JP3151027B2 - Method of manufacturing coin-shaped lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a coin-type lithium secondary battery which prevents the thickness of the whole battery from exceeding a specified value due to the curvature of a negative electrode.

[0002]

2. Description of the Related Art A coin-type lithium secondary battery has a positive electrode,
It is composed of a lithium negative electrode, a separator and a non-aqueous electrolyte interposed between the positive and negative electrodes, and these are housed in a coin case.

[0003] As the lithium negative electrode, an alloy of aluminum is used. As this alloying method, there is a method of completing a lithium-aluminum alloy constituting a negative electrode in a case. In this method, generally, an aluminum plate is crimped on the current collecting surface of the negative electrode case, and then a lithium plate is crimped on the aluminum plate, and alloyed in the case by aging.

However, because of the laminated structure of the aluminum plate and the lithium plate, the negative electrode is curved with the expansion of the lithium-aluminum alloy, and as a result, the thickness of the case is increased and the thickness of the whole battery is regulated. When the negative electrode is separated from the current collecting surface, the battery performance deteriorates.

As a countermeasure against this, conventionally, a. For example, as disclosed in JP-A-62-123663,
A method using a three-layer structure in which a lithium plate is laminated on top and bottom of an aluminum plate, b. As disclosed in JP-A-3-110756, a method of forcibly alloying an aluminum plate and a lithium plate by heat treatment after lamination, and c. As disclosed in Japanese Utility Model Application Laid-Open No. 2-119354, a method of engraving a groove on a surface opposite to a surface on which expansion or contraction occurs has been proposed.

[0006] However, these methods have the following problems.

[0007]

SUMMARY OF THE INVENTION That is, a. In the above method, the process is complicated due to the three-layer structure, and the sticking of the lithium and the jig for crimping occurs on both sides, so that it is difficult to handle and there is a limitation in manufacturing. Further, since no consideration is given to the relationship between the thickness of the lithium plate and the thickness of the aluminum plate, the curvature of the negative electrode cannot be prevented fundamentally.

[0008] b. In the method (2), heating is performed at 300 to 400 ° C., which is equal to or higher than the melting point of lithium (180 ° C.), so that an oxide film is easily formed, and the incorporation of oxygen and moisture in the manufacturing atmosphere must be minimized. In addition, the cycle characteristics of the battery produced by this method were inferior to those of the battery which was alloyed by bonding lithium and aluminum left in the battery.

Further, c. In the method (1), although the curvature of the negative electrode can be suppressed to some extent, the process is complicated, and a loss in electric capacity occurs due to the formation of the groove.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to control the thickness ratio of an aluminum plate and a lithium plate constituting a negative electrode so as to reduce the curvature of the negative electrode when alloying aluminum. An object of the present invention is to provide a coin-type lithium secondary battery manufacturing method that does not cause any inconvenience.

[0011]

In order to achieve the above object, the present invention provides a method of manufacturing a coin-shaped lithium secondary battery having a height of 3 mm or more for completing a lithium-aluminum alloy constituting a negative electrode in a case. Inside the negative electrode case
After welding and integrating a current collecting net on the bottom surface, a step of pressing an aluminum plate on the current collecting surface, and then pressing a lithium plate on the aluminum plate, wherein the thickness of the aluminum plate is the thickness of the lithium plate It is characterized by being in the range of 2 to 5 times.

[0012]

The alloying process is carried out by intrusion of lithium into aluminum. The alloyed portion near the boundary between aluminum and lithium expands, and the aluminum portion not involved in the reaction does not expand. If the thickness is more than a certain value, no bending is caused by the bending stiffness of the aluminum portion, or the bending is suppressed to a negligible level. Coin shape of height 3mm or more
In a lithium secondary battery, this value is a minimum thickness of the aluminum plate in the plate thickness ratio is confirmed that it is sufficient twice the thickness of the lithium plate. Also, if it is more than 5 times thicker,
Since the capacity of the negative electrode active material, which depends only on the amount of lithium, is insufficient and battery characteristics are affected, the ratio is preferably in the range of 2 to 5 times.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. 1A to 1E show a procedure for manufacturing a coin-type lithium secondary battery according to the present invention. First, in (a), a current collecting net 2 made of stainless steel or the like is previously integrated with the inner bottom surface of the negative electrode case 1 by welding . As shown in (b) and (c), an aluminum plate 3 formed into a pellet is press-pressed at a pressure of 3 t on the current collecting net 2 and then the aluminum plate 3 is pressed.
A lithium plate 4 formed in a pellet shape is pressed at a pressure of 20 kg.
And press-bonding.

