JPH0364869A - Secondary cell - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous electrolyte secondary cell having excellent performance by using a complex electrode of an alloy of sodium, bismouth, lead, cadmium, tin and a carbon material as well as a binder for a negative electrode. CONSTITUTION:A complex of an alloy consisting of sodium, bismouth, lead, cadmium, tin and a carbon material as well as a binder is used for a negative electrode. That is that activity of sodium is lowered by the sodium alloy to suppress side reaction to an electrolyte, while a conductive carbon material is dispersed in an electrode to impregnate the electrode with the electrolyte for suppressing a shape change and a breakdown of the electrode accompanying charge and discharge of with a binder. Various kinds of excellent performance such as high energy concentration, a long cycle life and a low self-discharge coefficient, etc., are obtained accordingly.

Description

[Detailed description of the invention]

[Industrial Application Field 1] The present invention relates to a secondary battery having high energy density, high battery voltage, low self-discharge, long cycle life, and good coulombic efficiency during charging and discharging.

[Prior art] The idea of a secondary battery using lithium metal, which is one of the alkali metals, as a negative electrode has been around for a long time.
Hughes, et al., Journal o
f PowerSources, 12. P.83
~144 (1984) contains a review. Among them, lithium metal is so active that it reacts with solvents, forms an insulating film, and causes dendrite growth, making it difficult to apply to negative electrodes for secondary batteries. As a countermeasure, attempts have been made to alloy lithium metal or composite it with conductive polymers, but these have been proposed by A. N. Dey, J.
+m. Soc,, 118. No, 1 mouth, P, 1547~
1549 (1971), JP-A No. 59-132576, JP-A No. 60-262351, JP-A No. 61-2454.
It is described in Publication No. 74, Publication No. 62-140358, etc. In addition, sodium-based negative electrodes are alloyed or composited with conductive polymers in the same way as above, but these are manufactured by Allied or AlliAlled-3.
U.S.P. 4,668,59 filed by i Inc.
6, 4, 753.858, etc. [Problems to be Solved by the Invention] By the way, as mentioned above, despite research in various fields, secondary batteries for room temperature operation using an alkali metal as the negative electrode are However, no battery has yet achieved a market comparable to that of general-purpose secondary batteries. However, some of them are extremely small capacity type (1mAh to 1OmAh).
) lithium-based secondary batteries are on the market. Additionally, Canada's MOLI ENERGY Lr [TED has commercialized a relatively high capacity (600+sAh) secondary battery using MoS for the positive electrode and Li foil for the negative electrode.
None of the charge/discharge cycle reversibility, high-speed charge/discharge characteristics, or overdischarge characteristics exceed those of nickel-cadmium secondary batteries of the same shape, and the energy density has only been improved, making it more versatile. poor. The main reason why this Li-based negative electrode is difficult to put into practical use is the short-circuit phenomenon caused by the reaction between lithium and the electrolyte and the resulting dendrite growth, as described above. By replacing lithium with sodium alloy, the electrode potential can be reduced to 0.
．． Since the voltage is shifted to the more noble side by about 2V to 0.4V, the reactivity with the electrolyte is somewhat alleviated, but it is not sufficient. As a result of intensive research to solve the above-mentioned problems, the present inventors have discovered an excellent combination of electrode constituent materials for the negative electrode. The present invention provides a secondary battery. [Means for Solving the Problems J] In order to solve the above-mentioned problems, the present inventor investigated and found that the negative electrode is a composite of an alloy consisting of sodium, bismuth, lead, cadmium, and tin, a carbon material, and a binder. ! The inventors have discovered that a nonaqueous electrolyte secondary battery with excellent performance can be obtained by using electrodes, and have completed the present invention. Moreover, at this time, a positive electrode containing sodium or cobalt oxide as a main component can be suitably used. The alloy is an alloy of sodium and a wood alloy,
The proportion of each element in the wood alloy is bismuth 30-50% by weight.
