JPH0821424B2 - Method for manufacturing rechargeable electrochemical device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method of manufacturing a rechargeable electrochemical device having a high energy density, in particular to a negative electrode.

Structure of conventional example and its problems Non-aqueous electrolyte primary batteries using lithium as a negative electrode active material and fluorocarbon, manganese dioxide, etc. as a positive electrode active material have already been put into practical use and widely used as power sources for various electronic devices. Has been. This type of non-aqueous electrolyte battery using lithium as a negative electrode is characterized by having a high voltage and a high energy density. Therefore, development of secondary batteries is also actively underway. However, it has not been put to practical use at present. The main reason is that the charge and discharge life is short,
In addition, the charging / discharging efficiency is low. This is largely due to the negative electrode.

That is, as in the case of being used in a primary battery, in a lithium negative electrode configured by crimping a plate-shaped metal lithium onto a screen-shaped current collector such as nickel, the lithium dissolved in the electrolyte is charged by discharging. Therefore, it is difficult to deposit the original plate-shaped lithium.
For example, lithium is irregularly deposited in a dendrite state by charging and is no longer used as an active material by detaching from the electrode plate, or lithium deposited in a dentrite state penetrates the separator and short-circuits in contact with the positive electrode. Or

Various attempts have heretofore been made to improve the drawbacks of such lithium negative electrodes. Among them, a method of using a certain metal or alloy having a function of occluding lithium ions in the electrolyte by charging to form an alloy with lithium by discharging and discharging lithium into the electrolyte as ions in the electrolyte by discharging is used as a negative electrode material. Considered the most promising.

Aluminum (USP3,607,4
13), silver (JP-A-56-7386, USP4,316,777, USP4,330,60
1), lead (JP-A-57-141869), tin, tin-lead alloys, etc. are known. These materials have a drawback that if the amount of stored lithium is increased by charging, the negative electrode material is pulverized and the shape of the electrode cannot be maintained.

As described above, when the negative electrode metal and lithium are brought into contact with each other in the electrolyte, the reaction occurs in a limited range where the negative electrode is in contact with the electrolyte and lithium. When aluminum is used as the negative electrode metal, pulverized LiAl is produced at the contact points of the three members, so that the negative electrode metal collapses and the function as an electrode cannot be exhibited.

In the present invention, it is used for a negative electrode which does not become fine powder even if it occludes lithium until it reaches a potential equal to that of lithium metal in the electrolyte.

A negative electrode which does not become fine powder even if it occludes lithium until it becomes equipotential with lithium metal can be confirmed by the following experiment, for example.

The same material as the electrode to be tested was used as a test electrode, and a lithium electrode having more lithium than the amount absorbed in this negative electrode material and a non-aqueous electrolyte, for example, 1 mol / liter of lithium perchlorate (LiClO ₄ ) was dissolved. It is dipped in propylene carbonate and the terminals of both electrodes are connected via a load, for example, a resistance of 1 KΩ. If left in this state, lithium is dissolved from the lithium electrode, the reaction of occluding lithium ions in the electrolyte in the alloy proceeds, and a current flows through the load. In this way, the state in which no current flows in the load, that is, the test electrode is allowed to stand until it becomes equal to the potential of the lithium electrode, and changes in the test electrode are observed.

Needless to say, it is a major premise for the negative electrode of the battery that the powder is not pulverized even if lithium is occluded in the negative electrode.

As a negative electrode that does not pulverize even if it occludes lithium,
JP 55-166871 A, 56-136462, 56-14736
No. 8 discloses an anode obtained by mixing oxides such as Cu ₂ O, TiO ₂ and Nb ₂ O ₅ , graphite and fluororesin, and press-molding them.

Furthermore, the present inventors have found that an alloy containing cadmium and / or zinc as an essential component and further containing at least one selected from the group consisting of lead, tin, indium, and bismuth has a large lithium occlusion amount and is further charged and discharged. It has been proposed that the reversible negative electrode is very promising as a rechargeable negative electrode.

When using these negative electrodes that do not pulverize even when absorbing lithium, the simplest method is to use a negative electrode and a lithium metal as described in JP-A-56-136462. This is a method in which the negative electrode assembly, which is pressure-bonded with, is placed in a battery case together with the positive electrode and the separator, and then the electrolytic solution is injected and the sealing is performed. As a result, the negative electrode and the lithium metal are short-circuited in the battery case, and lithium should naturally be occluded in the negative electrode.

