JPS59163761A - 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-discharge 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 cadmium or an alloy principally consisting of cadmium as the negative electrode material. CONSTITUTION:Cadmium metal or an alloy principally consisting of cadmium 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. It is preferred that the above negative electrode material consisting of an alloy principally composed of cadmium contain at least one element chosen from among bismuth, lead, tin and indium as well.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to improvement of a negative electrode for non-aqueous electrolyte secondary batteries, and as a result of this improvement, it has a high energy density, a long charge/discharge life, safety, and reliability. This provides an excellent rechargeable battery.

Conventional configurations and their problems Up until now, non-aqueous electrolyte secondary batteries that use alkali metals such as lithium and strium as negative electrodes have used various interlayer compounds such as titanium disulfide (TiS2) as active electrodes. The development of batteries using an organic electrolyte prepared by dissolving lithium perchlorate (LiCd04) in an organic solvent such as propylene carbonate (hereinafter abbreviated as PC) has been actively pursued. 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 has not yet been put into 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 due to the deterioration of the lithium negative electrode, which is extremely thick (V/).

In other words, current lithium negative electrodes are mainly made by pressing a plate of metallic lithium onto a screen-shaped current collector such as nickel/L, but during discharge, metallic lithium is released as lithium ions in the electrolyte. dissolve. However, it is difficult to charge this and deposit it into the plate-shaped lithium that it was before discharge, and tendritic (dendritic) lithium may be generated that breaks off from the base and falls off, or small spherical (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. Unfortunately, the generated dendrite-like metallic lithium often penetrates the separator separating the positive and negative electrodes and contacts the positive electrode, causing a short circuit and causing the battery to lose its function.

Various attempts have been made to overcome 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, the current collector material is effective for lithium deposited directly on the current collector material, but if the charging (deposition) continues, lithium will be deposited on the precipitated lithium, and the effect of the current collector material will be reduced. Disappear. Furthermore, most additives are effective at the beginning of the charge/discharge 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 especially when the amount of lithium is increased, 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. 56-7386) In this case, it is said that there is no collapse like in alloys with aluminum, but the amount of lithium that alloys quickly enough is small, and metallic lithium remains unalloyed. Precipitation may occur, and the use of porous materials is recommended to prevent this.

Therefore, the charging efficiency of large currents is poor, and alloys with a large amount of lithium gradually accelerate their miniaturization through charging and discharging.
Cycle life decreases rapidly.

In addition, the idea of using a lithium-mercury alloy (Japanese Unexamined Patent Publication No. 5
7-98978), a device using lithium-lead alloy (
JP-A-57-141869). However, in the case of a lithium-mercury alloy, the negative electrode turns into liquid particles of mercury upon discharge, maintaining the electrode shape and providing strength. In the case of lithium-lead alloy, fine powdering by charging and discharging the electrode is
The amount of lead in the alloy was reduced to 8.
2) Although it is said that it is desirable to reduce the energy density to around 10%, this makes it impossible to realize a high energy density battery. As described above, it can be said that no practically satisfactory negative electrode for non-aqueous electrolyte secondary batteries has been found.

Therefore, as an excellent negative electrode, it is desirable to develop a negative electrode material that has a large amount of alkali metal occlusion and has a good desorption and occlusion rate.

OBJECTS OF THE INVENTION The present invention provides a non-aqueous electrolyte secondary battery exhibiting 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 cadmium or an alloy containing cadmium as a main component is used as a negative electrode material, and lithium is occluded in the metal or alloy used as the negative electrode material by charging, and lithium is occluded by discharging. It releases lithium ions into the electrolyte.

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 ions are released into the electrolyte by discharging. This results in the creation of an alloy, or an alloy of cadmium alloy and lithium. The negative electrode material described in the present invention refers to metal cadmium or cadmium alloy before forming an alloy with lithium.

For example, when an alloy consisting of 70% cadmium and 30% tin by weight is used, the charge/discharge reaction is expressed by equation (1).

In the formula, (Cd(7o)In(3o))Li represents a cadmium, tin, and lithium alloy produced by charging, and the negative electrode material defined in the present invention is c in the formula (1).
a(7o:)sn(3o).

In addition, regarding the range of charging and discharging, it is not necessary to discharge until the lithium is completely exhausted from the negative electrode as shown in equation (1), and it is not necessary to discharge until the lithium is completely exhausted from the negative electrode, as shown in equation (2). 70)-sn(so))Li,, sea-(2)
It goes without saying that charging and discharging can be done by changing the amount. Also in equation (2), the negative electrode material is Cd (70)
It is obvious that -3n(3o).

An alloy whose main component is cadmium is an alloy in which the heaviest metal in the alloy is cadmium.

