JPH046759A - Secondary battery - Google Patents

Abstract

PURPOSE:To improve various characteristics by mixedly using sodium-lead alloys with multiple compositions for a negative electrode. CONSTITUTION:In a nonaqueous electrolyte secondary battery using a sodium- lead alloy, or a composite body of a sodium-lead alloy, a carbon material and a binder, or a composite body of a sodium-lead alloy, a conducting polymer material and a binder for a negative electrode, sodium-lead alloys with two different compositions: one having the sodium atomic ratio 2.5 or above against lead 1 and the other having the sodium atomic ratio less than 2.5 against lead 1, are mixedly used to form the negative electrode with the sodium atomic ratio 0-4.0 against lead 1. When this negative electrode is used, a secondary battery with improved characteristics such as high energy density, a long cycle life and a low self-discharge rate is obtained.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention provides a battery with high voltage, low self-discharge (long cycle life, and high energy density with good coulombic efficiency during charging and discharging). Regarding secondary batteries.

[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
~144i1984) provides 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 compose conductive polymers, but these have been proposed by A. N. Dey, J.
m.

Sac,, 118. No, 10. P1547~
154911971), 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.
USP 4,668,596 filed by i Inc.
, 4.753, 858, etc.

[Problem to be solved by the invention]

By the way, as mentioned above, despite research in various fields on secondary batteries that use alkali metals as negative electrodes and operate at room temperature, it has not yet been possible to completely suppress the reactivity between the alkali metals and the electrolyte. However, there is still no product that has gained a market comparable to general-purpose secondary batteries.

However, there are some extremely small capacity types (l■Ah or lomAh).
) lithium-based secondary batteries are on the market. In addition, Canada's 10LI ENERGY LIMITED is connected to the positive electrode.
A relatively high capacity (6
Although a 00mAhl secondary battery was commercialized, the reversibility of charge/discharge cycles, high-speed charge/discharge characteristics, and overdischarge characteristics did not exceed that of a nickel-cadmium secondary battery of the same shape, and the energy density was improved. However, it lacks versatility.

The main reason why this lithium-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.

The problem to be solved by the present invention is to improve the above-mentioned problems and provide a secondary battery with excellent various performances.

[Means for Solving the Problems J] In view of the above-mentioned problems, the inventors of the present invention have made extensive studies and found that the negative electrode is made of a sodium-lead alloy or a composite of a sodium-lead alloy, a carbon material, and a binder. The inventors have discovered that a non-aqueous electrolyte secondary battery with excellent performance can be obtained by using a mixture of two or more types of sodium-lead alloys, and have completed the present invention.

Instead of using lithium or lithium alloys, which are commonly used for negative electrodes, we use sodium-lead alloys, composites of sodium-lead alloys, carbon materials, and binders, or sodium-lead alloys or sodium-lead alloys, carbon materials, and binders.
The reason for using a composite of a lead alloy, a conductive polymer, and a binder is as follows. That is, the redox potential of sodium is higher than that of lithium, and its reactivity with battery solvents is accordingly milder, and the reversibility of the electrode is better. Furthermore, by using a sodium alloy, the reactivity between sodium and a solvent etc. can be greatly suppressed.

Therefore, the stability and reversibility of the negative electrode are extremely excellent, and the inventors have already filed a patent application for a secondary battery using the negative electrode in 1983.
- Application has been filed under No. 169384 etc.

However, even when this negative electrode is used, it is difficult to prevent it from reacting with the electrolyte, impurities in it, or impurities attached to the positive electrode or container.The interface between the negative electrode and the electrolyte gradually It reacts with the above impurities, etc., and the conductivity of the reaction area decreases.

In particular, this side reaction often occurs electrochemically, and tends to occur in areas where current is concentrated during normal charge/discharge reactions. If this side reaction occurs on the surface of the current collector or on the negative electrode surface that is in contact with the current collector, even if the negative electrode itself remains active as an electrode, current collection performance will deteriorate, battery performance will deteriorate, and the battery life will be shortened. become.

However, if a mixture of two or more types of sodium-lead alloys with different alloy compositions is used, there will be areas where the amount of sodium is high and areas where the amount of sodium is low, creating a localized battery that will age and exhibit superior battery performance.

This effect not only extends the charge/discharge cycle life of the battery, but also improves self-discharge characteristics, rapid charge/discharge performance, etc., and the benefits are significant.

