JPS59163757A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous electrolyte secondary battery having a high energy density and a long charge-and-dischrge life and being excellently safe and reliable by causing lithium or the like to be absorbed by a negative electrode material during charging and causing the negative electrode material to discharge lithium ion or the like into electrolyte during discharging by using an alloy consisting of two or more metals chosen from among tin, bismuth, cadmium and lead as the negative electrode material. CONSTITUTION:An alloy consisting of two or more metals chosen from among Sn, Bi, Pb and Cd is used as a negative electrode material so that it absorbs alkali metal ion contained in electrolyte during charging and discharges the absorbed alkali metal ion during discharging. At least one metal chosen from among In, Ca, Hg, Sb, Zn and Ag may be added to make the above alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the improvement of negative electrodes for non-aqueous electrolyte secondary batteries.As a result of this improvement, they have a high energy density, a long charge/discharge life, safety, and reliability. The present invention provides a rechargeable battery with excellent performance.

Structures of conventional examples and their problems Until now, non-aqueous electrolyte secondary batteries using alkali metals such as lithium and sodium as negative electrodes have been made using various intercalation compounds such as titanium disulfide (TIS2). The development of batteries that use organic electrolytes such as lithium perchlorate (L I C11O4) dissolved in organic solvents such as globylene carbonate (hereinafter abbreviated as PC), which are used as positive electrode active materials, has been actively developed. . A feature of this secondary battery is that by using lithium for the negative electrode, the battery voltage increases, resulting in a high energy density secondary battery.

However, this type of secondary battery is currently not in practical use. The main reason for this is that the life of the number of charging and discharging times (cycles) is short and the charging and discharging efficiency during charging and discharging is low. This is largely due to deterioration of the lithium negative electrode.

In other words, current lithium negative electrodes are mainly made by pressing a plate of metal lithium onto a screen-like current collector such as Ni-Nokel, but during discharge, the metal lithium dissolves into the electrolyte as lithium ions. . However, it is difficult to charge the lithium and deposit it into the plate-like lithium that it was before discharging, and dendrite-like lithium may be generated that breaks off from the base and falls off, or spherule-like (valley) lithium forms. Phenomena such as the lithium deposited on the lithium ions being desorbed from the current collector occur. This results in a battery that cannot be charged or discharged. Furthermore, the generated dendrite-like metallic lithium often 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 the formation of dendrites 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 for lithium that is deposited directly on the current collector material, but if charging (precipitation) continues further, helium will be deposited on the precipitated lithium, and the effect of the current collector material will disappear. Also, most additives are effective at the beginning of the charge/discharge cycle, but as the cycle progresses, most of them lose their effectiveness due to oxidation-reduction reactions within the battery.

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 uniform alloy is formed, but this uniformity disappears when charging and discharging are repeated, and when the amount of lithium is increased, the electrode becomes atomized and collapses. It has also been proposed to use a solid solution of alkali metal and alkali metal (Japanese Patent Application Laid-open No. 7386/1986). In this case, it is said that there is no collapse like in alloys with aluminum, but
The amount of lithium that can be alloyed quickly enough is small, and metallic lithium may precipitate without being alloyed. To prevent this, the use of porous materials is recommended. Therefore, the charging effect of large currents is poor, and in alloys with a large amount of lithium, the micronization due to charging and discharging is gradually accelerated, and the cycle life is rapidly reduced.

In addition, the idea of using a lithium-mercury alloy (Japanese Patent Application Laid-open No. 6
7-98978) + invention using lithium-lead alloy (
However, in the case of a lithium-mercury alloy, due to discharge, the negative electrode becomes smeared with liquid particles of mercury and does not retain its separated shape.In addition, in the case of a lithium-lead alloy, The fineness of the powder due to charging and discharging of the electrode is higher than that of a silver surface solution, and therefore it is said that it is desirable to keep the amount of lead in the alloy at about 80%, but this does not make it possible to realize a high energy density battery. As described above, it can be said that a practically satisfactory negative electrode for non-aqueous electrolyte secondary batteries has not yet been found.