At this time, by setting the thickness of the aluminum plate 3 to a range of 2 to 5 times the thickness of the lithium plate 4, the thickness of the battery is not increased in the later alloying. That is, the alloying process is carried out by infiltration of lithium into aluminum, the alloyed portion near the boundary between aluminum and lithium expands, and the aluminum portion that does not participate in the reaction does not expand. If the thickness is greater than a certain value, the bending of the negative electrode is not caused at all by the bending rigidity of the aluminum portion, or is suppressed to a negligible level. This value is a minimum thickness of the aluminum plate by plate thickness ratio be sufficient if 2 times the thickness of the lithium plate, has been confirmed by measurements described below.
If the thickness is more than 5 times, the battery characteristics are affected. Therefore, the ratio is preferably in the range of 2 to 5 times.

Apart from the above steps, as shown in FIG. 1D, a positive electrode case 6 having a current collecting net 5 integrated with the inner bottom surface is provided.
A positive electrode 7 formed in the shape of a pellet is disposed on the inner bottom surface, a separator 8 is disposed on the upper surface, and an electrolyte solution is absorbed.

The positive electrode 7 is prepared by mixing manganese dioxide doped with lithium in advance, carbon as a conductive agent and Teflon powder as a binder in a ratio of 6: 1: 0.25, granulating the mixture, and forming the mixture into pellets. Collection net 5
And dried and heat-treated.

The separator 8 has a two-layer structure in which the negative electrode side is a microporous film and the positive electrode side is a nonwoven fabric surface.

Further, as the electrolytic solution, PC + DME +
A 1: 1: 0.5 / 1 mol / l DO / LiClO ₄ is used.

Then, the negative electrode case 1 produced in the step (c) in a dry atmosphere is fitted to the positive electrode case 6 via the sealing gasket 9 and the opening of the case 6 is caulked.
As shown in (e), a coin-shaped lithium secondary battery whose inside is sealed is completed.

By leaving this battery after completion, the internal lithium plate 4 is alloyed at the boundary surface with the aluminum plate 3 to complete the lithium negative electrode. The progress of the alloying of lithium with aluminum is extremely slow to the extent that it is almost finished when the atomic ratio of both becomes 50:50, and this time is about 40 days after the completion of the battery. I have.

[0021]

In the above configuration, the ML203 in which the thickness ratio of the aluminum plate 3 and the lithium plate 4 is variously changed.
As a result of manufacturing a type 2 battery and examining the thickness after 40 days,
The measurement result of FIG. 2 was obtained. The ML2032 immediately after assembly
The average value of the thickness (total height) of the shaped battery is 3.05 mm, and the standard of the maximum thickness is 3.2 mm. As is clear from the results shown in this figure, when the thickness ratio of aluminum / lithium is less than 2.0, the thickness is extremely increased from the standard value, and the inside of the negative electrode may be curved. confirmed.
In addition, it was confirmed that the effect of the curvature of the negative electrode was remarkable as the thickness of the battery increased.

Further, in these defective products, since the negative electrode is naturally separated from the current collector, the current collecting performance of the negative electrode is impaired, and the battery characteristics are also deteriorated.

[0024]

As described in detail in the above embodiments, according to the method of manufacturing a coin-type lithium secondary battery having a height of 3 mm or more according to the present invention, the ratio of the thickness of aluminum to the thickness of lithium is reduced. By setting the range of 2 to 5 times, the thickness of the whole battery is prevented from exceeding the standard value due to the curvature of the negative electrode, and the yield can be improved. Also,
There is an advantage that the production is easier than any of the conventional methods, and there is no difficulty in production and no structural problems.

[Brief description of the drawings]

1 (a) to 1 (e) are explanatory views showing a production procedure of the present invention.

FIG. 2 is a graph showing the relationship between the aluminum / lithium plate thickness ratio of an ML2032-type battery and the battery thickness after 40 days.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode case 2 Current collection net 3 Aluminum plate 4 Lithium plate

Continuation of the front page (72) Inventor Hidetoshi Tanaka 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (56) References JP-A-4-179067 (JP, A) JP-A 64-64 12471 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02-4/04

Claims (1)

(57) [Claims] 1. A method of manufacturing a coin-shaped lithium secondary battery having a height of 3 mm or more for completing a lithium-aluminum alloy constituting a negative electrode in a case , wherein a current collecting net is welded and integrated to an inner bottom surface of the negative electrode case. ,
The aluminum plate was crimped to the current collector surface, then lithium plate comprising the step of crimping the aluminum plate, the thickness of the aluminum plate in the range of 2-5 times the thickness of the lithium plate, the said Of manufacturing a coin-shaped lithium secondary battery.