However, even this method has the following problems. That is, lithium was not completely occluded in the negative electrode even when the negative electrode and lithium metal were pressure-bonded and the electrolytic solution was injected. FIG. 1 (a) is a schematic view when the TiO ₂ or alloy used for the negative electrode 1 ′ and the lithium metal 2 ′ are pressure bonded.
In this state, when the negative electrode and lithium metal are placed in the electrolytic solution,
As shown in Fig. 1 (b), a part of lithium is occluded in the negative electrode (3 'in the figure is a part of the negative electrode which occludes lithium), but a part of it is not occluded and I've been separated. This is because the electrolyte penetrates into a slight gap between the negative electrode and the surface of the lithium metal that has been crimped, and the gap between the negative electrode and the lithium metal is very small in this gap, so the resistance of the electrolyte is also small, and Reactions such as dissolution of lithium metal and occlusion of lithium in the negative electrode occur, and the reaction proceeds as if it erodes the gap between the negative electrode and the lithium metal. Finally, when the negative electrode and the portion of the lithium that was made up of the contact react with each other, electronic conductivity is lost between the negative electrode and the lithium metal, so unreacted lithium metal remains without being absorbed in the negative electrode. Will end up.

Thus, when the negative electrode and the lithium metal were simply pressure-bonded, lithium was not completely occluded and remained unreacted. The presence of this unreacted lithium reduced the charge and discharge capacity of the battery.

If lithium metal is pressure-bonded onto the negative electrode facing the positive electrode, unreacted lithium will interfere with the movement of ions in the electrolytic solution between the positive electrode and the negative electrode, which will increase the impedance of the battery. It also caused

Furthermore, in the case of a battery made by spirally winding a negative electrode assembly and a positive electrode and a separator in which only the negative electrode and lithium metal are pressure-bonded, the curvature to be coiled is different between the inside and outside of the negative electrode assembly. There was also the problem that the lithium metal would come off.

OBJECT OF THE INVENTION The object of the present invention relates to a method for manufacturing a rechargeable electrochemical device, and more particularly to a negative electrode assembly thereof, and a method for manufacturing an electrochemical device having a large charge / discharge amount and a low impedance. It is to provide a reliable and reliable manufacturing method.

The present invention is directed to a reversible positive electrode, a non-aqueous electrolyte containing lithium ions, a lithium ion in the electrolyte is stored by charging to form a compound with lithium, and lithium is discharged as an ion into the electrolyte by discharging. A method of manufacturing a rechargeable electrochemical device having a negative electrode that does not pulverize even if it occludes lithium until its potential becomes equipotential with lithium metal. A negative electrode assembly supported by an electric current collector and having electron conductivity between the current collector and a lithium metal current collector is spirally wound together with a separator and a positive electrode, and then in an electrochemical device. It is characterized in that the electrolytic solution is brought into contact with the negative electrode and the lithium metal in the device.

Description of Examples [Example for explaining technical requirements] Although it is not an electrochemical device in which a positive electrode and a negative electrode are spirally wound, both the negative electrode and the lithium metal are connected to a current collector, and electrons are transmitted through the current collector. Ensuring conductivity has a large charge / discharge amount,
It is also an example showing that it is an important requirement for manufacturing an electrochemical device having a small impedance.

As the negative electrode, a mixture consisting of 100 parts by weight of TiO ₂ , 20 parts of graphite and 20 parts of polytetrafluoroethylene in a weight ratio of 16 mm in diameter and 0.
The one that was pressure molded to 5 mm was used. As shown in the sectional view of the button type battery in FIG. 2, the negative electrode 1 was pressure-bonded to the sealing plate 4 made of stainless steel SUS304 of the battery, and further, from above, lithium having a diameter of 16 mm and a thickness of 0.12 mm was formed. The metal plate 2 was pressure-bonded so that a part of the lithium metal plate 2 was connected to the sealing plate of the button type battery. At this time, the negative electrode and the lithium metal plate used the sealing plate of the button type battery as a common collector.

