JPS60131776A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase energy density of a negative electrode for a secondary battery and improve charge-discharge performance by finely crushing negative electrode material comprising a metal which can absorb and release alkali metal ion, and kneading it with polytetrafluoroethylene resin. CONSTITUTION:An appropriate amount of polytetrafluoroethylene resin is added to fine powder of a metal such as Al or Sn which can absorb and release alkali metal ion according to charge-discharge of a battery, and they are kneaded and rolled with a roller to form a negative electrode. Since the material which can make a absorb and release reaction is dispersed in the polytetrafluoroethylene fibers, formation of fine powder caused by repeating of charge-discharge and hardening of negative electrode caused by absorption of alkali metal can be prevented. By using this negative electrode, reliability of a non-aqueous electrolyte secondary battery is increased.

Description

[Detailed description of the invention] industrial use The present invention 9 relates to a non-aqueous electrolyte secondary battery.

The configuration of the conventional example and its 9 problems.Currently, a non-small electrolyte secondary wire using an alkali metal such as a metal as a negative electrode is, for example,
Various compounds such as titanium disulfide (TiS2) were used as the positive electrode active material, and the electrolyte was 1, and lithium perchlorate (Lick4) was dissolved in an organic solvent such as propylev carbonate (hereinafter abbreviated as PC). Batteries using organic electrolytes are being actively developed. 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 cycles (cycles) is short, and the charging and discharging efficiency is low especially when charging and discharging the negative electrode side due to the formation of dendrites.

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 Li, or an additive to prevent the generation of dendrites is added to the electrolyte. However, these methods have not been effective enough to completely solve the above problems.

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, it is possible to form a homogeneous alloy, but the uniformity disappears when charging and discharging are repeated, and when the lithium content increases in particular, 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 the case of porcelain, it is said that there is no disintegration like in alloys 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, refinement due to charging and discharging is gradually accelerated, resulting in a rapid decrease in cycle life. In addition, there is a modification @ using a lithium-mercury alloy (Japanese Unexamined Patent Publication No. 57-98978), and a modification using a lithium-lead alloy (Japanese Unexamined Patent Publication No. 57-98978).
141869). However, in the case of a lithium-mercury alloy, the negative electrode becomes liquid mercury due to discharge, which poses problems in handling as an electrode plate. In addition, in the case of lithium-lead alloy, the fineness due to charging and discharging of the electrode is higher than that of silver solid solution, so the amount of lead in the alloy is reduced to 80 wt.
It is said that it is desirable to reduce the energy density to about 10%, but this makes it impossible to realize a high energy density battery.

As described above, it has been desired to develop an excellent negative electrode that has a large amount of alkali metal occlusion, a negative electrode material that has a high desorption and occlusion rate, and that has a stable electrode shape even after repeated charging and discharging. .

Furthermore, alloy materials made of Sn, Bi, Cd, Pb, etc. have been proposed as negative electrode materials. The characteristics of these materials are that they have high energy density and do not become pulverized by repeated charging and discharging.

However, although these alloy materials do not undergo fine powdering,
In the state where lithium is occluded, it is extremely hard and has poor workability, so it has the disadvantage that the only way to do so is to occlude lithium after constructing the battery.

Purpose of the Invention The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery, and an object of the present invention is to provide a negative electrode for a battery that can be charged and discharged with high energy density, excellent charging and discharging characteristics, and reliability. . □ Structure of the Invention The present invention relates to a negative electrode in which a metal or an alloy having the ability to electrochemically absorb or release an alkali metal is used as a negative electrode material. That is, in order to add mechanical strength to a negative electrode made of a metal or alloy that has the ability to absorb and release alkali metals, the negative electrode material is pulverized, kneaded with tetrafluoroethylene resin, and rolled. This is the negative electrode.

This is intended to prevent pulverization during charging and discharging and hardening of the negative electrode itself after absorbing alkaline metal.

As an example related to the present invention, the following study was conducted using Al and Sn which are alloyed with Li.

Commercially available powders were used for Al and Sn, and commercially available polyfine powder was used for the tetrafluoroethylene resin.

First, for Al and Sn powders respectively.

Tetrafluoroethylene resin was added and kneaded in an amount of 10 wt % for Sn and 5 wt % for Sn. When kneaded in this way, it becomes a soft rubber clay-like mass, and by rolling this with a roller 2-roller, it is filled and bound to 5 wt%. This is because the conductivity of the film itself decreases significantly if the temperature is higher than that. Next, as shown in Fig. 1, a prototype film-shaped negative electrode material 1 with a thickness of about 0.2 m was crimped onto the N1 expansion band metal 2, cut into 10x10- pieces, and made of Ni.
A test electrode was attached with ribbon glue 3. In addition, for comparison, metal-only electrode plates for Meni, A/Sn and Sn were each trial-produced by pressing powder to the same dimensions as the test electrodes shown in FIG. 1.