The mixing of alloys here means physical mixing, and the atomic ratio of sodium to 1 atom of lead in the alloy obtained by melting and synthesis is between 0 and 4.0, and each atomic ratio within that It is the physical mixing of two or more types of alloys with different values.

For example, an alloy mixture in which a crushed alloy with an atomic ratio of sodium to 1 lead atom of 2.0 and a crushed alloy with a atomic ratio of sodium to 1 lead atom of 30 are mixed in a mortar or the like. It is called.

Alloys of sodium and lead show no solid solution over a wide range;
Indicates an intermetallic compound. The composition of the intermetallic compound at room temperature is 1. Typically, the above atomic ratio is 3.75; 2.
5, 10, and O-, 33, and there is also a region around 0.3 that exhibits a β phase, and in regions where the atomic ratio of sodium is less than a few percent, it is thought to exhibit a solid solution. ing.

In the above mixing example, an alloy with an atomic ratio of 2.0 has an atomic ratio of 2.0.
An alloy composed of both 5 and 1.0 intermetallic compounds with an atomic ratio of 3.0 is composed of both a 3.75 atomic ratio intermetallic compound and a 2.5 atomic ratio intermetallic compound. Therefore, when mixing an alloy with an atomic ratio of 2.0 and an alloy with an atomic ratio of 3.0,
When examined by line diffraction, the atomic ratios are 1.0, 2.5, and 3.7.
The crystal peaks of each intermetallic compound of No. 5 can be confirmed.

The alloy composition to be mixed has an atomic ratio of sodium to lead 1 of 0 to 4.0, preferably 1.0 to 3.5, more preferably 1.0 to 3.0, and two or more different alloys. It is necessary to mix the compositions so that the average sodium atomic ratio during charging and discharging is between 1.0 and 3.75.

The composition of each of the preferred mixed alloys is such that at least one type has an atomic ratio of sodium to 1 lead atom of 2.5 or more, and at least one type has a sodium atomic ratio of less than 2.5 to 1 lead atom. The one is good.

The reason for this is that the local battery effect is fully exerted after the electrolyte is diluted.

The proportion of alloys to be mixed is not particularly specified, but in order to maximize the mixing effect, it is desirable that one alloy exists between 40% and 60% by weight, and the total of the remaining mixed products is The content is preferably 60% by weight to 40% by weight.

In this case, when a negative electrode made of a mixture of two or more types of sodium-lead alloys is examined using X-ray diffraction, it is found that the atomic ratio of sodium to lead is an intermetallic compound in which the atomic ratio of sodium to lead is 1 to 3.75; The presence of intermetallic compounds or 0.3 intermetallic compounds or pure lead is simultaneously confirmed.

If a sodium-lead alloy synthesized by mixing and melting as in the conventional method, the sodium content is 3.75% per 1 lead.
and 2,5 or 2.5 and 1.0, and the presence of extensive intermetallic compounds such as 3,75 and 1 is never recognized.

Moreover, although it is possible to simply use only a sodium-lead alloy as an electrode, a carbon material, a conductive polymer, or a binder may be added to form a composite electrode. 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 (there is no particular restriction).Also, the graphite may be natural graphite or artificial graphite, or it may be a fibrous black synthesized by a vapor growth method. Graphite may also be used.However, if the amount of carbon material is too large, the electrode capacity density will be reduced.A suitable amount is 10% or less based on the weight of the negative electrode.

Further, if a conductive polymer is used, polyparaphenylene, polyacetylene, polyquinoline, or a conductor thereof is preferable, and among them, polyparaphenylene is the most preferable. A suitable amount is 15% or less 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, more effective binders for negative electrode materials include, for example, olefin copolymer rubbers such as ethylene-propylene rubber (EPR), ethylene-butene rubber (EBR), and ethylene-propylene-diene rubber (
EPDM), etc., and EPDM is particularly preferred.

If too much of this binder is used, the electrode performance will be impaired. A suitable amount is 5% or less based on the weight of the negative electrode.

Among the negative electrode active materials described above, the one that most efficiently exhibits the effects of the present invention is a system in which a carbon material and a binder are added to a sodium alloy.

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.

Examples of the non-aqueous solvent to be mixed include ether compounds such as ethoxy-methoxyethane, diglyme, triglyme, tetraglyme, pentaglyme, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-3-methyldioxolane, and dioxane, especially diglyme. , triglyme, and tetraglyme are preferred.

