JPS6049565A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase charge-discharge capacity and life by using alloy of at least one of tin and lead with cadmium as a negative electrode of a secondary battery. CONSTITUTION:A secondary battery is formed using nonaqueous electrolyte, a positive electrode having charge-discharge reversibility, and a negative electrode comprising alloy which stores and releases alkali metal ion existing in electrolyte. The negative electrode alloy contains at least one of tin and lead, and 5- 50wt% cadmium, and moreover contains 20wt% or less at least one of bismuth, indium, and zinc if necessary. By using this negative electrode, a nonaqueous secondary battery having large charge-discharge capactiy per volume and long charge-discharge cycle life is provided because deterioration of the negative electrode caused formation of fine powder is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an improvement of a nonaqueous electrolyte secondary type 71i2, particularly its negative electrode.

Conventional Structures and Problems Until now, non-aqueous electrolyte secondary batteries that use all alkali metal negative electrodes such as lithium or sodium have used all-positive electrodes such as titanium disulfide (Ti52) 'FC and various intercalation compounds. Batteries have been actively developed using an organic electrolyte prepared by dissolving lithium perchlorate in an organic solvent such as propylene carbonate. A feature of this secondary battery is that by using an alkali metal for the negative electrode, the battery voltage is high and the energy density is high.

However, this type of secondary battery has not yet been put into practical use. The main reason for this is that the life of the number of photodischarges (→no cycle) is short and the charging/discharging efficiency during photodischarge is low. This is largely due to deterioration of the negative electrode. That is, current lithium negative electrodes are mainly used in which plate-shaped metallic lithium is pressed onto a screen-shaped current collector made of nickel or the like, but metallic lithium dissolves in the electrolyte as lithium ions during discharge. However, it is difficult to photoelectrically deposit this onto plate-shaped lithium as it was before discharge, and dendrite-like lithium may be generated that breaks off from the base and falls off, or it may break off from the base and fall off. Phenomena such as lithium deposited in valleys (valleys) detaching from the current collector occur. Is it charged for this reason?
The battery becomes inoperable. Furthermore, it often happens that the dendrite-like metal lithium that is generated completely penetrates the separator that separates the positive and negative electrodes and comes into contact with the positive electrode, causing a short circuit and causing the battery to lose its function.

Various methods have been tried in the past to improve these drawbacks of negative electrodes. Generally, methods have been reported in which the material of the negative electrode current collector is changed to improve its adhesion to the precipitated lithium, or an additive to prevent dendrite formation is added to the electrolyte. However, these methods are not always effective. In other words, with regard to the current collector material, it is effective against lithium, which is deposited directly on the current collector material, but if photoelectricity (deposition) is continued further, helium will be completely deposited on the precipitated lithium, and the current collector material will be The effect disappears. Furthermore, most additives are effective at the beginning of the photodischarge cycle, but as the cycle progresses, they decompose due to oxidation-reduction reactions within the battery and lose their effectiveness.

Furthermore, recently it has been proposed to use an alloy with lithium as a negative electrode. A well-known example of this is lithium-aluminum alloy.

In this case, a somewhat uniform alloy is formed, but this uniformity disappears when charging and discharging are repeated, and when the amount of lithium is increased in particular, the electrode becomes atomized and collapses. It has also been proposed to use a solid solution of silver and an alkali metal (Japanese Unexamined Patent Publication No. 7386/1986). In this case, it is said that there is no collapse like in alloying with aluminum, but the amount of lithium that alloys quickly enough is small, and metallic lithium may precipitate without being alloyed. The use of porous materials is recommended in order to prevent Therefore, charging efficiency at large currents is poor, and in alloys with a large amount of lithium, micronization due to charging and discharging is gradually accelerated, resulting in a rapid decrease in cycle life.

In addition, there are other ideas such as using a lithium-mercury alloy (Japanese Patent Application Laid-Open No. 57-98978) and using a lithium-lead alloy (
JP-A-57-141869). However, in the case of a lithium-mercury alloy, the negative electrode becomes liquid particles of mercury due to discharge, and the electrode shape is no longer maintained. In addition, in the case of lithium-lead alloy, fine powderization by photodischarge of the electrode: 1
It is more than a silver solid solution, and therefore the amount of lead in the alloy 'fc80
Although it is said that it is desirable to reduce the amount by weight, this makes it impossible to realize high energy density batteries.

Furthermore, it is also possible to use a lithium-tin alloy or a lithium-tin-lead alloy. Even when these alloys are used, as the amount of lithium that enters the alloy increases during charging, the alloy becomes finer and cannot maintain its shape as an electrode. It can be said that a practically satisfactory water electrolyte negative electrode has not yet been found.