For the positive electrode 5, a case is used in which a mixture of 100 parts by weight of MnO ₂ , 20 parts by weight of acetylene black and 20 parts by weight of polytetrafluoroethylene is pressure-molded to a diameter of 20 mm and a thickness of 0.7 mm. I put it in 6. Using a separator 7 using a polypropylene non-woven fabric, 1 mol / LiClO ₄ dissolved in a mixed solvent of propylene carbonate and dimethoxyethane at a volume ratio of 1: 1 was poured as an electrolytic solution and then sealed.
At this time, the amount of electricity that can be charged / discharged by TiO ₂ used for the negative electrode is 50 mA.
The amount of electricity of the lithium metal that was pressure-bonded was 50 mAh, and the amount of electricity that can be charged and discharged by the positive electrode was 100 mAh. The reason for using such a blending ratio is that the amount of electricity of the battery is determined by the negative electrode and the characteristics of the negative electrode are clearly exhibited.

After leaving for 3 days after sealing, discharge the battery at 2mA and the battery voltage becomes 1
It was carried out until it reached V, and then it was charged at 2 mA until the battery voltage reached 2V. Charging and discharging were repeated under the same conditions. The average voltage during discharge was 1.2V.

After leaving for 3 days after sealing, all the lithium metal should be occluded in TiO ₂ which is the negative electrode. The open circuit voltage and the impedance of the battery using the sealing plate as the current collector common to the negative electrode and the lithium metal of the present invention were 3.4 V and 32Ω immediately after the sealing. After left for 3 days, it is 1.5V, 32Ω,
Immediately after sealing, the potential difference between the positive electrode MnO ₂ and the lithium metal pressed onto the current collector appears, but after leaving for 3 days, the potential difference between MnO ₂ and the negative electrode lithium occluding TiO ₂ appears. Will be. The reason why the impedance did not change was that all the lithium metal was occluded in the negative electrode.

On the other hand, as a conventional example, as shown in FIG. 3, a battery was constructed in which lithium metal was simply pressure-bonded on the negative electrode.
The same elements as those in FIG. 2 are designated by the same reference numerals. However, since the lithium metal plate 3 has a different shape, it is designated as 3'in FIG. The battery of the present invention is referred to as A, and the battery having the conventional configuration is referred to as B. The negative electrode, lithium metal, positive electrode, etc. of the battery B are all the same as those of the battery A. Immediately after sealing the B battery, the open circuit voltage is 3.4V and the impedance is 32Ω, which is the same as the A battery. However, the voltage after allowing to stand for 3 days to occlude lithium in the negative electrode was 1.5 V, which was the same as that of the battery of the present invention, but the impedance was 136 Ω. When the battery was disassembled, in the battery A of the present invention, lithium was completely occluded in the negative electrode, whereas in the battery B of the conventional structure, some of the lithium metal remained in an unreacted state. , The lithium metal was not in contact with the negative electrode and was in a floating state. I think this resulted in an increase in impedance.

The discharge capacity after repeated charge and discharge cycles was 17 mAh for the battery B in comparison with 42 mAh for the battery A in the fifth cycle. This is because in battery A, almost 80% of the lithium initially charged in the battery is used for charging and discharging, whereas in battery B, approximately 40% of the lithium metal initially charged is in the negative electrode. It is thought that the reason is that 60% of the remaining battery is stored in the battery and is charged and discharged, while the remaining 60% seems to float in the battery and is no longer charged and discharged.

〔Example〕

As the negative electrode, an alloy composed of at least one selected from the group consisting of Sn, Pb, In and Bi and at least one selected from the group consisting of Cd and Zn was used.

As described above, these alloys had a large lithium occlusion amount, did not cause pulverization even when occlusion of lithium, and were excellent in reversibility of charge and discharge.

Al, Sn, Pb, In, and Bi of the alloy components of the conventional example were pulverized with the occlusion of lithium when used as the negative electrode of the experimental device. On the other hand, Cd and Zn were not pulverized, but the amount of electricity flowing to the load was small. In the above alloys, it is considered that Sn, Pb, In, and Bi are involved in the absorption of lithium, and Cd and Zn play the role of a binder for preventing pulverization.

Therefore, Sn, Pb,
It is preferable to use an alloy containing a large amount of In and Bi. However, when lithium is occluded to the same potential as lithium, the amount of Cd and / or Zn needs to be at least 5% by weight in order to prevent pulverization and further prevent pulverization due to repeated charging and discharging. Requires 10% by weight or more.

