JPH11126587A - Nonaqueous electrolyte secondary battery and manufacture of its sealing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery of a small-sized and lightweight construction having a large charge/discharge capacity and excellent in the dampproof characteristic and establish a method of manufacturing a sealing plate for the battery. SOLUTION: A nonaqueous electrolyte secondary battery includes a sealing plate 2 formed through single-piece molding of a clad material consisting of an aluminum alloy negative electrode 5 able to occlude lithium and emit and a different metal unable to occlude and emit lithium, wherein the aluminum alloy side of the clad material is subjected to a press working or etching so that a ring-shaped groove in recessed from is formed as having a thickness greater than that of the aluminum alloy, and this procedure is continued in reversals, and the folded-back part 2a of the sealing plate 2 is accomplished in such a structure that the different metal not capable of making lithium absorption and emission continues in a U-shape while the aluminum alloy negative electrode 5 capable of making lithium absorption and emission is in discontinuity in the folded-back bottom part 5b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte secondary battery which is small, lightweight, has a large charge / discharge capacity, and has excellent moisture resistance.

[0002]

2. Description of the Related Art A non-aqueous electrolyte battery using lithium as a negative electrode active material generally has a high voltage, has a high energy density, and is excellent in reliability such as storage stability and liquid leakage resistance.
Since it is possible to reduce the size and weight, its demand as a main power supply for various small electronic devices and a power supply for memory backup is increasing year by year. Until now, this type of battery was mainly a non-rechargeable primary battery, but recently, a rechargeable secondary battery has been developed and demand is growing.

As a rechargeable non-aqueous electrolyte secondary battery,
A battery is known in which an alloy of lithium and another metal is used as a negative electrode, a nonaqueous electrolyte is used as an electrolyte, and various positive electrodes are combined. The reason for using a lithium alloy for the negative electrode is as follows. That is, when a single lithium metal is used for the negative electrode as in the case of the primary battery, at the time of charging, lithium ions in the electrolyte are non-uniformly deposited on the surface of the negative electrode lithium and tend to form dendritic crystals. As a result, this dendrite-like crystal penetrates through the separator and contacts the positive electrode, causing an internal short circuit or an uneven discharge reaction,
In many cases, lithium in the dendrite-like crystal falls off and lithium which does not participate in charge / discharge increases, and as the charge / discharge cycle progresses, the discharge capacity decreases and the charge / discharge cycle life is often shortened. On the other hand, when a lithium alloy is used for the negative electrode, metallic lithium that precipitates during charging is electrochemically diffused and occluded in the negative electrode alloy, so that dendrite-like crystalline lithium does not precipitate on the negative electrode surface. Discharge cycle life can be improved. Aluminum, lead, bismuth, indium, tin and the like are effective metals for forming an alloy with lithium for the negative electrode of the non-aqueous electrolyte secondary battery.

On the other hand, various materials have been studied for the positive electrode. In general, materials that form intercalation compounds and crystals having a tunnel structure with lithium ions, for example, metals such as manganese dioxide, vanadium pentoxide, and niobium pentoxide Oxides and sulfides such as titanium disulfide and molybdenum disulfide are used. In addition, there are also those using conductive polymers such as polyaniline and polyacene.

FIG. 2 shows a structural example of a conventional non-aqueous electrolyte secondary battery. 2, reference numeral 1 denotes a case also serving as a positive electrode terminal, 2 denotes a sealing plate which also serves as a negative electrode terminal and has a U-shaped folded portion 2a around its periphery, 3 denotes a gasket for insulating the case 1 from the sealing plate 2, 4 denotes a positive electrode, 5 denotes a positive electrode, Denotes a negative electrode, and 6 denotes a separator for separating the positive electrode 4 and the negative electrode 5. In the above-described conventional battery configuration, the negative electrode generally employs a method in which an aluminum alloy is punched into a circular shape from a roll-formed body having an appropriate thickness, and the aluminum alloy is welded to the inner surface of the sealing plate 2, and then the aluminum alloy is doped with lithium in advance. . As shown in FIG. 2, in the conventional nonaqueous electrolyte secondary battery, the facing area between the positive electrode 4 and the negative electrode 5 is limited, so that it is difficult to increase the charge / discharge rate, and the positive electrode 4 and the negative electrode 5 In addition, since the occupied volume density of the battery element in which the separator 6 is impregnated with the non-aqueous electrolyte is not necessarily high, there is a disadvantage that it is difficult to increase the capacity as a secondary battery. Such a problem has become an important issue as the size and weight of the battery are reduced and the ratio of the internal volume to the total volume of the battery is reduced.