Therefore, it is desired to develop an excellent negative electrode that has a large amount of alkali metal occlusion and that can maintain the shape of the electrode plate without becoming fine.

OBJECT OF THE INVENTION The present invention provides a non-aqueous electrolyte secondary battery that exhibits a large amount of photodischarge per unit volume by improving the negative electrode, and exhibits good characteristics such as no miniaturization and a long photodischarge life. With the goal.

Structure of the Invention The non-aqueous electrolyte secondary battery of the present invention includes a non-aqueous electrolyte containing alkali metal ions, a positive electrode having reversibility of photodischarge, and occluding alkali metal ions in the electrolyte during charging, and occluding the alkali metal ions in the electrolyte during discharging. A negative electrode made of an alloy having the function of releasing alkali metal ions into the electrolyte, the alloy comprising:
96 at least one selected from the group consisting of tin and lead
The alloy is characterized by containing ~60% by weight of cadmium i50~''R@96.

When lithium ions are used as alkali metal ions in the electrolyte, in the secondary battery of the present invention, the negative electrode alloy occludes lithium during charging and releases lithium ions into the solute during discharging. , a lithium alloy is formed at the negative electrode.

For example, an alloy consisting of lead of 80 wt.96 and cadmium of 20 wt.fIi96 [Pb(80)-Cd(20)lf,
(The photodischarge reaction at the time is as follows.

[Pb(so)-Cd(2o)]-]1-xLi+-
1-xe in the formula Pb(8o)-Cd(20)] Liz is
This shows a lead-cadmium-lithium alloy produced by charging.

In addition, as for the range of photodischarge, it is not necessary to discharge until all of the lithium occluded in the negative electrode alloy is completely released, as in Equation 1. It may be used for photodischarge.

[Pb(80)-Cd(20)]Lix-1-yL
i++yeThe present invention provides that when an alloy of at least one member selected from the group consisting of tin and lead and cadmium is used for a complete armor,
Even when charged at a high rate in a nonaqueous electrolyte containing alkali metal ions, the alkali metal is occluded in the negative electrode alloy without precipitation of the alkali metal, and upon further discharging, the occluded alkali metal becomes alkali metal with high current efficiency. This is based on the discovery that ions are released into electrolytes.

When conventional tin or lead alone or tin-lead alloy negative electrodes are used, when charging and discharging are performed at a low rate and the full charge/discharge amount is extended, the negative electrode becomes finer and cannot maintain its shape completely. Photodischarge H1 after repeated charging and discharging cycles
A sudden drop in occurs.

However, when tin, lead, -, or an alloy of tin and lead with 5% or more of cadmium added to the negative electrode,
The negative electrode does not become finer and exhibits stable characteristics even after repeated photodischarge cycles. 1. The amount of charge and discharge also increases by adding cadmium. This increase in the amount of photodischarge is
This is thought to be due to the fact that the addition of cadmium causes the alkali metal to diffuse at a high rate along the interfaces between the various metal components in the alloy and the many phases consisting of intermetallic compounds2).

DESCRIPTION OF EXAMPLES The cell shown in FIG. 1 was constructed and the characteristics of the negative electrode of various metals and alloys in non-aqueous electrolytes were investigated.

In FIG. 1, 1 is a test electrode made of the metal or alloy studied, 2 is a positive electrode made of Ti and S2 as active materials, and 3 is a lithium plate as a reference electrode. Nickel gold was used for the lead 4.6.6 of the electrode 1°2.3.

The test electrode 1 has a size of 1 CrIL x 1 as shown in Figure 2.
The nickel ribbon 4 was entirely embedded and attached as a lead in cIrL, a metal or alloy 1a having a thickness of 1 mm.

As electrolyte 7, glopylene carbonate in which 1 mol/β LiClO4 was dissolved was used. 8 is a liquid junction bridge.

In order to measure the characteristics of a metal or alloy non-aqueous electrolyte secondary battery as a negative electrode, the potential of the test electrode 1 is set to 100% with respect to the lithium reference electrode 3. Photovoltage was applied toward the cathode at a constant current of 1 mA until the voltage reached mV. Under these conditions, lithium precipitates on the test electrode (J) and enters the alloy. After the potential of the test electrode 1 reaches OmV,
It was discharged toward the anode with a constant current of mA, and then charging and discharging were repeated under the same conditions. The table shows the amount of photoelectricity and amount of discharged electricity in the 1st and 16th cycles of the alloy and metal used in test electrode 1, the efficiency divided by the amount of discharged electricity divided by the amount of electricity, and the cycle characteristics. Shown is the total discharge electricity for 16 cycles divided by the amount of electricity in the first cycle. Charge electricity amount.