When making an alloy negative electrode, the simplest method is to immerse a mesh-shaped metal current collector of copper, nickel, iron, stainless steel, etc. in the molten alloy and pull it up to coat the alloy with the alloy. Is the way. At this time, it is desirable that the alloy contains In in order to improve compatibility between the current collector metal and the alloy. In has the ability to occlude and release lithium by charging and discharging, and if this is used, it is well compatible with the current collector,
The negative electrode has a large amount of charge and discharge. However, since In is expensive, it should be used in a small amount. In Sn-In-Cd alloy, Cd
The amount is 10 to 80% by weight, preferably 10 to 40% by weight, and the In amount is 3
A composition in which the content is -10 wt% and the balance is Sn is a preferable example. Pb−
Also in the case of In-Cd alloy, the amounts of Cd and In are preferably the same as in Sn-In-Cd alloy.

In this example, a method for manufacturing a battery will be described in which such an alloy is used as a negative electrode and is wound spirally.

When the negative electrode is wound alone or together with the positive electrode in a spiral shape, among the above alloys, an alloy having a total content of Sn, Pb, In, and Zn of 40% by weight or more is particularly soft and easy to wind.

Melt an alloy with a composition of 70% by weight of Pb, 25% by weight of Cd, and 5% by weight of In, immerse a part of the expanded nickel metal into the alloy, and pull it up to make it 14 mm x 100 mm in size and 0.2 mm in thickness. Solidified. Also, the exposed metal of this expanded metal is 14mm x 100mm, 0.4mm thick.
The above lithium plate was pressure-bonded to obtain an electrode as shown in FIG. In the figure, 8 is a nickel expanded metal of the current collector, and 9 is a nickel lead piece welded to the central portion thereof. Reference numeral 10 is a negative electrode alloy coated on the right half of the expanded metal, and 11 is a lithium metal plate pressure bonded to the left half of the expanded metal. Next, fold it from the center of the expanded metal,
Lithium was allowed to overlap the alloy. This electrode is designated as c. At this time, it is not necessary to pressure-bond the negative electrode and the lithium metal. This is because the current collector ensures electron conductivity between the negative electrode and the lithium metal.

As a conventional example, an electrode was prepared by crimping a lithium plate of the same size on an alloy of the same size as described above. This electrode is designated as d. In the electrode of d, the nickel expanded metal is buried in the alloy, and the crimped lithium metal does not come into contact with the nickel expanded metal. Therefore, the nickel expanded metal is not a collector of lithium metal.

Further, as a conventional example, an electrode f having the same configuration as the electrodes e and d having the same configuration as that of c was made by using Al and lithium metal having the same dimensions as those described above.

The positive electrode is TiS ₂ 100g, acetylene black 10g, binder 1
0 g was mixed and molded on both surfaces of titanium expanded metal, and the size was 16 mm × 130 mm and the thickness was 1 mm. The theoretical capacity of this positive electrode is 414 mAh.

A polypropylene non-woven fabric was wound around the positive electrode, superposed on the above electrode, and then spirally wound into a battery case. After this, as the electrolyte, 1 mol / LiClO ₄
After injecting propylene carbonate in which was dissolved, the mixture was sealed. A battery using the electrode c is designated as C, and batteries using the electrodes d, e, f are designated as D, E, F, respectively.

FIG. 5 shows the structure of the battery C. 12 is a groove provided on the upper part of the case 13, 14 is a sealing plate made of synthetic resin, an aluminum rivet terminal 15 is fixed in the center, and the positive electrode terminal cap 16 and the lower part are provided on the terminal 15. A positive electrode lead piece 17 is welded to each. Reference numeral 18 is an alloy resin bottom insulating plate, 19 is a spiral electrode group incorporated in the case 13, and the positive electrode 20 is wrapped with the separator 7.
And a negative electrode assembly spirally wound. Positive electrode
20 is a titanium expanded metal 21 as a current collector and a titanium lead welded to the end of this expanded metal
With 17 and.

In order to occlude lithium in the negative electrode alloy in the battery, it was left for 1 day after sealing. After that, the battery was discharged at a current of 50 mA until the battery voltage became 0.8 V, and the battery was repeatedly charged and discharged until it reached 2.5 V. FIG. 6 shows batteries C to
The discharge electricity quantity in each cycle of F was plotted and shown.

Comparing C and D, C has a larger discharge capacity. The impedance of C was smaller. This is because in the case of D, when the spiral winding was carried out, the negative electrode and lithium were only pressure-bonded, and a part was peeled off. The pressure-bonded lithium was occluded by the negative electrode from the pressure-bonded surface. It is thought that it is because it became to float from above and remained without being occluded in the negative electrode.