, lead IO to 50% by weight, cadmium 5 to 30% by weight, and tin 5 to 30% by weight.When the proportions of each element are outside the above ranges, the remarkable effects of the present invention are not achieved. Hard to obtain. However, simply using only a sodium alloy as an electrode does not improve the utilization rate and reversibility of the negative electrode, and it is necessary to use a composite electrode with a carbon material as in the present invention. Carbon black or graphite is suitable as the carbon material to be used. The above-mentioned carbon black includes thermal black, furnace black, acetylene black, etc., but any of them may be used and there is no particular restriction.Also, the graphite may be natural graphite or artificial graphite, or fibrous graphite synthesized by a vapor phase growth method. But that's fine. However, if the amount of carbon material is too large, the electrode capacity and density will be reduced. A suitable amount is 3% to 20% based on the weight of the negative electrode. Furthermore, to prevent the composite electrode from collapsing during use,
Although it is necessary to add a binder, it is necessary that it has no reactivity with the electrode or electrolyte, and is usually used by thoroughly dispersing polyethylene or polypropylene fibers or powder in the electrode and welding it by heating. In addition, examples of more effective binders for negative electrode materials include olefin copolymer rubbers such as ethylene-propylene rubber (EPR), ethylene-butene rubber (EBR), and ethylene-propylene-diene rubber (EPDM). EPDM is particularly preferred. If too much of this binder is used, the electrode performance will be impaired.The appropriate amount is 1% to 8% per negative electrode weight.
It is. When such a negative electrode is used, a suitable electrolytic solution is one in which a sodium salt is dissolved in a mixed solvent of 1,2-dimethoxyethane and an ether compound. When used in a mixed system with an ether-based compound, there are no particular restrictions on the type, but as a matter of course, those that strongly react with the electrode active material cannot be used. Non-aqueous solvents to be mixed include 5 such as ethoxy-methoxyethane, guiglyme, triglyme, tetraglyme, pentaglyme, tetrahydrofuran, 2-methyltetrahydrofurn, 1,4-3methyldioxolane,
Ether compounds such as dioxane, especially diglyme,
Triglyme and tetraglyme are preferred. Next, a positive electrode suitable for the battery of the present invention will be explained. The above-mentioned suitable positive electrode must have a voltage of at least 1.5 V or more with respect to the negative electrode used in the battery of the present invention, and must be capable of reversibly occluding and releasing sodium ions, and must be one that has an inorganic oxidation For example, Coma, M
Examples of inorganic chalcogenides include n0z, WO, Maxi, Mo03, V2O5, etc.
Examples of inorganic halides such as o5ss and N1PSes include RuC1z, RuBra, and Fe0C1. Among these, Coax and Moa have high electric capacity and density per weight and volume, and have good reversibility.
t, Mo03, and COO2 is particularly preferred. This Con It also works to suppress repulsion, and an increase in the amount of Na does not necessarily lengthen the C-axis of the host lattice, but only slightly lengthens the a-axis and b-axis. Therefore, the change in shape of sodium and cobalt oxides with CoO□ as hosts during charging and discharging is relatively small, and they are less prone to collapse than other inorganic substances. Furthermore, because sodium and cobalt oxides have high electronic conductivity, , almost no conductive aids are required. Therefore, sufficient performance can be exhibited as an electrode even if the amount of conductive additive is small or even if no conductive additive is used at all. [Function J] The reason why a composite of an alloy consisting of sodium, bismuth, lead, cadmium, and tin, a carbon material, and a binder is used for the negative electrode in the present invention is that the sodium alloy first lowers the activity of sodium and In addition to suppressing side reactions with the liquid, dispersing the conductive carbon material in the electrode allows the electrode to be impregnated with the electrolyte, further increasing the effective surface area, lowering the effective current density, and improving binding. This is to suppress changes in shape and collapse of the electrodes due to charging and discharging. The reason why the sodium alloy used in the above composite negative electrode is a multi-component alloy is that the dispersion of each element in the alloy leads to the dispersion of absorption and storage of alkali metal ions, and by becoming multi-component, the interaction of these metals is This is because it is thought that the interface between the two layers increases, making it possible to store more alkali metal ions. [Example J] Next, the present invention will be explained in detail with reference to an example. Example 1 The negative electrode has an atomic ratio of Bi, Cd, pb, and Sn of 0.5:0
．． After finely pulverizing an alloy with an atomic ratio of Na of 1:3.0 to a wood alloy of 125:0.25:0-125, premixed acetylene black and EPDM (binder ) was added in a weight ratio of 3:1 and mixed so that the Na alloy was 88% and the above mixture was 12% to form a negative electrode active material, with a diameter of 15 mm + and a thickness of 300 mm.