As one means for solving the above problems,
Some use a cladding material made of an aluminum alloy that can occlude and release lithium and a dissimilar metal that cannot occlude and release lithium, and use a sealing plate having a U-shaped folded portion at the periphery. FIG. 3 shows the structure of this battery. In FIG. 3, 1 is a case also serving as a positive electrode terminal, 2 is a sealing plate which also serves as a negative electrode terminal and has a U-shaped folded portion 2 a around its periphery, 3 is a gasket for insulating the case 1 and the sealing plate 2, 4 is a positive electrode,
Reference numeral 5 denotes a negative electrode which is closely adhered to and integrated with the sealing plate 2 by a clad, and has a negative electrode folded portion 5a on a peripheral edge. Reference numeral 6 denotes a separator for separating the positive electrode 4 from the negative electrode 5. In the negative electrode 5 of the battery having this structure, lithium is doped at the outermost periphery of the folded portion 5a of the U-shaped negative electrode by diffusion of lithium in the aluminum alloy. Folded portion 5a of U-shaped negative electrode
The outermost portion of the battery is insulated from contact with the outside air by the gasket 3. However, compared with the battery having the structure shown in FIG. It is more susceptible to moisture. When lithium in the aluminum alloy reacts with moisture in the outside air, lithium hydroxide or lithium oxide is generated, so that the amount of lithium that can participate in charge / discharge decreases and the charge / discharge capacity decreases.

Further, as another means, a clad material of an aluminum alloy capable of absorbing and releasing lithium and a dissimilar metal capable of absorbing and releasing lithium is used.
Although there has been an attempt to use a sealing plate having no letter-shaped folded portion, such a sealing plate significantly deforms the sealing plate when the battery is sealed, and is different from the conventional battery having the structure shown in FIG. It is difficult to obtain the same storage stability, liquid leakage resistance and moisture resistance.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-aqueous electrolyte secondary battery having improved charge / discharge capacity while maintaining good storage stability, liquid leakage resistance and moisture resistance of the battery. And a method of manufacturing the sealing plate.

[0009]

In order to achieve the above object, the present invention uses a clad material of an aluminum alloy negative electrode capable of inserting and extracting lithium and a dissimilar metal capable of not inserting and extracting lithium. In a non-aqueous electrolyte secondary battery using a sealing plate integrally molded and having a U-shaped folded portion at the periphery, in the peripheral folded portion of the sealing plate, a dissimilar metal that cannot occlude and release lithium is U
The aluminum alloy negative electrode connected in the shape of a letter and capable of inserting and extracting lithium has a folded portion with a discontinuous bottom.

[0010] Further, the aluminum alloy negative electrode capable of inserting and extracting lithium and a clad material of a dissimilar metal that cannot insert and remove lithium are integrally molded, and the U-shaped folded portion of the peripheral edge is used to store lithium. A dissimilar metal that cannot release is connected in a U-shape, and an aluminum alloy negative electrode that can occlude and release lithium is a method of manufacturing a sealing plate that is discontinuous at the bottom of the folded portion. The manufacturing method is such that an annular groove having a thickness greater than the thickness of the concave aluminum alloy is provided on the aluminum alloy side by pressing or etching, and then processed into a folded shape.