Therefore, as an excellent negative electrode, it is desired to develop a material that can store a large amount of alkali metal and has a high release and storage rate.

Purpose of the Invention The present invention provides a non-aqueous electrolyte secondary battery that exhibits good characteristics such as a large charge/discharge capacity per unit volume and a long charge/discharge life by specifying a negative electrode material. .

Structure of the Invention The secondary battery of the present invention is characterized in that an alloy consisting of at least two metals selected from the group of tin, bismuth, cadmium, and lead is used as the negative electrode material, Lithium is occluded in the alloy, and lithium is released into the electrolyte by discharge.

Description of Examples As mentioned above, in the secondary battery of the present invention, lithium is occluded in the negative electrode material alloy by charging, and lithium is released into the electrolyte by discharging. will be possible. However, the negative electrode material in the embodiments of the present invention is an alloy that is not alloyed with lithium.

For example, when using an alloy consisting of 70% bismuth and 30% tin by weight, the charge/discharge reaction is expressed as (B
i(70-5n(J)Lix indicates bismuth, tin, lithium alloy produced by charging, and the negative electrode material defined in the present invention is BiQ'Q-3n(
7).

In addition, as for the range of charging and discharging, it is not necessary to discharge until lithium is completely exhausted from the negative electrode as in equation (1), but it is necessary to change the amount of lithium occluded in the negative electrode as in equation (2). It is obvious that this is where charging and discharging can occur.

The inventors have developed a high-performance battery using an alloy consisting of at least two metals selected from the group of bismuth, tin, cadmium, and lead as a negative electrode material, and charging in a non-aqueous electrolyte containing alkali metal ions. Even when charged at a high current efficiency, alkali metals are occluded in the negative electrode material without precipitation of alkali metals, and when further discharged, the occluded alkali metals are released into the electrolyte as alkali metal ions with high current efficiency. I discovered that. It was also found that the negative electrode material did not become finely pulverized even after repeated charging and discharging, and exhibited good negative electrode characteristics of a non-aqueous electrolyte secondary battery.

When comparing an alloy of bismuth, cadmium, tin, and lead as a negative electrode material with these metals alone, the alloy showed better negative electrode characteristics. When viewed microscopically, most alloys consist of many phases such as various metal components and intermetallic compounds.
It's not uniform.

This is thought to be because alkali metals such as lithium absorbed by charging diffuse at a high rate along the interface between phases in the alloy.

By adding indium, carnoum, silver, mercury, antimony, and zinc to an alloy consisting of metals such as bismuth, tin, lead, and cadmium, it is possible to improve the negative electrode material by increasing the amount of charge and discharging electricity. started to show performance.

A cell shown in FIG. 1, a specific example of which is shown below, was constructed and the characteristics of the negative electrode of a non-aqueous electrolyte secondary battery made of various metals and alloys were investigated.

In Figure 1, A is a test electrode made of the two metal alloys studied, B is
C is a positive electrode made of Tl52, and C is a lithium plate as a reference electrode. Lead EA for each electrode.

Nickel wires were used for EB and EC. As shown in FIG. 2, the test electrode A was made of a metal or alloy DK of 1 ring x 1 cm thick and a nickel ribbon EA attached as a lead.

As the electrolyte F, PC in which 1 mol/l of L i C (J O4 was dissolved) was used.The liquid tank H of the test electrode A and the liquid tank G of the reference electrode C are connected by a communication pipe. .To measure the characteristics of metals and alloys as negative electrodes for non-aqueous electrolyte secondary batteries.
The potential of test electrode A is Om with respect to lithium reference electrode C.
The battery was charged toward the cathode with a constant current of 5 mA until the voltage reached V. Under these conditions, lithium does not precipitate on test electrode A but enters the alloy.