It was produced by pressure molding into a disc shape to a thickness of approximately μm. In addition, the positive electrode is made by heating and reacting NazOz and GO$04 in an oxygen atmosphere to synthesize Nao and ycoO*, which are then crushed, and then mixed with acetylene black and tetrafluoroethylene (binder), which have been mixed in advance. Add a mixture with a weight ratio of 3:l and mix so that Nao and tCOO* are 95% and the mixture is 5% to form a positive electrode active material.
It was prepared by pressure molding into a disc shape so that it had a thickness of about 1I and a thickness of about 400μ. The electrolyte was 1.2-dimethoxyethane with 1 part of NaPF5.
．． A solution dissolved so that the concentration was 0 mol/β was used. A polypropylene microporous film and a polypropylene nonwoven fabric are used as separators between the positive and negative electrodes.
A well-known coin-shaped cell as shown in FIG. 1 was assembled. The voltage of this battery immediately after assembly was 2.46V. This battery is discharged with a current of 2.0+iA and a battery voltage of 2.
Discharge until it reaches OV, then at the same current value the battery voltage reaches 3. When the discharge capacity and reversibility of this battery were investigated by charging it until it reached OV and then repeating discharging and charging, the maximum discharge capacity was 13.5wAh, and the maximum discharge capacity was 8.
The cycle life until it decreased to 0% was 640 times. Furthermore, when we assembled the exact same battery as above, left it in a charged state for one month at room temperature, and examined the self-discharge rate.
It was 4.8%. Further, when the positive and negative electrodes were short-circuited and left for 3 days, charging and discharging was attempted, and no abnormalities were observed, and the battery operated normally. Example 2 The negative electrode was made of a wood alloy in which the atomic ratio of Bi, Cd, PB, and Sn was 0.4:2 and 15:0.25:0.20, and Na was in the atomic ratio of 1:3.0. The same material as in Example 1 was used except that a certain alloy was used. The battery was a coin-shaped cell as shown in FIG. 1, and the same experiment as in Example 1 was conducted. As a result, the maximum discharge capacity was 13.11wAh, and the cycle life until the discharge capacity decreased to 80% of the maximum value was 6.
The self-discharge rate was 5.2%, and no abnormality was found even when an overdischarge test was conducted 64 times. Implementation W43 The positive electrode was made by mixing commercially available Mo5s, acetylene black, and polytetrafluoroethylene at a weight ratio of 80:15:5 and molded in the same manner as in Example 1, and the negative electrode was exactly the same as in Example 1. I used the one from In addition, the electrolytic solution was a mixed solvent of tetraglyme and 1,2-dimethoxyethane with a volume ratio of 1:4, and 1.1% NaPFa.
A solution dissolved so that the concentration was 0 mol/β was used. The battery was a coin-shaped cell as shown in FIG. 1, and the same experiment as in Example 1 was conducted. However, only the discharge end voltage is 1.5.
I lowered it to V. As a result, the maximum discharge capacity is 12.5mAh, tel
The cycle life until the capacity decreased to 80% of the maximum value of the electric furnace capacity was 670 cycles, the self-discharge rate was 6.3%, and no abnormality was observed even when an overdischarge test was performed. Example 4 The negative electrode has an atomic ratio of Bi, Cd, pb, and Sn of 0.4:0
．． The same material as in Example 1 was used except that an alloy in which the atomic ratio of Na was l:2.5 with respect to the wood alloy which was 125:0.25:0.125 was used. The battery was a coin-shaped cell as shown in FIG. 1, and the same experiment as in Example 1 was conducted. As a result, the maximum discharge capacity was 14.1 mAh, the cycle life was 595 times, the self-discharge rate was 4.7%, and no abnormality was observed even when an overdischarge test was performed. [Effects of the Invention] As described above, the secondary battery of the present invention has high energy density, long cycle life, low self-discharge rate, etc.
Since it has many excellent performances, it will greatly contribute to the field of using it as a power source.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a coin-shaped secondary battery used to examine battery performance in Examples. 1...:...Positive electrode. 2...Wire mesh for current collection, 3-...Polypropylene nonwoven fabric, 4...
- Polypropylene microporous film, 5... Insulating backing, 6... Negative electrode.

Claims (2)

[Claims] (1) Sodium, bismuth, lead, cadmium, negative electrode
A secondary battery characterized by using a composite electrode made of an alloy made of tin, a carbon material, and a binder. (2) The secondary battery according to claim 1, characterized in that an active material of sodium and cobalt oxide is used for the positive electrode.