In order to charge and discharge the test electrodes as described above, the second
A test electrode 6 and a lithium electrode 7 were placed in an H-shaped test cell 6 partitioned by a glass filter 4 as shown in the figure, and 1 mA was applied in a propylene carbonate electrolyte 8 in which 1M lithium perchlorine (LiClO4') was dissolved. Constant current charging and discharging was performed.

As a result, all of the test electrodes began to change color as Li ions were absorbed and gradually expanded.

In particular, for test electrodes made only of single metals such as A4 and Sn, when a certain amount of occlusion is exceeded, the electrode plate itself collapses.
So-called pulverization occurred.

This is a diagram showing the change in the potential of the test electrode (based on the potential of metal Li) due to the occlusion of aluminum.
With the Sn metal electrode, the potential began to become unstable after the storage capacity exceeded 100 mAh, and around this time the electrode plate also began to collapse. Although expansion occurred, the plate itself did not collapse. However, the electrical capacity was slightly lower due to the resin and polarization. In particular, since AI powder requires more tetrafluoroethylene vocal fat than Sn powder, the amount of Li that it can store was smaller than that of Sn electrode plates.

For example, even when lithium ions are occluded under the above-mentioned occluded conditions (1 mA constant current) and a current is passed until the potential reaches 0, the result (a in Fig. 4) remains unchanged.
), it only expands and does not collapse, but
In the case of single metal electrodes, both AI and Sn collapsed and fell off as shown in FIG. 4(b).

The above is just an attempt at the initial occlusion of Li ions on the test electrode, but assuming actual charging and discharging,
Using the test cell shown in FIG. 2, the potential of the test electrode was varied from 0v to 1.0v with respect to the Li reference electrode. Charging and discharging were performed at 1 mA in the range of ov. However, regarding the metal electrode, it was known that charging (occlusion) to 0V during the occlusion test would cause the electrode plate to collapse, so charging was stopped before the potential became unstable.

However, when charging and discharging are actually attempted, the metal electrodes gradually collapse and the capacity decreases.In the case of AI electrodes, they all fall off in the 4th to 7th cycles, and in the case of Sn electrodes, they fall off by the 10th to 16th cycles. have all fallen off. Some of the debris generated by this electrode plate falling off remained at the bottom of the cell, while others were floating in the electrolyte as fine powder. child.

The substance generated by the falling off is an active substance called Li-Al1 or Li-Sn alloy, and if this drifts and comes into contact with the positive electrode, it will cause what is called an internal short circuit of the battery. Therefore, even though the test electrode of the present invention, which was prototyped using a single metal electrode, was subjected to the above charge/discharge cycles up to 100 cycles, the electrode plate did not collapse at all, and although the capacitance was slightly small, as shown in Figure 6. As shown, the charge/discharge characteristics from the initial stage to the 100th cycle were very stable. In addition, in this test, the Li electrode of the -C1 counter electrode was stagnant, causing significant dendrite formation, and the electrode plate and electrolyte on the Li electrode side of the H type cell were replaced periodically (every 6 cycles).

Next, an example in which the present invention is applied to an alloy electrode instead of a simple metal will be shown below.

Among the alloy electrodes that have recently been reported as excellent negative electrode materials, a Sn--Cd alloy containing 85% Sn and 15% Cd was investigated. Using this alloy, for example, a test electrode as shown in FIG. 1 was prototyped, and it was completely free of Li, unlike the electrodes made of Sn or Al as single metals. This is the superiority of this type of alloy, which has never existed before. However, in this type of alloy electrode, as Li ions are absorbed,
The alloy itself does not lose its inherent malleability, and the electrode plate becomes hard and brittle. For example, if you occlude Li ions in an alloy plate and then hit it with a spray gun, the plate that would not have even cracked if Li was not occluded will be shattered into pieces.

This hardening of the electrode does not affect the performance of the battery when it is normally used, but it may also cause the battery to become hard, for example, if the battery is subjected to an external impact.
This is still undesirable from the standpoint of safety or critical reliability. Therefore, we prototyped a Sn-type battery. In addition, this study used fluorinated graphite for primary batteries as the positive electrode because it was a study of reliability. As shown in FIG. 6, the button-type battery for consideration consists of a positive electrode 13 made of fluorinated graphite and a test electrode 14 of the present invention.
and a polypropylene separator 16, and sealed with a gasket 16, a sealing plate 17, and a battery case 18 together with a propylene carbonate electrolyte 19 in which 1 M L 1 Cl O 4 was dissolved to obtain a completed battery. In addition, since the test electrode does not contain Li, which becomes an active material, as shown in FIG.
is pressed onto the sealing plate 21 in advance, and brought into contact with metallic lithium 23 in an electrolyte 22 containing Li ions.
It absorbed ions.