It can be said that the larger the numerical values of the amount of discharged electricity, efficiency, and cycle characteristics are, the better the negative electrode is.

From the results shown in the margins below, we found that at least one selected from the group consisting of tin and lead is more effective as a negative electrode for non-aqueous electrolyte secondary batteries than the conventionally used aluminum, lead, silver, mercury, and tin-lead alloys. It can be seen that good properties can be obtained by using an alloy containing seeds and cadmium. The table also shows the negative electrode properties of the metals used to make the alloy. From this, it can be seen that the performance is better when using an alloy than when using individual metals of each component.

When used in a tin-lead alloy negative electrode, the amount of photodischarge in the first cycle was large, but as shown in the table: When photodischarge is repeated at a low rate, the amount of lithium absorbed in the alloy increases, resulting in a negative electrode. due to shedding due to micronization.

It can be seen that the amount of photodischarge in the 16th cycle is significantly reduced. This phenomenon also appeared in alloys with a cadmium content of less than 6wt.96.

Figure 3 shows the tin-cadmium alloy, lead-cadmium alloy, and tin-lead-cadmium alloy of the present invention (inside, the weight of the tin lightship is 1:1), with the content of cadmium △ being changed. This is a plot of the discharge amount in the 16th cycle when all experiments similar to the above were carried out. From this, the content of cadmium is 6-60% by weight, tin or lead,! It can be seen that the appropriate amount of tin and lead is 96 to 60% by weight.

As shown in FIG. 3, the lead-cadmium alloy is suitable for low rate charging and discharging at 1 mA. However, when high-rate photodischarge of about 3 to 5 mA is performed, the amount of photodischarge decreases.

The order of photodischarge in high rate photodischarge is: lead-tin-cadmium alloy>tin-cadmium alloy>lead hMmiI/mu alloy.

Furthermore, when these alloys were mixed with a metal selected from the group consisting of bismuth, indium, and zinc in a range of 20% by weight or less, the charge/discharge ratio was further improved.

To add these gold 1 @ J:! J, alloy This seems to be due to easier diffusion of lithium at the interface between the alloy phases.

When comparing tin-cadmium alloy, lead-cadmium alloy, and tin-lead-cadmium alloy from the viewpoint of cost, the larger the amount of lead, the more advantageous it becomes.

In the above embodiment, an example was shown in which the negative electrode completely intercalates and desorbs lithium, but in addition to lithium, alkali metals such as sodium and potassium can also be intercalated and desorbed.

In addition, the electrolyte is not limited to the organic electrolyte shown in the examples, but even when solid electrolytes such as Li5N (lithium nitride) and LiI (lithium iodide) are used, conventional aluminum, lead, and mercury can be used.

It has better properties than silver and tin-lead alloys.

