JPS62283559A - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

PURPOSE:To obtain high capacity and long life by specifying particle sizes of cadmium and/or zinc in the alloy organization. CONSTITUTION:A negative alloy electrode is used, that the particle sizes of cadmium and/or zinc of the alloy electrode containing the cadmium and/or zinc as necessary components and besides containing at least one kind chosen from the group composed of lead, tin, indium and bithmus are made 5mum or smaller in the alloy organization. The cadmium or zinc, a metal component of the second group in the metal organization carries out a role like binder and the finer the metal disperses in the alloy organization the greater its effect becomes. Thereby, high capacity is obtainable and besides the cyle-life can be elongated.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to a non-aqueous electrolyte secondary battery using an alkali metal, particularly lithium, as a negative electrode active material.

BACKGROUND OF THE INVENTION Currently, non-aqueous electrolyte secondary batteries using an alkali metal such as lithium as a negative electrode active material are being actively developed.

However, it has not yet been put into practical use. The main reason for this is that the charging/discharging life is short and the charging/discharging efficiency is low. This is largely due to the negative electrode. This type of battery, which charges and discharges, uses metallic lithium as the negative electrode in the same way as used in negative batteries.
It is difficult to deposit lithium dissolved into the electrolyte by discharging into the original plate-like lithium by charging. For example, upon charging, lithium is irregularly precipitated in the form of dendrites, which may fall off the electrode plate or penetrate the separator and come into contact with the positive electrode, causing a short circuit.

This results in low charge/discharge efficiency and short lifespan. In order to improve this one drawback of lithium negative electrodes, various studies have been carried out in the past.

Among these methods, there is a method of using a certain type of metal or alloy as the negative electrode material, which has the function of occluding lithium ions in the electrolyte during charging to form an alloy with lithium, and releasing lithium as ions into the electrolyte during discharge. considered the most promising. This type of negative electrode material includes aluminum (U.S. Pat. No. 3,607,413), silver (Japanese Patent Application Laid-open No.
No. 386 U.S. Pat. No. 4,316,777, U.S. Pat. No. 4,33
0,601), lead (Japanese Unexamined Patent Publication No. 57-141869),
Tin, tin-lead alloy, etc. are known. These materials are
If the amount of lithium absorbed by charging is increased, the negative electrode material becomes pulverized, which has the disadvantage that the electrode cannot maintain its shape.

On the other hand, the alloy previously proposed by the present inventors, namely,
Domium (Cd) and/or zinc (Zn) are essential components, and in addition lead (Pd) and tin (Sn).

Alloys containing at least one selected from the group consisting of indium (In) and bismuth (Ei) have a relatively large lithium storage capacity and excellent charge/discharge reversibility, making them promising as rechargeable negative electrodes. It turned out to be. Hereinafter, the above alloy proposed by the present inventors will be referred to as a fusible alloy.

As the present inventors have already reported, the fusible metal is
It melts at a relatively low temperature, generally below 300°C.

When raw metals (usually powder or granules are used) in a predetermined ratio corresponding to the desired alloy composition are mixed and heated, they easily melt at 300'C or less, forming a molten alloy. Become. There are several methods of manufacturing alloy electrodes from molten alloy. For example, the molten alloy is naturally cooled to form an ingot, which is then rolled into an electrode plate. These methods include a method in which a shaped current collector is immersed and pulled up to deposit the alloy on the current collector, or a method in which molten alloy is poured into an electrode plate mold.

Problems to be Solved by the Invention The performance of this alloy electrode as a negative electrode is mainly determined by the component metals contained in the alloy and their composition ratios.

The component metals in the negative electrode have two different roles due to their roles.
It can be divided into two groups. One is the aforementioned lead (pb
), tin (Sn), indium (In), and bismuth (
These are metals that mainly contribute to occlusion and desorption of lithium (Li), and themselves serve as a matrix for occluding Li. The other one is the group (second group) consisting of the aforementioned cadmium (Cd) and zinc (Zn). It acts as a binder to maintain structural durability against repeated cycles. That is, the feature of the fusible metal negative electrode is that it utilizes the functions of the above two groups in combination. However, on the other hand, it was also found that they offset each other's roles.

For example, in the case of a Pb-Cd binary alloy, normally, as the content ratio of Pb in the first group increases, the Li occlusion-desorption capacity improves, but the durability against cycles decreases and the life span becomes short.

Furthermore, when the Cd content ratio of the second group increases, the durability against cycles improves and the life span becomes longer, but the Li occlusion-desorption capacity decreases. This is true not only for the binary alloy of Pb-Cd, but also for all combinations of the metals of the first group and the metals of the second group.

That is, by controlling the content ratio of the metal components of the first group and the metal components of the second group, it is possible to create a negative electrode oriented toward high capacity or long life, but this is not a means to improve both characteristics at the same time. .

Therefore, current technology cannot meet even higher performance requirements.