The discharge characteristic curve 26 of the 2 mA cell of the button type battery prototyped in this way shows that the polarization is slightly large and the discharge capacity is
(1.5V termination) was also small. However, the discharge characteristics of all alloy-only batteries are not necessarily equal to curve 2.4 in Figure 8.
However, at a ratio of about 3 ol, it exhibited abnormal characteristics as represented by several curves 26 indicated by broken lines in FIG. When they disassembled the defective battery that exhibited abnormal discharge, they found that the alloy electrode had cracked, and the fine pieces had been carried to the positive electrode. An investigation revealed that the cause of this failure was that the pressure applied during the crimping process broke the test electrode. Therefore, after making a prototype battery, we conducted a drop impact test (dropping it onto a steel plate from a height of 1 to 11 mm) using only alloy electrodes, and found that the failure rate due to sealing alone was 30%. However, when a drop test was added, the defective rate rose to 76 inches. As mentioned above, whether the electrode plate made only of alloy is superior in terms of characteristics or not, all of the prototype batteries showed discharge curve 2 in Figure 8.
4, and no defects occurred even when a drop test was conducted. As described above, from the viewpoint of plate strength, a flexible plate like the negative electrode of the present invention is desirable.

There is still a problem in battery manufacturing, as the alloy electrode becomes hard as it absorbs Li, so there is the inconvenience that Li must be absorbed after the battery is constructed. Since it is a flexible material similar to rubber clay, it is highly workable and the above-mentioned inconvenience could be solved.

It is known that in alkaline storage batteries using a zinc negative electrode, powdered zinc is bound with a resin to form an electrode plate. The purpose in this case was to increase the surface area of zinc to enable high rate charging and discharging, and to reduce the occurrence of dendrites by taking advantage of the fact that the true area is significantly larger than the apparent area. However, when deeply charged and discharged,
Since most of the negative electrode zinc was dissolved, only the resin remained on the negative electrode, and during charging, the zinc was not deposited uniformly and the formation of dendrites was noticeable. However, in the present invention, since lithium intercalation and desorption are utilized, even if deep charging and discharging are performed, only the amount of lithium intercalated in the negative electrode changes. The amount does not change, and charging and discharging always proceed uniformly on the negative electrode surface, and dendrites do not occur. Therefore, the concept of zinc electrodes cannot be applied to the electrodes of the present invention.

Effects of the Invention As described above, the present invention is not only capable of providing a battery with high energy density and particularly excellent reliability, but also significantly improves workability in manufacturing.

[Brief explanation of drawings]

Fig. 1 is an external view of a test electrode according to an embodiment of the present invention, Fig. 2 is a configuration diagram of the same H-type test cell, Fig. 3 is a potential change characteristic diagram during charging (occlusion) of the test electrode, FIG. 4 is a diagram showing the state of the test electrode after Li occlusion, FIG. 5 is a charge-discharge curve of the negative electrode in an embodiment of the present invention, and FIG. 6 is a cross-sectional view of a coin-type battery in an embodiment of the present invention. FIG. 7 is a diagram showing how Li is absorbed into the negative electrode of the same coin-type battery, and FIG. 8 is a discharge curve of the same coin-type battery. 1...Negative electrode material, 2...Ni extract band metal, 3...Ni ribbon lead, 4...
...Glass filter, 6...Sample cell,
6... Test electrode, 7... Lithium electrode, 8
・・・・・・Propylene carbonate electrolyte, 9・・・・・・A
116...Separator, 16...Gasket, 17°21...Sealing plate, 18...
...Battery case, 19.22... Electrolyte, 23
...Metallic lithium.

Claims (4)

[Claims] (1) The components are a positive electrode, an electrolyte containing alkali metal ion deprivation, and a negative electrode whose negative electrode material is a metal or alloy that absorbs or releases alkaline earth metal ions during charging and discharging. A non-aqueous electrolyte secondary battery comprising a self-negative electrode, the above-mentioned pulverized negative electrode material, ethylene tetrafluoride, and a carbonate resin. (2) The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative material is at least one metal selected from Sn, Al, Mq, Pb, and In. (3) Negative electrode materials include Sn, Bi, Pb, Cd1. In,
Sb. The non-aqueous electrolyte secondary battery according to claim 1, characterized in that it is an alloy consisting of at least two or more metal elements selected from Zn and Ag. (4) The nonaqueous electrolyte secondary battery according to claim 1, 2, or 3, wherein the alkali metal is lithium.