JPH0558223B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a so-called bobbin-type lithium battery in which a cylindrical lithium negative electrode is housed in the center of a battery can.

<Conventional technology> As a bobbin type lithium battery as described above,
An inside-out type power generating element is known in which a power generation element, which is constructed by disposing a lithium negative electrode in the hollow part of a hollow cylindrical positive electrode mixture via a separator, is housed in a bottomed cylindrical positive electrode can.

In this type of battery, in order to prevent the lithium negative electrode from coming into contact with the positive electrode can or the positive electrode mixture at the bottom, it is necessary to isolate the lithium negative electrode bottom from the bottom of the positive square can or the bottom of the positive electrode mixture.

For this reason, conventional methods have been to wrap a nonwoven fabric sheet made of synthetic resin such as polypropylene in a cylindrical shape around the outer circumference of a lithium negative electrode formed by molding metal lithium into a cylindrical shape, or to wrap a nonwoven fabric sheet formed into a cylindrical shape around the outer periphery of a lithium negative electrode. After placing the separator on the outer periphery of the negative electrode, the end of the separator on the bottom side of the positive electrode can is bent inward over the entire circumference, and the ends are welded together by heat to close the opening at the bottom of the separator. A method has been implemented in which the bottom of the lithium negative electrode is isolated by folding the end portion around the entire circumference into the hollow part of the lithium negative electrode.

<Problems to be Solved by the Invention> However, in the case of the former method, it is necessary to bend the ends of the separator and weld the ends together after bending, which increases the number of man-hours and complicates the manufacturing process. Of course, the bottom of the separator is quite thick, and the lithium negative electrode rises from the bottom of the positive electrode can by this thickness, resulting in the creation of a portion where the positive electrode mixture and the lithium negative electrode do not face each other at the bottom of the positive electrode can. There is a problem in that the battery discharge capacity decreases accordingly.

In addition, even with the latter method, a similar non-opposing part is created, which leads to a reduction in discharge capacity. In addition, it is not easy to fold the entire circumference of the separator end into the hollow part of the lithium negative electrode, and the inner diameter of the lithium negative electrode is small, especially in small batteries. If the separator is small, the workability during folding is extremely poor, and if the separator is folded forcibly, the separator may be damaged. Another problem is that when inserting the positive electrode mixture into the hollow part of the positive electrode mixture after folding, the insertion operation must be performed carefully so that the folded part does not come off from the hollow part of the lithium negative electrode.

<Means for Solving the Problems> The method for manufacturing a bobbin-type lithium battery of the present invention, which was developed in view of the above-mentioned problems, is based on a method for manufacturing a bobbin-type lithium battery of the present invention, in which the bottom end of a separator provided at least on the outer periphery of a cylindrical lithium negative electrode is provided. A separator sheet larger than the bottom surface of the separator is placed so that the lower end surface of the lithium negative electrode is completely covered and welded or bonded, and then these are attached to a hollow cylindrical negative electrode having an inner diameter smaller than the separator sheet. The gist is to insert it into the hollow part of the mixture.

Examples of the above-mentioned cylindrical lithium negative electrode include a lithium sheet wound into a cylindrical shape and a cylindrical pressure-formed lithium metal.

In addition, as a specific example of providing a cylindrical separator around the lithium negative electrode as described above, for example, a synthetic resin nonwoven fabric sheet is wound around the negative electrode in a cylindrical shape, and the inner diameter of the separator is the same as or slightly larger than the lithium negative electrode outer diameter. There is a method in which a cylindrical separator formed into a cylindrical shape is provided on the outer periphery of the lithium negative electrode.

On the other hand, as the separator sheet, any material can be used without particular limitation as long as it is made of a material that has insulating properties in itself and is chemically stable against the non-aqueous electrolyte in the battery, but the separator ends and In terms of weldability or adhesion, it is preferable to use a material similar to that of the separator, specifically polypropylene or polyethylene. Further, the shape of the isolation sheet itself is not particularly limited as long as it can completely cover the bottom of the separator, and examples thereof include a circular shape with a larger diameter than the outer diameter of the bottom of the separator. Only one such isolation sheet may be used, but as long as it does not leave too much distance between the bottom of the positive electrode can and the lithium negative electrode when the battery is constructed by inserting it into the positive electrode mixture hollow part together with lithium and a separator. For example, two or more sheets may be stacked and used.

Further, specific means for welding the isolation sheet to the ends of the separator include a method of heating and welding the joint between the two, a method of using ultrasonic welding, impulse welding, and the like. As a specific example of bonding, a method may be used in which a PE-based hot melt resin is heated and melted and applied to at least one of the ends of the separator and the isolation sheet, and then the two are bonded. It should be noted that such welding or adhesion does not need to be performed over the entire circumference or entire surface of the bottom of the separator, but may be performed on at least a portion of the bottom of the separator.

