JPH0412585B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to the improvement of negative electrodes for non-aqueous electrolyte secondary batteries, and as a result of this improvement, rechargeable batteries with high energy density, long charging/discharging life, and excellent safety and reliability. It provides: Conventional configurations and their problems Until now, non-aqueous electrolyte secondary batteries using alkali metals such as lithium and sodium as negative electrodes have
For example, various interlayer compounds such as titanium disulfide (TiS ₂ ) are used as the positive electrode active material, and propylene carbonate (hereinafter abbreviated as PC) is used as the electrolyte.
Lithium perchlorate (LiClO ₄ ) in organic solvents such as
The development of batteries using organic electrolytes dissolved in such materials has been actively pursued. The characteristics of this secondary battery are:
By using lithium for the negative electrode, the battery voltage increases, resulting in a secondary battery with high energy density. 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. The cause of this is
This is largely due to the deterioration of the lithium negative electrode. That is, current lithium negative electrodes are mainly made by pressing a plate-shaped metallic lithium onto a screen-shaped current collector such as nickel, but the metallic lithium dissolves in the electrolyte as lithium ions during discharge. However, it is difficult to charge this and deposit it on the plate-shaped lithium as before discharging.
Phenomena occur such as dendrite-like (dendritic) lithium is generated and breaks off from the base and falls off, or small spherical (moss-like) lithium deposits are detached from the current collector. 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 functionality. 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. That is, regarding the current collector material,
It is effective for lithium 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. 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. For example,
Lithium-aluminum alloys are well known. 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. 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.
To prevent this, the use of porous materials is recommended. Therefore, charging efficiency at large currents is poor, and in alloys with a large amount of lithium, micronization is gradually accelerated by charging and discharging, resulting in a rapid decrease in cycle life. In addition, there are ideas using a lithium-mercury alloy (Japanese Patent Laid-Open No. 57-98978) and a idea using a lithium-lead alloy (Japanese Patent Laid-Open No. 57-141869). However, in the case of a lithium-mercury alloy, the negative electrode becomes liquid particle mercury due to discharge and no longer maintains its electrode shape.
In addition, in the case of lithium-lead alloys, the fineness due to charging and discharging of the electrode is greater than that of silver solid solution, and therefore it is said that it is desirable to keep the amount of lead in the alloy at around 80%. High energy density batteries cannot be realized. 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 negative electrode material that has a large amount of alkali metal occlusion and a high desorption and occlusion rate. OBJECTS OF THE INVENTION The present invention provides a non-aqueous electrolyte secondary battery that exhibits good characteristics such as a large charge/discharge amount 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 bismuth or an alloy containing bismuth 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 by discharging. It releases lithium ions into the electrolyte. Description of Examples As described above, in the secondary battery of the present invention, lithium is occluded in the negative electrode material alloy by charging,
Since lithium ions are released into the electrolyte by discharging, an alloy of bismuth and lithium or an alloy of bismuth alloy and lithium is formed by charging. However, the negative electrode material described in the present invention refers to bismuth metal or bismuth alloy before forming an alloy with lithium. For example, 70% bismuth and 30% by weight
The charge-discharge reaction when using an alloy made of tin is (1)
It becomes like the expression. Bi(70)−Sn(30)+xLi ⁺ +xe ^-Charge ―→ ←― Discharge [Bi(70)−Sn(30)]Li _x ……(1) In the formula, [Bi(70)−Sn(30) ]Li _x indicates bismuth, tin, and lithium alloy produced by charging, and the negative electrode material defined in the present invention is
Bi(70)−Sn(30). In addition, as for the range of charging and discharging, it is not necessary to discharge until lithium completely disappears 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 goes without saying that it can be charged and discharged. [Bi(70)−Sn(30)]Li _x +yLi ⁺ +ye ^-Charge ―→ ←― Discharge[Bi(70)−Sn(30)]Li _x+y ...(2) Also in equation (2) Negative electrode material is Bi(70)-Sn
It is obvious that (30). Furthermore, an alloy whose main component is bismuth is an alloy in which the heaviest metal in the alloy is bismuth. The inventors have discovered that by using bismuth or an alloy mainly composed of bismuth 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 also 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 bismuth metal and an alloy mainly composed of bismuth as negative electrode materials, the alloy showed better negative electrode characteristics. Many alloys made by adding lead, cadmium, tin, indium, etc. as other components to the alloy whose main component is bismuth, when viewed microscopically, contain many components such as each metal component and intermetallic compounds. 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 with bismuth as the main component 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 FIG. 1, A is a test electrode made of the studied metal or alloy, B is a positive electrode made of _TiS2 , and C is a lithium plate as a reference electrode. Lead E _A of each electrode,
Nickel wires were used for E _B and E _C. As shown in Figure 2, the test electrode A is a metal or alloy D with a size of 1 cm x 1 cm and a thickness of 1 mm, with a nickel ribbon as a lead.
I installed E _A. Electrolyte F contains 1 mol/l
PC in which LiClO ₄ 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 I. In order to measure the characteristics of a metal or alloy nonaqueous electrolyte secondary battery as a negative electrode, test electrode A was charged in the cathode direction with a constant current of 10 mA until the potential of test electrode A became 0 mV with respect to lithium reference electrode C. Under these conditions, lithium does not precipitate on the test electrode but enters the alloy. After the potential of test electrode A reaches 0mV,
It was discharged toward the anode at a constant current of 10 mA until the voltage reached 1.0 V with respect to reference electrode C, and then charging and discharging were repeated under the same conditions. The table shows the amount of electricity charged and the amount of electricity discharged in the first and tenth cycles of the alloy and metal used in test electrode A, the efficiency calculated by dividing the amount of electricity discharged by the amount of electricity charged, and the cycle characteristics of the It shows the amount of electricity discharged in 10 cycles divided by the amount of electricity discharged in the first cycle. It can be said that the larger the numerical values of the amount of charging electricity, the amount of discharging electricity, the efficiency, and the cycle characteristics are, the better the negative electrode is. 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.