After the potential of test electrode A reaches Om V, 1. The battery was discharged toward the anode at a constant current of 5 mA until it became ○■, and then charging and discharging were repeated under the same conditions. The table shows the amount of electricity charged, the amount of electricity discharged in the first cycle and the 10th cycle of the alloy metal used for test electrode A,
The efficiency is the amount of discharged electricity divided by the amount of charged electricity, and the cycle characteristic is the amount of electricity discharged in the 10th cycle divided by the amount of electricity discharged in the first cycle. It can be said that the negative electrode has good values for charging amount of electricity, discharging amount of electricity, efficiency, and cycle characteristics. Further, the charging curve and the discharging curve at the 10th cycle of test electrode A, which are indicated by symbols in the table, are shown in FIG. 3 and FIG. 4, respectively.

(Left below) Based on the above results, compared to the conventionally used aluminum, lead, silver, and mercury, we selected bismuth, cadmium, tin, and lead as negative electrode materials for nonaqueous electrolyte secondary batteries. By using an alloy consisting of at least two metals, or an alloy in which at least one of indium, calcium, mercury, antimony, and zinc is added to this alloy as the negative electrode material, a cycle with a larger amount of charge and discharge electricity can be achieved. A secondary battery with good characteristics can be obtained.

The composition of the alloy used for the negative electrode material was studied by changing the composition of a bismuth cadmium alloy and a lead-tin alloy. The test method is the same as in the examples. 10 in Figures 5 and 6.
The amount of electricity discharged during the cycle was plotted against the composition.

From this, it was found that when the weight percentages of the constituent metals are approximately equal in terms of alloy composition, the performance as a negative electrode is the best, especially in terms of the amount of charge and discharge electricity.

In an alloy consisting of three metals, bismuth, tin, cadmium, and lead, the amount of electricity charged and discharged becomes large when the weight percentages of the two components with large amounts are approximately equal, and when the weight percentages of the three components are approximately equal, It turned out to be the best.

The small amount of charge and discharge electricity when mercury is used as the negative electrode material in the conventional example may be related to the fact that the sodium content in the sodium amalgam in mercury salt electrolysis is only about 0.2%.

In addition, in the above-mentioned example, an example was shown in which lithium was inserted into and released from the negative electrode material. It is also possible to construct a negative electrode that intercalates and desorbs alkali metals such as sodium and potassium in addition to lithium.

In addition, as an electrolyte, not only PC in which lClO4 is dissolved as shown in the example, but also solid electrolytes such as L 13N (lithium nitride) and LiI (lithium iodide) can be used instead of conventional aluminum or lead.

Bismuth and cadmium of the present invention compared to mercury and silver.

An alloy consisting of tin and lead showed excellent properties as a negative electrode.

Effects of the Invention As shown above, by using an alloy consisting of two or more metals selected from the group of bismuth, cadmium, tin, and lead as the negative electrode material, a large amount of charge and discharge electricity and good cycle characteristics can be achieved. A highly reliable non-aqueous electrolyte battery with a long charge/discharge life can be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the cell used to study negative electrode characteristics, Figure 2 is a side view of the test tank, Figures 3 and 4 are charging and discharging curves, respectively, and Figures 5 and 6. FIG. 1 shows the relationship between alloy composition and amount of discharged electricity. A...Test electrode, B...Positive electrode, C...---
- Reference electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Figure 04 B /2 /l 2/Figure 4 Patent Application No. 36879 2 Name of the invention Non-aqueous electrolyte secondary battery 3 Person making the amendment 4 Relationship with the company Patent issued
Appointment location Oaza Mon'JA1006, Kadoma City, Osaka Prefecture
Address name (582) Matsushita Electric Industrial Co., Ltd. 2/6
Toshihiko Yamashita 4 Agent
571 Address: 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. Subject 6: Contents of the amendment (1) Page 13 of the Specification 1 will be corrected as shown in the attached sheet. (Leap Figure 6 of the drawing is corrected as shown in the attached sheet. 5 Figure 9 Weight 71.-Y, F''

Claims (2)

[Claims] (1) Sn and Bi have the function of storing alkali metal ions in the electrolyte during charging and releasing the metal ions into the electrolyte during discharging, and are used as negative electrode materials. Non-aqueous electrolysis characterized by using an alloy consisting of at least two metals selected from the group Pb and Cd0. Secondary battery. (2) In, Ca, Hg, Sb, Zn,
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein at least one metal selected from Ag is added to the negative electrode material.