Further, the dissimilar metal which cannot store and release lithium is selected from the group consisting of stainless steel, titanium, iron, copper and nickel.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, a battery structure and a manufacturing method of a sealing plate described in the Means for Solving the Problems are used to generate electricity while taking advantage of the sealing plate having a U-shaped folded portion. Since the element is filled between the sealing plate and the case, the discharge capacity of the battery can be improved without lowering the moisture resistance. Furthermore, the facing area between the aluminum alloy negative electrode and the positive electrode that are in contact with the non-aqueous electrolyte is increased, and the allowable current value for charging and discharging can be increased at that ratio. The reason is as follows. In a battery configuration in which a dissimilar metal that cannot occlude and release lithium and an aluminum alloy negative electrode that can occlude and release lithium are both continuously connected in a U-shape at the peripheral folded portion of the sealing plate of the battery shown in FIG. Since the outermost peripheral portion of the U-shaped folded portion is not in contact with the non-aqueous electrolyte, when lithium doped in this portion participates in the battery reaction, the lithium in this portion comes into contact with the non-aqueous electrolyte. Only when it is diffused into the part where it is, can it participate in the battery reaction.
There is a marked difference in the reaction rate between the surface reaction and the diffusion reaction in the part in contact with the non-aqueous electrolyte, so when an ultra-low rate discharge or over-discharge occurs, the outermost part of the U-shaped folded part Even if doped lithium can participate in the reaction, the discharge capacity increases. However, in normal discharge or high-rate discharge, the diffusion reaction cannot catch up with the surface reaction, and a remarkable increase in charge / discharge capacity cannot be expected. Further, at the outermost peripheral portion of the U-shaped folded portion, lithium is doped by diffusion of lithium in the aluminum alloy. Although the outermost portion of the U-shaped folded portion is insulated from contact with the outside air by the gasket, the distance to the outside air is relatively short, so that it is easily affected by moisture in the outside air. When lithium in the aluminum alloy reacts with moisture in the outside air, lithium hydroxide or lithium oxide is generated, so that the amount of lithium that can participate in charge and discharge decreases, resulting in a decrease in charge and discharge capacity. On the other hand, in the battery configuration of the present invention, the aluminum alloy at the outermost periphery of the U-shaped folded portion is not doped with lithium, so that the distance to the outside air does not become relatively short. Therefore, since lithium doped in the aluminum alloy hardly reacts with moisture in the outside air, lithium which can participate in charge / discharge does not decrease, and the charge / discharge capacity does not decrease.

In the production of the sealing plate, the aluminum alloy negative electrode capable of inserting and extracting lithium and the aluminum alloy side of a clad material of a dissimilar metal that cannot insert and release lithium are previously pressed or etched to form a concave aluminum alloy. After forming an annular groove larger than the thickness of the battery, it is processed in a folded shape, so it has sufficient strength as a sealing plate, and it is also possible to easily process a small sealing plate. It can be achieved even more.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below using a coin-type non-aqueous electrolyte secondary battery shown in FIG. Reference numeral 1 denotes a case also serving as a positive electrode terminal, which is made of a stainless steel plate having excellent corrosion resistance. Reference numeral 2 denotes a sealing plate having a U-shaped folded portion 2a on the periphery which also serves as a negative electrode terminal, and is made of a stainless steel plate as in the case 1. Reference numeral 3 denotes a polypropylene gasket that insulates the case 1 and the sealing plate 2, and 4 denotes a positive electrode, and manganese dioxide,
A mixture obtained by mixing carbon black as a conductive agent and a copolymer of tetrafluoroethylene and hexafluoropropylene as a binder in a weight ratio of 100: 4: 8 is formed into a pellet by pressure molding. is there. Reference numeral 5 denotes a negative electrode, which is an aluminum alloy doped with lithium. The negative electrode 5 is closely adhered and integrated with the sealing plate 2 by the clad, and is discontinuous at the bottom 5b of the folded portion 5a. 6
Is a polypropylene separator for separating the positive electrode 4 and the negative electrode 5. In addition, the sealing plate 2 is formed by forming an annular groove having a thickness equal to or greater than the thickness of the concave aluminum alloy on the peripheral edge by pressing on the aluminum alloy side of the clad material of the aluminum alloy and stainless steel, and then processing it into a folded shape. As the electrolytic solution, a non-aqueous electrolytic solution in which lithium perchlorate was dissolved at a ratio of 1 mol / liter in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in an equal volume was used. As a comparative sample with the battery of the example according to the present invention, a battery having the configuration shown in FIGS.

