregnating agent, 3c... Vertical groove, 3d...
...Transverse groove, 3e...Oblique groove, 3f...Semispherical projection.

Claims (1)

[Claims for Utility Model Registration] (1) A separator member holding a disk-shaped positive electrode mixture and an electrolyte, and a negative electrode active material, which covers and holds the outer peripheral surface of the disk-shaped positive electrode mixture. A flat battery in which a metal positive electrode ring to be fixed has a rough surface formed by forming irregularities on the contact surface with the positive electrode mixture, and a gap is provided between the mixture and the inner surface of the ring. (2) The flat battery according to claim 1, wherein the negative electrode is made of lithium and the electrolyte is a non-aqueous electrolyte.