JPS62283560A - Manufacture of negative electrode for nonaqueous electrolyte secondary cell - Google Patents

Abstract

PURPOSE:To obtain high capacity and to prolong life by specifying the cooling rate in cooling process during the formation of an alloy electrode. CONSTITUTION:In the cooling process from molten alloy to an electrode plate, the cooling rate is made 100 deg.C/sec or above. Comparing alloy organization in case of natural cooling with that in case of cooling rate of 100 deg.C/sec, the metal particles of the second group are finer in the latter. Therefore, the structural durability of the alloy can be enhanced and high capacity and long life are obtainable by making fine the particles of the metal components of the second group, that is, metals carrying out a role like binder.

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, and particularly to a method for manufacturing its negative electrode.

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 primary 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 these drawbacks 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. Examples of this type of negative electrode material include aluminum (U.S. Pat.
No. 386, U.S. Pat. No. 4.316.777, U.S. Patent No. 4.3
30.601), lead (JP-A-57-141869)
,tin.

Tin-lead alloys are known. These materials have the disadvantage that when the amount of lithium absorbed increases through charging, the negative electrode material becomes pulverized, making it impossible to maintain the shape of the electric sign.

On the other hand, the alloy previously proposed by the present inventors has cadmium (Cd) and/or zinc (Zn) as essential components, and further contains lead (PB), tin (Sn), indium (In), and bismuth. It was found that alloys containing at least one selected from the group consisting of (Bi) have a relatively large lithium storage capacity and excellent charge/discharge reversibility, making them promising as rechargeable negative electrodes. . below,
The above alloy proposed by the present inventors is called a fusible alloy.

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

Then, 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. . There are several methods of manufacturing alloy electrodes from molten alloy. For example, the molten alloy is naturally cooled to form implant 1, which is then rolled to form 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 (Bi) (group 1), these are metals that mainly contribute to occlusion and desorption of lithium (Li), and they themselves contain Li. It is the mother body that absorbs energy. The other one is the aforementioned cadmium (Cd) and zinc (Z
n) (group 2), which hardly contribute to occlusion and release of Li, but mainly serve as a bond to maintain structural durability against repeated cycles of charging and discharging the negative electrode. It plays the role of adhesive. 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, Pb-
In the case of a Cd binary alloy, as the content ratio of Pb in the first group increases, the Li 2 storage-release capacity usually improves, but the durability against cycles decreases and the life span becomes short.

Furthermore, when the Ccl content ratio of the second group increases, the durability against cycles improves and the life span becomes longer, but the storage-release capacity of LL decreases. This is not limited to the two-component alloy of pb-cd.
This was true for all combinations of metals in the 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 facilitate the fusion. Alloy.

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

Means to Solve the Problem The inventors have further investigated and found that increasing the cooling rate during the cooling process from the molten alloy to the electrode plate changes the negative cycle life of the alloy. I found out that it does. Furthermore, by increasing the cooling rate, the cycle life can be improved without changing the Li storage and desorption capacity compared to alloys produced by conventional natural cooling (measured at 10°C to 20°C/sec). I found out. Particularly, in the above cooling step, when the cooling rate was set to 100°C/sec or more, the effect of improving the cycle life was remarkable. Therefore, an excellent nonaqueous electrolyte secondary battery can be achieved by using an alloy negative electrode manufactured at a cooling rate of 100° C./second or higher.

The reason why the alloy electrode of the present invention produced by cooling the molten alloy exhibits excellent charge/discharge reversibility and cycle life as a negative electrode for lithium secondary batteries is due to the fact that the alloy electrode of the present invention is produced by cooling the molten alloy.
This is because it has structural durability. This durability is due to the fact that Cd and Zn in the second group have a binding effect in the alloy. Therefore, as a result of examining the state of the alloy structure in the alloy electrode, the present inventors found that, as shown in FIG. It was found that the openings indicated by the second group of metal particles (shaded area in the figure) were uniformly dispersed.

However, when we compare the alloy structures in the case of natural cooling and in the case of cooling at a cooling rate of 100°C/sec, as shown in Figure 7, the latter has more metal grains in the second group (hatched area in the figure). His mouth was thin.

Furthermore, it was found that the metal particles in the second group became finer as the cooling rate was increased. Therefore, by using the manufacturing method of the present invention, the reason why the cycle life is improved is that the particles of this second group of metal components, that is, the metal that plays the role of a binder, become finer, and the structural durability of the alloy is improved. This is thought to be because of this.

Example Examples of the present invention will be shown below.

The composition of the fusible metal electrode is the above-mentioned first group (Pb, Sn.

In or Bi) and the second group (Cd or Zn), for example, Pb
-Cd, 5n-Cd and other two-component systems, Pb-
Up to six component systems such as 3n-In-Bi-Cd-Zn can be prepared. As a result of the study, it was found that regardless of the amount of components, the structure of the alloy usually has a structure in which the metal of the second group is dispersed in the form of particles in the metal of the first group, as shown in Figure 6. I understand. Therefore, as an example, Pb-Cd
Examples of the two-component system will be described below.

First, several Pb-Cd alloys were prepared by changing the content ratio of Pb-Cd. A predetermined amount of granular PB (particle size 1
~2IIs) and granular Cd (particle size 1 to 2 mm) were mixed, placed in a stainless steel container, and heated, and the two fused with each other to form an alloy. The fully fused alloy was then poured into a preheated stainless steel plate mold, shaped, and cooled. Figures 3A and 3B are external views and cross-sectional views of a plate-type device for pouring and cooling the alloy.
The pipe is shaped and cooled by flowing a refrigerant such as water into the pipe as shown by the arrow in the figure.