Batteries E and F could hardly be charged and discharged. When the battery was disassembled, in Battery E, Al was in a mud-like form and the generated LiAl was hardly collected. On the other hand, in battery F, although the Al surface is muddy,
Or, lithium remained unreacted and remained considerably. This is because lithium was separated from Al as it was occluded in Al.

As described above, even when the negative electrode assembly is wound in a spiral shape, the negative electrode current collector and the lithium current collector may be commonly used to obtain electronic conductivity between the negative electrode and the lithium metal. The amount of charge and discharge of the battery increases.

Further, as a method of obtaining electronic conductivity between the negative electrode current collector and the lithium metal current collector, in addition to using the common current collector described above, a negative electrode current collector and a lithium metal current collector are used. A method of directly welding the body or welding both current collectors through a metal piece is also effective.

As the positive electrode for forming the rechargeable electrochemical device of the present invention, one having reversibility of charge and discharge is used.
For example, MoO ₃ , TiS ₂ , V ₆ O ₁₃ , Cr ₃ O ₈ , TiO ₂ , WO ₃ , TaS ₂ , NaCrS ₂
It is a positive electrode using as an active material.

Further, if a well-known carbonaceous electrode such as a graphite electrode or an activated carbon electrode used in an electric double layer capacitor is used, it can be used as a power source for memory backup.

An organic electrolyte is suitable as the non-aqueous electrolyte. As the organic solvent, propylene carbonate, γ-butyrolactone, ethylene carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, etc., and as a solute lithium salt, LiClO 4. ₄ , LiBF ₄ , LiAsF ₆ , LiSO ₃ CF ₃ , LiPF ₆
Known materials used for organic electrolyte batteries can be used. These organic solvents and solutes are not limited to being used alone, but may be used as a mixture of plural kinds.

As the negative electrode, in addition to the alloys and TiO ₂ described in the examples,
Oxides such as Nb ₂ O ₅ , Fe ₂ O ₃ , and WO ₂ are also effective, but the alloy is the best in terms of the charge / discharge amount per volume of the negative electrode.

In the above examples, the electrochemical device in which the specific oxide, the negative electrode made of an alloy, the positive electrode and the electrolyte are combined has been described, but the present invention is not limited thereto.

As described above, in the present invention, by combining the negative electrode and the lithium alloy to form a negative electrode assembly, it is possible to make an electrochemical device having a large charge / discharge amount and a small impedance, and the industrial effect is Is large.

[Brief description of drawings]

FIG. 1 is a schematic view showing a change when the negative electrode and lithium metal are pressure-bonded and then placed in an electrolytic solution, and FIG. 2 is a cross-sectional view of a button type battery used for explaining the gist of the present invention, FIG. 3 is a sectional view of a button type battery having a conventional configuration corresponding to FIG.
FIG. 4 is a configuration diagram of a negative electrode assembly of a battery wound in a spiral shape in an embodiment of the present invention, FIG. 5 is a sectional view of the spirally assembled battery, and FIG. 6 is a cycle-discharge electricity quantity of the battery. It is a characteristic diagram. 1 ... Negative electrode, 2 ... Lithium electrode, 4 ... Sealing plate, 5 ...
… Positive electrode, 7… Separator, 8… Expanded metal, 9… Nickel expanded metal, 10… Alloy negative electrode, 11… Lithium metal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Iijima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-60-235372 (JP, A)

Claims (3)

[Claims] 1. A reversible positive electrode, a non-aqueous electrolyte containing lithium ions, and a negative electrode that absorbs lithium ions in the electrolyte to form a compound with lithium by charging and discharges lithium into the electrolyte as ions. A method of manufacturing a rechargeable electrochemical device having a negative electrode, wherein the negative electrode does not pulverize even if it occludes lithium until its potential becomes equipotential with lithium metal, and the negative electrode is supported. A negative electrode assembly having electron conductivity between a current collector that supports lithium metal and a current collector that supports lithium metal is spirally wound together with a separator and a positive electrode, and then assembled into an electrochemical device. A method of manufacturing a rechargeable electrochemical device featuring. 2. The negative electrode current collector and the lithium metal current collector are common metal current collectors, and the negative electrode and lithium metal are supported by the common current collector. A method of manufacturing a rechargeable electrochemical device according to claim 1. 3. The method for producing a rechargeable electrochemical device according to claim 1, wherein a current collector of the negative electrode and a current collector of lithium metal are welded.