When making a negative electrode alloy containing metal components of the first group and metal components of the second group, mixing powder or granular metal raw materials and heating and melting them in an alumina crucible or stainless steel container will easily fuse and form an alloy. do.

An alloy electrode for a negative electrode has been manufactured by naturally cooling and solidifying this alloy.

However, as a result of further investigation by the present inventors, it was found that the morphology of the alloy structure changes depending on the cooling rate during solidification. Furthermore, as a result of examining the morphology of the alloy structure in the alloy electrode, as shown in Figure 6, metal grains of the second group (hatched areas in the figure) were found in the metals of the first group (white part in the figure) (A). It was found that the particles (part) and (b) had almost the same particle size and were uniformly dispersed, and that the cooling rate changed the particle size of the metal particles. Furthermore, as the cooling rate increased, the particle size of the metal particles became finer.

As a solution to the problem, we examined the negative electrode characteristics of alloy electrodes with the same composition with different metal grain sizes.We found that although the charge/discharge capacity remained the same, the smaller the grain size, the shorter the cycle life of the negative electrode. The effect was particularly great when the particle size of the metal particles was 6 μm or less.

Therefore, Cd and/or Zn are essential components, and P
An excellent non-aqueous electrolyte secondary can be obtained by using an alloy negative electrode containing at least one selected from the group consisting of B, Sn, In, and Bi, in which the grain size in the alloy structure of Cd and/or Zn is 6 μm or less. This is something that batteries can achieve.

Cd or Zn, which is the second group metal component in the working alloy structure, is
Originally, it plays the role of a binder. This provides structural durability against intercalation and desorption of Ll, and it is thought that the more finely these metals are dispersed in the alloy structure, the greater the effect. However, in the conventional alloy electrode, the dispersed metal particles were too large, as shown in FIG. 6, and it seems that the structural durability was insufficient.

Therefore, by finely dispersing the metal particles of the second group and enhancing the binding effect, a negative electrode with high capacity and excellent cycle life can be obtained.

Example Examples of the present invention will be shown below.

The composition of the fusible/alloy electrode is the above first group (Pb, Sn, In
or Bi) and the second group (Cd or Zn), for example, Pb-C
From two-component systems such as d and 5n-Cd, Pb-3n-I
Up to six component systems such as n-Bi-Cd-Zn can be adjusted. As a result of the study, it was found that the structure of the alloy usually has a structure in which the metal holes of the second group are dispersed in the form of particles in the metal of the first group, as shown in Figure 6, regardless of the amount of components. I found out that I have it. Therefore, as an example, an embodiment of a two-component system of Pb-Cd will be described. First, several Pb-Cd alloys were prepared by changing the content ratio of Pb-Cd.

A predetermined amount of granular PB (particle size 1 to 2 mm) and granular Cd (particle size 1
- 21a) were mixed, placed in a stainless steel container, and heated to fuse the two to form an alloy. The fully fused alloy was then poured into a preheated stainless steel plate mold, shaped, and cooled. Third
Figures A and B show the external appearance and cross-sectional view of a plate-type device for pouring and cooling the alloy. A refrigerant such as water is passed through the tank to cool it. Further, in order to measure temperature changes, a thermocouple was installed in the hole 2 provided near the recess 1. Conventional so-called natural cooling corresponds to the case where the above-mentioned refrigerant is not used, and when the cooling rate at that time was measured at room temperature, it was about 1o''C to 20'C/sec. First, an alloy plate with an area of 1 x 1 d and a weight of 0.1 g was prepared in the case of natural cooling.The alloy had a content ratio (weight ratio) of PB and CD of 90:10.
(8), ao:2omon).

7o:3o(q, so:4o(D), so:5o(E)
.

40:60 mouth, 30 near 01Q, 20:80 (c).

Nine types of 10:90 (I) were studied. When the alloy electrodes (I X 1 , J ) were made using 0.11 of the above various alloys, the thickness of each of them was about 0.1 m. In order to use these alloy electrodes for the charge/discharge test, as shown in Figure 4, the alloy electrode 4 was sandwiched between Ni expanded metals 3, crimped from both sides, and the outer periphery of the Ni expanded metal was spot welded. , a Ni IJ bond 6 lead was attached to serve as a current collector. This alloy negative electrode was charged and discharged in a glass cell shown in FIG.

In FIG. 5, an alloy negative electrode 6 and a metal Ll electrode 7 as a counter electrode are opposed to each other via a separator 8 of a glass filter, and together with a metal Ll electrode 9 as a reference electrode, 1 mol/2 of LLC1○ is placed in a glass cell 10. 4 was placed in an electrolytic solution 11 consisting of propylene carbonate dissolved therein. As a result of continuing charging and discharging using this cell, even if the capacity of the Lii of the electrode was increased in advance (more than 10 times the charging and discharging capacity of the alloy electrode), the capacity of the Lii was reduced due to the occurrence of punto-depletion etc. Lost with the cycle. Therefore, the test was conducted while periodically replacing the counter electrode and the electrolyte. Further, charging and discharging are performed at a constant current of 0.5 mA, and charging is performed at a constant current of 0.5 mA with respect to the metal Li reference electrode 9.
2■, a voltage control method in which the discharge is carried out to 0.6V with respect to the reference electrode, that is, 0.2V-o with respect to the reference electrode.
, eV was used.