Specific examples of sodium salts include NaPFa, NaBF,
, NaCF35Oz, NaAsF5, Na5iFs, etc., but Na has relatively high solubility in organic solvents and is electrochemically and chemically stable.
PF5 can be recommended.

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. A positive electrode whose main component is a combination with a non-#I# compound or an inorganic chalcogenide can be suitably used. Here, as the inorganic oxide, for example, CoO□
, MnO□, w03, MoO□, Mob, , ■205, etc. Examples of inorganic chalcogenides include Ti5a, MO
Examples of inorganic halides such as sSs and NtPSe3 include RuCl3, RuBr3, and Fe0C1.

Among these, Coot, MoO have high electric capacity per weight and volume, high density, and good reversibility.
Z, MoOx, and COO2 are particularly preferred. This CoO□ takes the form of a so-called interlayer compound that exists in a form containing Na'' between the eyebrows, and the interlayer expands or contracts depending on the amount of Na''.

However, Na'' also has the function of suppressing ion repulsion between oxygen atoms, so increasing the amount of Na'' does not necessarily reduce the amount of C in the host lattice.
The axes do not necessarily elongate, but the a-axes and b-axes may elongate slightly. Therefore, the change in shape of sodium cobalt oxide having COO2 as a host due to charging and discharging is relatively small, and it is less likely to disintegrate than other inorganic substances. moreover,
Since sodium cobalt oxide has high electronic conductivity, it hardly requires conductive additives. Therefore, sufficient performance as an electrode can be achieved even if a small amount of conductive additive or no conductive additive is used.

Next, the secondary battery of the present invention will be described with reference to Examples. However, the present invention is not limited to the examples.

In particular, the embodiments are explained using a coin-type battery as an example, but the present invention can be applied to any type of battery, including cylinder type, flat plate type, etc.

[Example 1 Example 1 The negative electrode was made by finely pulverizing a mixture of alloys with an atomic ratio of sodium and lead of 2.70:1.00 and 2.20:1.00 at a weight ratio of 1:1. The weight ratio of pre-mixed acetylene black and EPDM (binder) is 3.
= 1 mixture is added, the sodium alloy mixture is 92%,
Acetylene black and EPDM were mixed to a concentration of 8% to form a negative electrode active material, and the diameter was 15 m and the thickness was 300 m.
It was produced by pressure molding into a disk shape so that it had a thickness of about 100 um. When the ratio of sodium to lead in this electrode was examined by ICP elemental analysis, the ratio of sodium to lead was 244.

This electrode was measured by X-ray diffraction method, and the X-ray diffraction pattern of the intermetallic compound, Na03Pb alloy electrode, Na2□pb alloy electrode, Na2□pb alloy electrode, and Na2. It is shown in comparison with the X-ray diffraction pattern of the tsPb alloy electrode. The intermetallic compound of sodium and lead is Na
3. ysPb, Na2. The existence of sPb, Nap, oPb, Nao, and aPb is known. However, Na0
The existence of a 3Pb intermetallic compound is not necessarily confirmed, and it is said that a β-phase solid solution exists in a narrow range around it.

The standard pattern for X-ray diffraction of Na37sPb, NaPb and pure lead is JCPDS powder Diffrac.
tion File and is already known. This time, we newly included the xi1 diffraction results of Na and sPb, Nai,
X-ray diffraction of tsPb was performed and shown in FIGS. 1 and 2. The X-ray diffraction pattern in Figure 2 is in very good agreement with the JCPDS file.

On the other hand, Nap, , 6Pb alloy and Na2□pb
The X-ray diffraction patterns of the alloys are shown in FIGS. 3 and 4, both of which are Na2. sPb intermetallic compound and Na,...,Pb
It can be seen that this is an alloy consisting only of intermetallic compounds.

On the other hand, Na2. The X11 diffraction pattern of the yPb alloy is shown in Figure 5, which is composed of intermetallic compounds such as Nas, ysPl) and Na2. It can be seen that this is an alloy consisting only of sPb intermetallic compounds. On the other hand, the Na2.
Figure 6 shows the X-ray diffraction pattern of a mixed electrode of yPb alloy and Na, zPb alloy, which is clearly Naz
, tsPb and Na2. 3 of sPb and Nap, oPb
It can be seen that it is a mixture of various intermetallic compounds.