Effects of the Invention As described in Section 2, the present invention makes it possible to obtain a highly reliable non-aqueous electrolyte secondary battery with a large charge/discharge amount and a long charge/discharge life.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a cell used for examining negative electrode characteristics, FIG. 2 is a longitudinal cross-sectional view of a test electrode, and FIG. 3 is a diagram showing the relationship between the cadmium content in the alloy and the amount of discharge. 1...Test electrode, 2...Positive electrode, 3...
...Reference electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 Indication of the case 1988 Patent Application No. 168329u 2 Name of the invention Non-aqueous electrolyte secondary battery 3 Relationship with the case of person making an amendment Patent application Personal address Bold Kadoma, Kadoma City, Osaka Prefecture] Oo6 Address Name (
582) Matsushita Electric Industrial Co., Ltd. Representative Toshihiko Yamashita 4 Agent 571 Address 1006 Oaza Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 5 Subject of amendment 6 Contents of amendment 0) Specification page 14 The relationship between the amount of discharged electricity in the 15th cycle when switching between the 10th line and the 11th line and the cadmium content in the alloy is shown. Figure 6 shows the cycle characteristics obtained by dividing the amount of electricity discharged in the 16th cycle by the amount of electricity discharged in the first cycle, plotted against the cadmium content in the alloy. From the cycle characteristics shown in Figure 6, it can be seen that the amount of cadmium in the alloy is more preferably 116 wt (yo) or more.The alloy composition for increasing the amount of discharged electricity is when performing high rate charging and discharging. This is different from the case of low rate charge/discharge. Considering that the amount of electricity charged and discharged is smaller in the case of low rate charge/discharge, and as it is well known that cadmium is a pollutant, 66% by weight or less is preferable. −f L, < kll, 40
It is desirable that the amount is less than % by weight. (2) Insert the following sentence between page 14, line 16 and line 17. [Figure 6 shows the amount of electricity discharged in the 16th cycle when charging and discharging were repeated at 6 mA for a lead-cadmium-indium alloy with a cadmium content of 20% by weight. Figure 7 shows a lead-cadmium-zinc alloy with 20% cadmium by weight, and Figure 8 shows a lead-tin-cadmium-bismuth alloy with 20% cadmium and 6% cadmium in a tin lightship weight ratio of 1:1. The amount of discharged electricity in the 16th cycle is shown. As described above, in the case of high rate charging and discharging, when indium, bismuth, or i-lead is added to form a multi-component alloy, the amount of electricity charged and discharged increases more markedly. The performance tends to improve as the amount of indium increases, but it is expensive, and increasing the amount of bismuth and zinc makes the alloy hard and reduces workability.
Heavy! 'it T%, it is better to set it below. (3) "Figure 3..." on page 16, lines 16-16.
・It is. ” is corrected as follows. "Figures 3 and 4 are diagrams showing the relationship between the cadmium content in the alloy and the amount of discharged electricity, Figure 6 is a diagram showing the relationship between the cadmium content in the alloy and the cycle characteristics, and Figure 6 is a diagram showing the relationship between the cadmium content in the alloy and the amount of discharged electricity. Figure 7 is a diagram showing the relationship between the indium content of a cadmium-indium alloy and the amount of discharged electricity, Figure 7 is a diagram showing the relationship between the zinc content of a tin-cadmium-zinc alloy and the amount of discharged electricity, and Figure 8 is a diagram showing the relationship between the zinc content and the amount of discharged electricity in a tin-cadmium-zinc alloy.
FIG. 3 is a diagram showing the relationship between bismuth content and discharge electricity m of a tin-cadmium-bismuth alloy. (4) Added attached drawings Figures 4, 5, 6, 7, and 8. Figure 4 shows the weight of cadmium (weight) in Figure 5. Cadmium ef (weight) in car X Figure 6. Hill) Fig. 7 δn-Ca -Zn4'tl'dalt (4t: amount
) Fig. 8 Pb-3n-Cd-13iA'4ゝψ's mass combination I
(Major IS) Procedural Amendment 1 Display of the case 1988 Patent Application No. 158329 2 Name of the invention Non-aqueous electrolyte secondary battery 3 Person making the amendment Relationship to the case Patent application Office Oaza Kadoma, Kadoma City, Osaka Prefecture 1006 address name (
582) Matsushita Electric (i; (Sangyo Co., Ltd. Representative Yamashita)
Toshihiko 4 Agent 571 Address 6, Matsushita Electric Industrial Co., Ltd., 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Contents of Amendment (1) The scope of claims column of the specification will be corrected as shown in the attached sheet. (2) Page 6 of the specification, lines 16-16, “96-...
...Weight %" is corrected to "and cadmium." (3) Insert the following sentence at the end of page 6, line 17. “A suitable content of cadmium in the alloy is 6-60% by weight.
It is. 2. Claims (1) A non-aqueous electrolyte containing alkali metal ions, a positive electrode having reversibility of charging and discharging, which absorbs alkali metal ions in the electrolyte during charging, and stores the alkali metal ions in the electrolyte during discharge. and a negative electrode made of an alloy that has the function of releasing into the air, the alloy being made of tin and lead! A non-aqueous electrolyte secondary battery characterized in that it is an alloy containing at least one member selected from FF and cadmium. (2) The nonaqueous electrolyte secondary battery according to claim 1, wherein the alloy has a cadmium content of 6 to 50% by weight. (3) The non-aqueous electrolyte secondary battery according to claim 1, wherein the alloy contains at least one selected from the group consisting of bismuth, indium, and zinc in an amount of 2% by weight or less.

Claims (1)

[Claims] (1) A nonaqueous electrolyte containing alkali metal ions, a positive electrode with reversibility of photodischarge, and photoelectricity 11! a negative electrode made of an alloy having the function of storing alkali metal ions in the electrolyte and releasing the alkali metal ions during discharge, wherein the alloy is a group consisting of tin and lead; 96 to 60 serious damage to at least one type selected from 9
6. It is an alloy containing 50 to 5% by weight of cadmium! [Non-aqueous electrolyte secondary battery with characteristics. ? 2.) The non-aqueous electrolyte secondary battery according to claim 1, wherein the alloy contains at least 2% by weight of at least one selected from the group consisting of bismuth, indium, and zinc.