Figure 1 shows natural cooling (in this case, the Cd particle size is approximately 20 μm).
Various Pb-Cd alloy electrodes (0,
11> is a diagram showing the relationship between the average charge/discharge capacity and cycle life (the number of cycles until the capacity deteriorates to 60% of the initial charge/discharge capacity). As can be seen from Figure 1, Pb
- In the Pb-Cd binary alloy with different Cd content ratios (A-I shown in the figure), the Pb content (
wt%) increased, the charge/discharge capacity improved, but the cycle life decreased.

Next, using the apparatus shown in FIG. 3, alloy electrodes were prepared in which the particle size of the Cd grains was changed depending on the cooling rate of the various Pb-Cd alloys mentioned above.
A charge/discharge test similar to that described above was conducted.

Cooling is carried out using PB in the recess 1 on the preheated electrode plate mold shown in Fig. 3.
A predetermined amount of a molten alloy was poured into the tube and the shape was adjusted, after which a refrigerant was poured into the tube.

Since the cooling rate depends on the heat capacity and flow rate of the refrigerant, it was adjusted by using refrigerants with different heat capacities, such as water, methanol, machine oil, etc., and changing the flow rate.

The particle size of Cd grains in the Pb-Cd alloy became smaller as the cooling rate increased, but it was hardly affected by the Pb-Cd content ratio. For example, among the various alloys mentioned above, Pb
An alloy electrode with the highest content of Pb:Cd=90:10,
Comparing the alloy structures of alloy electrodes with Pb:Cd=10:90, which has the highest Cd content, as shown in Figure 7, at the same cooling rate, the grain sizes of the Cd grains (shaded areas in the figure) are almost the same; The only difference was the relative amount of Cd grains. Therefore, the particle size of the Cd grains is 20 μm (corresponding to a naturally cooled alloy electrode), 16 μm, 10 μm, 7 μm, and 5 μm.
, 3 μm.

We investigated alloy electrodes of 1 μm and 0.5 μm.

Figure 2 is a diagram showing the relationship between average charge/discharge capacity and cycle life similar to the above, and a in the diagram shows the curve for natural cooling (Cd grain size is 20 μm) in Figure 2. corresponds to b
, C2d, e, f, q, and h have Cd grain sizes of 15 μm and 10 μm, respectively.

7μm, f5prn, 3prn, 1μm, 0.
It has an alloy electrode of 5 μm.

As is clear from Figure 2, the cycle life of alloy electrodes with smaller 06 grains tends to improve; The effect was significant.

In addition, the improvement in cycle life for the particle size of 06 grains is 6
The particle size was remarkable up to .mu.m, and below that, even if the particle size was lowered to, for example, 0.6 .mu.m, there was little improvement. Therefore, the particle size of the Cd grains should be reduced to at least 6 μm, preferably 6 μm to 0.6 μm.

Next, other alloy systems such as 5n-Cd, Pb-In-C
d.

As a result of similar studies on B1-Cd, etc.,
All alloy electrodes in the present invention are Cd.

It was found that there is an effect by lowering the particle size of the second group of metal components such as Zn. In both cases, it was found that when the particle size of the metal component of the second group was 5 μm or less, an excellent cycle life was obtained.

Effects of the Invention As described above, by using the negative electrode of the present invention, the cycle life of the negative electrode is improved, and a non-aqueous electrolyte secondary battery with high energy density and long life can be provided.

[Brief explanation of drawings]

1 and 2 are diagrams showing the relationship between average discharge capacity and cycle life of various alloy electrodes for comparing the effects of the present invention, and FIG. 3 is a schematic diagram of an apparatus for manufacturing alloy electrodes. Figure 4 is a schematic diagram showing the current collecting shape of the alloy electrode used in the example, Figure 6
The figure is a schematic diagram of the structure of a glass cell for conducting charge/discharge tests.
FIGS. 6 and 7 are schematic diagrams showing the state of dispersion of components in the fusible metal. Agent's name: Patent attorney Toshi Nakao, and 1 other person
! ! ]Wholesale? Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] Contains cadmium and/or zinc as an essential component, and further includes lead,
A nonaqueous electrolyte secondary battery comprising a negative electrode using an alloy containing at least one selected from the group consisting of tin, indium, and bismuth, wherein the essential components cadmium and/or zinc have an alloy structure. Among them, a non-aqueous electrolyte secondary battery characterized by particles having a particle size of 5 μm or less.