In preparing the battery, the amount of lithium doped in 1 g of the aluminum alloy was kept constant.
Adjustment was made so that the ratio of the power generating element in the space inside the battery was constant. The batteries subjected to the test were all R2020 size (diameter 200) of the product of the present invention (A) shown in FIG. 1, the conventional product (B) shown in FIG. 2, and the comparative product (C) shown in FIG.
mm, height 2.0 mm) and the same size. Table 1 shows the open circuit voltage, internal resistance, and discharge capacity immediately after assembling these batteries.

[0016]

[Table 1]

The values shown are the average values of 20 cells for each of the product of the present invention (A), the conventional product (B) and the comparative product (C).
Internal resistance is 1kHz AC method and discharge capacity is 2mA
At a constant current of 2.0 V to obtain 2.0 V. As understood from the results in Table 1, the product of the present invention (A) and the comparative product (C) have a lower internal resistance because the facing area between the positive and negative electrodes is larger than that of the conventional product (B). Therefore, it can be expected that the allowable charging rate and discharging rate of the battery can be improved up to about 1.6 times. Also, in the discharge capacity, the occupied volume density of the battery element in the battery container is about 1.4 times as large as that of the product of the present invention (A) and the comparative product (C) than the conventional product (B). Indicated. In comparison between the product of the present invention (A) and the comparative product (C), almost no difference was observed. Theoretically, the comparative product (C) should have a larger discharge capacity than the product of the present invention (A), but there was actually no difference. this is,
Since the outermost peripheral portion of the U-shaped folded portion 5a of the comparative product (C) was not in contact with the non-aqueous electrolyte, it was suggested that lithium doped in this portion could not participate in the battery reaction. Table 2 shows the internal resistance and the discharge capacity of the batteries of the present invention (A), the conventional product (B), and the comparative product (C) when stored in a high-temperature and high-humidity room at 60 ° C.-90% RH for 40 days. This shows the deterioration rate with respect to the initial capacity. The values shown are the average values of 20 cells for each of the product of the present invention (A), the conventional product (B), and the comparative product (C), the internal resistance is 1 kHz AC method, and the deterioration rate is the number of days for each battery. It was determined from the discharge capacity (discharge to 2.0 V at a constant current of 2 mA) and the initial discharge capacity of each battery (discharge to 2.0 V at a constant current of 2 mA).

[0018]

[Table 2]

From the results shown in Table 2, the comparative product (C) has a higher internal resistance after storage than the product of the present invention (A) and the conventional product (B). This is because lithium is doped at the outermost periphery of the U-shaped folded portion 5a of the comparative product (C) due to diffusion of lithium in the aluminum alloy, and the distance between lithium and the outside air becomes relatively short. This is due to being easily affected by moisture in the outside air. Further, also in the deterioration rate of the discharge capacity with respect to the initial capacity, the active lithium in the aluminum alloy is inactivated by reacting with the moisture in the outside air for the above reason, so that lithium which can participate in charge and discharge decreases, The discharge capacity is significantly reduced.

In the embodiment, stainless steel is used as the dissimilar metal which cannot occlude and release lithium to be clad with the aluminum alloy. However, the present invention can be similarly applied using metals such as titanium, iron, copper and nickel. In addition, as the positive electrode material, vanadium pentoxide, titanium disulfide, molybdenum disulfide, molybdenum trioxide, or the like can be similarly used in addition to manganese dioxide. The present invention is not limited to the type of the non-aqueous electrolyte. Further, a method of obtaining a cladding sealing plate 2 in which a stainless metal which cannot occlude and release lithium is connected in a U-shape and an aluminum alloy negative electrode 5 which can occlude and release lithium is discontinuous at the bottom 5b of the folded portion 5a. In the example, the aluminum alloy side of the clad material was provided with an annular groove having a thickness greater than the thickness of the concave aluminum alloy by pressing and then processed into a folded shape, but in addition, the aluminum alloy side of the clad material was etched by etching. After providing an annular groove more than the thickness of the concave aluminum alloy,
The same effect can be exerted as a manufacturing method in which the folded portion 2a is formed on the peripheral edge of the sealing plate 2, and thus the anode alloy at the bottom 5b is removed by etching after the folded portion 5a of the negative electrode 5 is formed.