【table】

[Table] From the above results, bismuth or an alloy mainly composed of bismuth is better as a negative electrode material for nonaqueous electrolyte secondary batteries than the conventionally used aluminum, lead, silver, and mercury. I understood. Furthermore, when comparing bismuth and bismuth alloy, the alloy shows better properties. The table also shows the negative electrode properties of the other metals used to make the bismuth alloy. This shows that the performance was better when using an alloy than when using individual metals of each component. Furthermore, as shown in the table, as shown in the bismuth-cadmium alloy, there was a tendency for the performance to improve as the amount of other components increased. When mercury is used as the negative electrode material, the small amount of charge and discharge electricity may be related to the fact that the sodium content of 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. Furthermore, as an electrolyte, not only PC in which LiClO ₄ is dissolved as shown in the example, but also Li ₃ N (lithium nitride) can be used.
Even when a solid electrolyte such as LiI (lithium iodide) is used, it is better to use the bismuth or bismuth-based alloy of the present invention as a negative electrode material than conventional aluminum, lead, silver, or mercury. Characteristics were obtained. Effects of the Invention As explained above, by using bismuth or an alloy containing bismuth as the main component of the present invention as a negative electrode material, it is possible to achieve a high charge/discharge amount, good cycle characteristics, and a long charge/discharge life. A non-aqueous electrolyte battery with excellent properties can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram of the cell used for examining the negative electrode characteristics, Figure 2 is a side view of the test electrode, Figures 3 and 4.
The figures are a charging curve diagram and a discharging curve diagram, respectively. A...test electrode, B...positive electrode, C...verification electrode.

Claims (1)

[Claims] 1. It has the function of occluding alkali metal ions in the electrolyte during charging and releasing the metal ions into the electrolyte during discharging, and contains metal bismuth,
Alternatively, a non-aqueous electrolyte secondary battery characterized by using an alloy containing bismuth as a main component. 2. The non-aqueous electrolyte 2 according to claim 1, wherein the negative electrode material is an alloy containing bismuth as a main component, and at least one of cadmium, lead, tin, and indium is used as an additive component. Next battery.