In addition, in order to measure temperature changes, a thermocouple is placed in the recess 1.
It was installed in hole 2 prepared near the. Conventional so-called natural cooling corresponds to the case where the above refrigerant is not used, and when the cooling rate at that time was measured at room temperature, it was about 10 ° C ~
The temperature was 20°C/sec. Using this electrode plate type, first, an alloy electrode plate having an area of 1×1 ad and a weight of 0.1y in the case of natural cooling was prepared. The alloy has a content ratio of PB and Cd of 90:10 (A).

8o: 20 (B), 70: 3o (C),
eo: 4o(Il19゜50:50(E), 4
o: 5o (F), 3o near o (Q.

Nine types were studied: 20:80 (H) and 10:90 (I). The above various alloys are used for 0.1y alloy electrode (1x
1 cal), the thickness was approximately 0.1111 in each case. In order to use these alloy electrodes for charge/discharge tests, 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 lead made of Ni ribbon 5 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, the alloy negative electrode 6 and the counter metal Li electrode 7 are opposed to each other with a separator 8 of a glass filter interposed therebetween.
A metal L1 serving as a reference electrode is placed in a glass cell 10 together with the electrode 9 in an electrolytic solution 11 made of globylene carbonate in which 1 mol/l of L I C1304 is dissolved. As a result of continued charging and discharging using this cell, even if the capacity of the opposite Li electrode 7 was increased in advance (more than 1° times the charge/discharge capacity of the alloy electrode), the capacity of the Li electrode remained low due to the formation of dendrites, etc. was lost with the cycle. Therefore, the test was conducted while periodically replacing the counter electrode and electrolyte. Also, charging and discharging is 0
．． Perform charging with a constant current of 5 mA, charge to 0.2 V with respect to metal L1 reference electrode 9, discharge with o,
Voltage control method up to sV, i.e. for reference pole,
A method of repeating cycles between 0.2V-o and eV was used.

Figure 1 shows the average charge/discharge capacity and cycle life (
It is a figure showing the relationship between the number of cycles until the capacity deteriorates to 50% of the initial charge/discharge capacity. As can be seen from Figure 1, the above Pb-C with different Pb-Cd content ratios
In the cl binary alloy (A, I), as 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 of the various Pb-Cd alloys described above with different cooling rates were prepared, and the same charge-discharge tests as above were conducted. Cooling was carried out by pouring an alloy prepared by mixing and melting a predetermined amount of PB and CD into the recess 1 on the preheated electrode plate mold shown in FIG. 3, shaping it, and then pouring a refrigerant into the tube. Since the cooling rate depends on the heat capacity and flow rate of the refrigerant, refrigerants with different heat capacities, such as water, methanol,
Adjustments were made by changing the flow rate using machine oil, etc. The cooling rate is natural cooling (10-20°C/sec (a)), 40"C/sec
sec, 60°C/sec, 80°C/sec, 1oo°c/sec.

120″C/sec, 150°C/sec, and 200°C/sec were investigated.

FIG. 2 is a diagram showing the relationship between average charge/discharge capacity and cycle life similar to the above, where a corresponds to the curve in the case of natural cooling in FIG. 1, and b, c, d.

The cooling rate of e+ ' + qr h+ is
4Q'C/sec, eo°c/sec, ao°c/sec, 100''
C/sec.

120″C/sec, 160°C/sec, and 2oo°C/sec alloy electrodes.As is clear from Figure 2, the cycle life of the alloy electrodes prepared by increasing the cooling rate is improved. In particular, alloys with large charge/discharge capacity (alloys with a high PB content ratio) had a remarkable effect.

In addition, the improvement in cycle life with respect to cooling rate is 100%
C/sec to 160 C/sec, and above that, even if the cooling rate was increased to, for example, 200 C/sec, there was little improvement. Therefore, the cooling rate should be increased to at least 100"C/sec, preferably more than 100"07 seconds.

Next, other alloy systems such as Sn-Cd, Pb-
As a result of conducting similar studies on In-Cd, B1-Cd, etc., it was found that the alloy electrodes of the present invention all have the effect of increasing the cooling rate. In both cases, it was found that manufacturing the alloy electrode at a cooling rate of 100° C./second or higher has a great effect.

Effects of the Invention When the production method of the present invention is used, the negative cycle life is improved, so non-aqueous electrolysis with high energy density and long life is possible.
We can provide the following batteries.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the relationship between the average discharge capacity and cycle life of various alloy electrodes for comparing the effects of the present invention;
Figure 3 is a schematic diagram of the apparatus for manufacturing alloy electrodes, Figure 4 is a diagram showing the current collecting shape of the alloy electrode used in the examples, and Figure 5 is a diagram of the glass cell used for charge/discharge tests. The structural diagrams, FIGS. 6 and 7, are schematic diagrams showing the state of dispersion of components in the fusible metal. Name of agent: Patent attorney Toshio Nakao and one other person Figure 5 Figure 6

Claims (1)

[Claims] A method for producing a non-aqueous electrolyte secondary battery, the components of which are a positive electrode, an alkali ion conductive electrolyte, and a negative electrode using an alloy that stores alkali metal ions during charging and releases the alkali metal ions during discharge. A method for producing a negative electrode for a nonaqueous electrolyte secondary battery, characterized in that in the step of cooling the molten alloy to form an alloy electrode, the cooling rate is 100° C./second or more.