In addition, the positive electrode is made by heating and reacting Na, 0□ and CO3O4 in an oxygen atmosphere to form Nao, ? After synthesizing C0Q2 and pulverizing it, a mixture of acetylene black and tetrafluoroethylene (binder) with a weight ratio of 3:1 was added, and Nao, tcOOz was 96%, and the mixture was 4:1. % to form a positive electrode active material, and a diameter of 15%.
It was produced by pressure molding into a disc shape so that it had a thickness of about 400 μm.

The electrolytic solution used was one in which NaPF was dissolved in 1,2-dimethoxyethane at a concentration of 1 mole/I2.A polypropylene microporous film and a polypropylene nonwoven fabric were used as separators between the positive and negative electrodes. Using this method, a well-known coin-shaped cell as shown in FIG. 7 was assembled.

The voltage of this battery immediately after assembly was 2.50V. When this battery is discharged with a current of 3.0 mA, the battery voltage is 1.8
Discharge until the battery voltage reaches V, then at the same current value the battery voltage increases to 3.
．． Charge until it reaches 2V, then repeat discharging and charging.
When we investigated the discharge capacity and reversibility of this battery, the maximum discharge capacity was 17.5 mAh, and the charge/discharge efficiency was 100 mAh.
%Met. Even in the 50th cycle, it is operating smoothly with a charging/discharging efficiency of 100% and a discharge capacity of 17.3a+Ah.

Example 2 The same battery as above was assembled, charged, and charged for 60
℃, and examined the self-discharge rate after being left for 10 days.1
．． It was 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 3 The same positive electrode and electrolyte as in Example 1 were used, and the negative electrode had an atomic ratio of sodium to lead of 3.75:1.00.
96:1.00 mixed in weight ratio I:I 91%
A composite of acetylene black and EPDM mixed at a concentration of 9% was used.

This electrode's X! When one diffraction was performed, the result was as shown in FIG. Again, sa,,ysPb and Na2. sPb
It can be seen that it is a mixture of intermetallic compounds, Nap, and oPb.

This battery was first discharged from the discharging direction at a constant current value of 5 mA until the battery voltage reached 1.5 V, then charged at the same current value until the battery voltage reached 3.3 ■, after which discharging and charging were repeated. Maximum discharge capacity is 16.8n+Ah,
It took 253 cycles for the discharge capacity to drop to 85% of the maximum value, and the differential remained steady after that.

Example 4 The atomic ratio of sodium and lead in the negative electrode was 2.70:1. The same positive electrode and electrolyte as in Example 1 were used, except that a mixture of OO alloy and lead at a weight ratio of 9:1 and a mixture of acetylene black and EPDM at a weight ratio of 8% were used. When an experiment was conducted in the same manner as in Example 1, the maximum discharge capacity was 17.6*Ah, and the cycle life was 668 times. Furthermore, the self-discharge rate of this battery was examined in the same manner as in Example 2, and was found to be 1.6%.

Comparative Example 1 Example 1 except that an alloy with an atomic ratio of sodium and lead of 2.70 to 1.00 was used as the negative electrode alloy used in Example 1.
Battery performance was evaluated using exactly the same method. The results of examining this negative electrode using the X-ray diffraction method are already shown in Figure 5.
575Pb and Na2. Only intermetallic compounds of sPb were confirmed, and Na+, Opb, etc. were not found.

As a result, the maximum discharge capacity was 17.1*Ah, which was slightly lower than in Example 1, and the capacity at the 50th cycle was 16.7*Ah. This was slightly inferior to the mixed composition.

Comparative Example 2 A battery exactly the same as Comparative Example 1 was assembled, and the self-discharge rate was examined in the same manner as in Example 2, and it was found to be 2.7%.

Comparative Example 3 Using the same battery as Comparative Example 1, battery performance was evaluated in the same manner as in Example 3. As a result, the maximum discharge capacity was 15.
The cycle life until the capacity decreased to 85% at 6*Ah was 230 cycles.

Example 5 The atomic ratio of sodium and lead in the negative electrode was 3. lOO 120 mouths and 1.80 to 1. A battery experiment was carried out in the same manner as in Examples 1 and 2, except that a mixture of OO alloy at a weight ratio of 1:1 was used, and the maximum discharge capacity was 15.9*Ah.
The capacity at the 1st cycle was 15.8 Ah.