<Function> By using the above means, the bottom of the lithium negative electrode can be isolated in one step, making the work easier, and the distance between the bottom of the lithium negative electrode and the bottom of the positive electrode can is approximately the same as the thickness of the isolation sheet itself. Therefore, the above-mentioned non-opposed portion due to the lifting of the lithium negative electrode becomes virtually negligible, and even in the case of a small battery with a small diameter, the separator will not be damaged at all.

<Examples> Examples of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1A, a separator 2 made of a polypropylene nonwoven fabric sheet wound several times in a cylindrical shape is provided around the outer periphery of a lithium negative electrode 1 made of a lithium sheet wound several times in a cylindrical shape. The bottom end 2a of the separator 2 protrudes slightly below the bottom level of the lithium negative electrode 1. It is preferable to make the end portion 2a protrude in this manner, thereby improving workability when welding (or adhering) the isolation sheet 5, which will be described next. In the figure,
3 is a negative electrode current collector crimped to the inner peripheral surface of the lithium negative electrode, and 4 is a lead body welded to the negative electrode current collector 3.

Next, as shown in FIG. 1B, a circular synthetic resin isolation sheet 5 whose outer diameter is larger than the outer diameter of the separator 2 is placed around the entire circumference of the separator end protruding from the bottom level of the lithium negative electrode. Or weld at least part of it. After welding, attach these to the first
As shown in Figure C, a short cylindrical positive electrode can 6 with a bottom is integrally formed with a projection 6a that also serves as a positive electrode terminal.
The isolation sheet 5 is inserted into the hollow part of the hollow cylindrical positive electrode mixture 7 which is compressed and stored on the inner surface of the positive electrode can until the isolation sheet 5 comes into contact with the inner bottom surface of the positive electrode can. At this time, the peripheral edge 5a of the isolation sheet 5 is bent in advance toward the outer peripheral surface of the separator as shown in the figure, and the insertion operation is performed so that the peripheral edge 5a and the inner peripheral surface of the positive electrode mixture hollow part are in contact with each other. This will make the insertion process smoother. In addition, by locating the peripheral edge 5a on the outer peripheral surface side of the separator in this way, it is possible to prevent the welded part between the separator peripheral edge and the isolation sheet 5 from peeling off during work, and also prevent the lithium negative electrode bottom surface and the inner bottom surface of the positive electrode can from peeling off during work. This can prevent the distance from increasing by the thickness of the peripheral edge portion 5a. After insertion, electrolyte is injected in the same manner as before, and the insulating gasket 8, sealing plate 9, negative terminal plate 10, and heat-shrinkable tube 11 are assembled.
By combining these, a bobbin-type lithium battery as shown in FIG. 1D can be produced.

FIG. 2 shows an example in which two isolation sheets 5 and 12 are used to improve their mechanical strength, and the upper isolation sheet 5 is attached to the bottom end of the separator 2 as before. 2a, and the lower isolation sheet 12 is welded or adhered to the isolation sheet 5.

In addition, in FIGS. 3A and 3B, a notch is provided at the bottom corner of the lithium negative electrode 13 formed by winding a lithium sheet once, so that the bottom of the negative electrode is tapered.
This figure shows an example in which the work of inserting the positive electrode mixture into the hollow part is facilitated. Examples of this type of notch include a rounded notch like the corner 13a in Figure 3A;
Examples include a straight line provided at the corner 13b in FIG. 3B.

<Effects of the Invention> According to the manufacturing method of the present invention configured as described above, the bottom part of the lithium negative electrode can be isolated in one step, reducing the number of man-hours and making the work easier. The part where the lithium negative electrode and the positive electrode mixture do not face each other at the bottom of the can can be virtually ignored, which eliminates the reduction in discharge capacity, improving battery discharge performance. It has the advantage of being completely free from damage, and is particularly useful in small-diameter batteries.

[Brief explanation of the drawing]

1A to 1D are explanatory views showing the manufacturing process of an embodiment of the present invention, FIG. 2 is an explanatory view showing one process of another example, and FIGS. 3A and B are 1 of each other example. FIG. 3 is an explanatory diagram showing the main parts of the process. 1, 13... Lithium negative electrode, 2... Separator, 5, 12... Separation sheet, 6... Positive electrode can, 7
...Positive electrode mixture.

Claims (1)

[Claims] 1. At the bottom end of a separator provided at least on the outer periphery of a cylindrical lithium negative electrode, a separator sheet larger than the shape of the bottom of the separator is placed so that the lower end surface of the lithium negative electrode is completely covered. A method for manufacturing a bobbin-type lithium battery, which comprises, after welding or adhering, inserting these into a hollow part of a hollow cylindrical negative electrode mixture having an inner diameter smaller than that of the isolation sheet.