The inventors have discovered that by using cadmium or an alloy mainly composed of cadmium as a negative electrode material and charging in a non-aqueous electrolyte containing alkali metal ions, no alkali metal precipitation occurs even during high-rate charging. It was discovered that alkali metals are occluded in the negative electrode material, and that when further discharge is performed, the occluded alkali metals are released into the electrolyte as alkali metal ions with high current efficiency. It was found that the negative electrode material did not become finely powdered even after repeated charging and discharging, and exhibited good negative electrode characteristics of a non-aqueous electrolyte secondary battery.

When comparing cadmium metal and an alloy mainly composed of cadmium as negative electrode materials, the alloy showed better negative electrode characteristics. Many alloys made by adding other ingredients such as lead, bismuth, tin, and indium to alloys containing cadmium as the main component can be seen microscopically to show that many of the metal components and intermetallic compounds are present. It consists of phases and is not uniform.

Alkali metals such as lithium absorbed by charging are thought to diffuse at a high rate along the interface between phases in the alloy, and when high-rate charging and discharging is performed, alloys mainly composed of cadmium It was better to use

The cell shown in FIG. 1 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 studied metal 1 alloy, 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 KCK. Test pole A is the second
As shown in the figure, a nickel ribbon E was used as a lead on a 1 mm thick ICInX11 metal or alloy.

I took it. The electrolyte contains 1 mol/l of Li(JO4
A PC solution containing the following 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 connecting electric wire. In order to measure the characteristics of gold 4 or alloy as a negative electrode of a non-aqueous electrolyte secondary battery, the potential of test electrode A is set to 0.0 m with respect to lithium reference electrode C.
The battery was charged in the direction of the cand with a constant current of 5 mA until the voltage reached V. Under these conditions, lithium does not precipitate on the test electrode but enters the alloy.

After the potential of test electrode A reached omv, it was discharged toward the anode at a constant current of 577 LA until it reached 10 V with respect to reference electrode C, and then charging and discharging were repeated under the same conditions. The table shows the alloy used for test electrode A.

The amount of charged electricity, the amount of discharged electricity in the 1st cycle and the 10th cycle of the metal, and the efficiency, which is the amount of discharged electricity divided by the amount of charged electricity, and the cycle characteristics, which is the amount of electricity discharged in the 10th cycle divided by the amount of electricity discharged in the 1st cycle. Shows the value divided by the amount of electricity. Charge electricity amount.

It can be said that the negative electrode has good values for the amount of discharged electricity, efficiency, and cycle characteristics. In addition, the charging curve at the 10th cycle of the test electrode indicated by the symbol in the table is shown in Figure 3, and the discharging curve is shown in Figure 4.
As shown in the figure.

(Left below) From the above results, aluminum has traditionally been used as a negative electrode material for non-aqueous electrolyte secondary batteries.

It has been found that cadmium or an alloy containing cadmium as a main component of the present invention is better than lead, silver, and mercury.

When comparing cadmium and cadmium alloys, the alloys show better properties. Table 1 also shows the negative test characteristics of Kinkuta, another component used to make the cadmium alloy. This shows that the performance was better when using the alloy than when each component was used alone. As shown in the table, as shown in the cadmium-lead alloy, there was a tendency for performance to improve as the amount of other components increased.

Note that when mercury is used as the negative electrode material, the amount of charge and discharge electricity is small because of the sodium in the sodium amalgam in mercury salt electrolysis. , which is related to the fact that it is only about 2%, is not surprising.

In the above embodiment, an example was shown in which lithium was inserted into and released from the negative electrode material. In addition to lithium, it also absorbs alkali metals such as sodium and potassium.

It is also possible to construct a negative electrode that allows emission to take place.

In addition, as an electrolyte, Li5N (lithium nitride), Li5N (lithium nitride), Li5N (lithium nitride), Li5N (lithium nitride), Li5N (lithium nitride), Li5N (lithium nitride), etc.
Conventional aluminum, lead, silver, even when using solid electrolytes such as I (lithium iodide).

An excellent negative electrode was obtained by using Bebismuth size or an alloy containing bismuth as the main component as the negative electrode material compared to mercury.

As described above, by using cadmium or an alloy containing cadmium as the main component as the negative electrode material, a highly reliable nonaqueous electrolyte with a large amount of charge and discharge, good cycle characteristics, and a long charge and discharge life can be achieved. You can get batteries.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a cell used for examining negative electrode characteristics, FIG. 2 is a side view of a test electrode, and FIGS. 3 and 4 are charging and discharging curve diagrams. A...Test electrode, B...Positive electrode, C...
...Reference electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure I I d , SJ /2
// 2σ no lyo 1-+ 80

Claims (2)

[Claims] (1) An alloy that has the function of storing alkali metal ions in the electrolyte during charging and releasing the above metal ions into the electrolyte during discharging, and whose main alloy is metal cadmium, sweet mushroom, or cadmium as the negative electrode paulownia material. A non-aqueous electrolyte secondary battery characterized by using. (2) The negative electrode material is an alloy containing cadmium as a main component, and at least one of bismuth, lead, tin, and indium is used as an additive component. Electrolyte secondary battery.