[0021]

As apparent from the above description, according to the present invention, an aluminum alloy negative electrode capable of absorbing and releasing lithium and a clad material of a dissimilar metal capable of absorbing and releasing lithium are integrally molded, And the periphery has a U-shaped folded portion, and the peripheral folded portion is a U-shaped dissimilar metal that cannot absorb and release lithium, and an aluminum alloy negative electrode that can absorb and release lithium is at the bottom of the folded portion. By using a discontinuous sealing plate, U
It is possible to provide a flat nonaqueous electrolyte secondary battery having improved charge / discharge capacity while utilizing the storage stability, leakage resistance and moisture resistance of a battery using a sealing plate having a letter-shaped folded portion, The method for manufacturing the sealing plate is easily realized.

[Brief description of the drawings]

FIG. 1 is a half vertical sectional view of a battery according to an embodiment of the present invention.

FIG. 2 is a half cross-sectional view of a conventional battery.

FIG. 3 is a half vertical sectional view of a comparative example battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2 Sealing plate 2a Folded part of sealing plate 3 Gasket 4 Positive electrode 5 Negative electrode 5a Negative folded part 5b Bottom part 6 Separator

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Fumio Oo 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. An aluminum alloy negative electrode capable of inserting and extracting lithium and a clad material of a dissimilar metal that is not capable of inserting and extracting lithium, are integrally molded, and have a periphery formed of U.
A sealing plate having a U-shaped folded portion, a non-aqueous electrolyte secondary battery that seals the power generating element with a gasket interposed as an insulator between both the positive electrode case and the peripheral folded portion of the sealing plate, A nonaqueous electrolyte secondary battery characterized in that dissimilar metals that cannot occlude and release lithium are connected in a U-shape, and an aluminum alloy negative electrode that can occlude and release lithium has a discontinuous bottom at the folded portion. 2. The dissimilar metal is stainless steel, titanium, iron,
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is selected from the group consisting of copper and nickel. 3. An aluminum alloy negative electrode capable of occluding and releasing lithium and a clad material of a dissimilar metal capable of occluding and releasing lithium are integrally molded and have a peripheral U-shaped member.
This is a method of manufacturing a sealing plate in which a dissimilar metal in which the folded portion of the shape cannot absorb and release lithium is connected in a U-shape and an aluminum alloy negative electrode capable of absorbing and releasing lithium is discontinuous at the bottom of the folded portion. Forming a groove having a thickness equal to or greater than the thickness of the concave aluminum alloy on the aluminum alloy side of the cladding material constituting the sealing plate by pressing or etching, and then processing the groove into a folded shape. . 4. An aluminum alloy negative electrode capable of occluding and releasing lithium and a clad material of a dissimilar metal capable of occluding and releasing lithium are integrally molded and have a peripheral U-shaped member.
This is a method of manufacturing a sealing plate in which a dissimilar metal in which the folded portion of the shape cannot absorb and release lithium is connected in a U-shape and an aluminum alloy negative electrode capable of absorbing and releasing lithium is discontinuous at the bottom of the folded portion. Forming a U-shaped folded portion around the periphery of the clad material constituting the sealing plate, and then removing the aluminum alloy layer located at the bottom of the folded portion. The method of manufacturing the board. 5. The dissimilar metal is stainless steel, titanium, iron,
5. The method for producing a sealing plate according to claim 3, wherein the sealing plate is selected from the group consisting of copper and nickel.