The self-discharge rate was 2.1%.

Example 6 The atomic ratio of sodium lead in the negative electrode is 2.70 to 1.00 and 3
．． A battery experiment was conducted in the same manner as in Examples 1 and 2 except that a mixture of 70:1.00 and 1.00 was used at a weight ratio of 1:2.The maximum discharge capacity was 16.411Ah, and the discharge capacity at the 50th cycle was 16.2*Ah, self-discharge rate is 2.
It was 7%.

Example 7 The atomic ratio of sodium lead in the negative electrode is 2.70 to 1.00.
．． 30:1.00 mixed at a weight ratio of 1:1 is 99
．． A battery experiment was conducted in the same manner as in Examples 1 and 2 except that a mixture of 5% EPDM and 0.5% EPDM was used, and the maximum discharge capacity was 16.9 ■Ah, and the discharge capacity at the 50th cycle was 16 At .5*Ah, the self-discharge rate was 2.1%.

Example 8 The atomic ratio of sodium lead in the negative electrode is 2.80:1.00 and 2
．． 20:1.00 mixed at a weight ratio of 1:1 is 94
% and KOVACIC method (J, Am,
ChemSoc, , 85.454-458 (19
631) and EPDM synthesized by
When a battery experiment was conducted in the same manner as in Examples 1 and 2 using a mixture of 6% with a weight ratio of 3=1, the maximum discharge capacity was 16.5*Ah, and the discharge capacity at the 50th cycle was I6. At .3*Ah, the self-discharge rate was 2.6%.

[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.
Because it has many excellent performances.

It will greatly contribute to fields that use this as a power source.

[Brief explanation of the drawing]

Figure 1 shows the X-ray diffraction pattern of Naa, sPb alloy electrode Figure 2 shows Nax, ysPb tt Figure 3 shows N
a1.98Pb //Figure 4 shows Na2. zP
b //Figure 5 shows Na2. yPb
//Figure 6 is the x#it diffraction pattern of a mixed electrode of Na2□pb alloy and Naz□pb alloy. Figure 7 is a vertical cross-sectional view of a coin-type secondary battery. The X-ray diffraction pattern of the mixed electrode of vsPb alloy is shown, and in Figs. 1 to 6 and Fig. 8, m is Na
．． tsPb shows the diffraction line peaks characteristic of all Pb compounds, * indicates the diffraction line peaks of Naz and sPb, and ■ indicates Na+. The diffraction line peak of pb is shown. In addition, the numbers in Fig. 7 are as follows: 1--Positive electrode, 2--Current collector, 3--...
-Polypropylene nonwoven fabric, 4...Polypropylene microporous film, 5...--Insulating packing, 6...-Negative electrode, 7...-Positive electrode can, 8-- ...- It is a negative electrode can.

Claims (6)

[Claims] (1) For the negative electrode, a sodium/lead alloy or a composite of a sodium/lead alloy, a carbon material, and a binder, or a sodium/lead alloy
A non-aqueous electrolyte secondary battery using a composite of a lead alloy, a conductive polymer, and a binder, characterized in that a mixture of two or more types of sodium-lead alloys with alloy compositions is used for the negative electrode. Secondary battery. (2) At least one of the alloys to be mixed has an atomic ratio of sodium to 1 lead of 2.5 or more, and at least one is a mixture of alloys in which the atomic ratio of sodium to 1 lead is less than 2.5. The secondary battery according to claim (1), which uses a negative electrode. (3) The secondary battery according to claim (1), wherein the sodium-lead alloy used for the negative electrode has an atomic ratio of sodium to 1 lead in the range of 0 to 4.0. (4) The secondary battery according to any one of claims (1) to (3), wherein the average atomic ratio of sodium to 1 lead of the sodium-lead alloy of the negative electrode during charging and discharging is within the range of 1.0 to 3.75. . (5) X-ray diffraction spectrum of the negative electrode after molding shows that the atomic ratio of sodium to lead is an intermetallic compound of 3.75:1 and an intermetallic compound of 1:1 or an intermetallic compound of 0.3:1 or pure lead. The secondary battery according to any one of claims (1) to (4), comprising a sodium-lead alloy in which is observed at the same time. (6) The secondary battery according to any one of claims (1) to (5), wherein the positive electrode is a sodium cobalt oxide.