JPS62176048A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase coulomb efficiency and to improve cycle performance to increase cycle life by using an Al-In alloy as a negative material. CONSTITUTION:An Al-In alloy is used in a negative electrode. This negative electrode is combined with a positive electrode which is rechargeable and a nonaqueous electrolyte containing an alkali metal ion to amnufacture a secon dary battery. Thereby, the negative electrode has coulomb efficiency near a theroretical value and the cycle performance is improved to sufficiency display the capabiltiy of various types of positive electrodes, and a drop in performance caused by the negative electrode is eliminated to increase the cycle life even in the repeating of high capacity charge-discharge.

Description

[Detailed description of the invention] Industrial applications The present invention has high energy density and long charge/discharge life.

Moreover, the present invention relates to a chargeable/dischargeable non-aqueous electrolyte secondary battery that has good workability, excellent stability, and reliability.

Traditionally, secondary batteries using alkali metals such as lithium as negative electrodes have been made using various interlayer compounds such as titanium disulfide (T x S z ), conductive polymer materials such as polyacetylene, etc. A secondary battery is being actively developed in which LiCQ 04 is used as a positive electrode active material and lithium perchlorate (LiCQ 04) is dissolved in an organic solvent such as propylene carbonate as an electrolyte.

These secondary batteries are characterized by the use of lithium, lithium alloy, or the like for the negative electrode, so they can have high battery voltage and high energy density.

Problems to be Solved by the Invention However, there are still very few examples of this type of secondary battery being put into practical use. The main reasons for this are a short charging/discharging cycle life and a low charging/discharging efficiency (coulombic efficiency), which is largely due to deterioration of the negative electrode. That is, when lithium is used as a negative electrode, when lithium ions in the electrolyte are deposited on the lithium negative electrode plate during charging, it is difficult to deposit homogeneously, and dendrite (dendritic) lithium is generated.
Phenomena such as penetrating the separator between the positive and negative electrodes and causing a short circuit, or lithium depositing in fine particles and falling off, may occur.
This is because the cycle life is significantly reduced.

For this reason, various methods have been proposed in the past for the purpose of improving the drawbacks of such negative electrodes, but these proposals still have various problems. For example, proposals have been made to use alloys of lithium, aluminum, silver, lead, etc. as negative electrodes, but in the case of lithium-aluminum alloys, although dendrite formation is not observed, repeated charging and discharging will cause the electrode (negative electrode) to Atomization and collapse of alloy α
Lithium-lead alloys have drawbacks such as unsatisfactory coulombic efficiency due to the low lithium diffusion rate in the phase6.Also, lithium-lead alloys have the disadvantage that the electrode collapses due to repeated charging and discharging.
In addition to being more aggressive than aluminum alloys, alloys with low lithium concentrations also have problems such as poor coulombic efficiency.
Silver alloys have a problem in that they have a low electrochemical alloy formation rate and can only be used in a micro current range.

Furthermore, it has recently been proposed to use an alloy containing tin, lead, bismuth, and cadmium as main components for the negative electrode (Japanese Patent Laid-Open No.
9-163755 to 163759゜163761), although the atomization phenomenon caused by repeated charging and discharging is improved compared to aluminum and lead alloys, the coulombic efficiency is equivalent to or slightly higher than that of lithium-aluminum alloys. However, it is still not fully satisfactory as a secondary battery negative electrode with high capacity and long life.

As described above, there are few conventional negative electrodes for nonaqueous electrolyte secondary batteries that are practically satisfactory, and it is therefore desired to develop negative electrode materials that have a large amount of alkali metal storage, high Coulombic efficiency, and long cycle life.

The present invention was developed in view of the above circumstances, and has a high energy density, a long charge/discharge cycle life, and is easy to work with.
The purpose of the present invention is to provide a highly reliable non-aqueous electrolyte secondary battery with good rollability.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte containing alkali metal ions, a rechargeable positive electrode, a nonaqueous electrolyte that absorbs alkali metal ions during charging, and a non-aqueous electrolyte that absorbs alkali metal ions during discharging. In a nonaqueous electrolyte secondary battery equipped with a negative electrode that releases alkali metal ions, an alloy of indium and aluminum is used as a material forming the negative electrode.

That is, the present inventors have conducted intensive studies on negative electrode materials that can improve coulombic efficiency and cycle life, especially through repeated charging and discharging at high charge/discharge capacity. Afl-
As shown in the experimental examples described below, the AQ-In alloy has a high coulombic efficiency even when repeated charging and discharging at a high capacity, and the decrease in capacity and coulombic efficiency due to repetition is small. It has been found that the material has excellent alkali metal ion occlusion and release capabilities, exhibits excellent negative electrode properties, and has very good properties as a negative electrode material for non-aqueous electrolyte secondary batteries. And actually this person α-
When a secondary battery is constructed by combining a negative electrode made of an In alloy with a rechargeable positive electrode and an electrolytic solution containing alkali metal ions and repeatedly charged and discharged, very good performance that can achieve the above objectives is obtained. I found out.

In addition, secondary batteries are normally used under harsh conditions, with the negative electrode voltage being as high as -3V compared to standard hydrogen electrodes, and being charged and discharged more than 1000 times. Many of the solvents used in the electrolyte cause reduction reactions and decomposition on the surface of the negative electrode, resulting in deterioration, which can have a negative impact on battery performance such as the cycle life and Coulombic efficiency of secondary batteries. However, when using the above-mentioned negative electrode material, propylene carbonate and dimethoxyethane are used as solvents constituting the non-aqueous electrolyte.

When a mixed solvent with one or more selected from tetrahydrofuran and γ-butyrolactone is used, almost no deterioration is observed in these solvents.

Furthermore, we discovered that battery performance such as cycle life and coulombic efficiency would be even better, and that we could obtain revolutionary battery performance that could withstand practical use than ever before, which led us to complete the present invention. be.

The present invention will be explained in more detail below.

As described above, the secondary battery according to the present invention comprises a negative electrode made of an aluminum-indium (AQ-In) alloy as a negative electrode material, which is combined with a rechargeable positive electrode and a non-aqueous electrolyte containing alkali metal ions. The company manufactures secondary batteries.

Here, the AQ-In alloy composition used in the present invention is not necessarily limited, but may contain 20 to 95 mol% of aluminum.
In particular, those containing 30 to 80 mol% are preferable.

When forming a negative electrode using this AQ-In alloy, Al
The negative electrode may be formed into a rolled sheet of 2-In alloy, or AQ-In alloy powder may be molded with a suitable binder, and there are no particular restrictions on the form of the negative electrode. In addition, AQ
-In alloy has excellent rollability and good sheet formability, so it has good workability when forming a sheet-like negative electrode. Further, it is preferable to use the AQ-In alloy in a porous body having continuous pores, such as a molded body of AQ-In alloy powder, since this increases the surface area of the negative electrode.

The material used for the positive electrode of the secondary battery of the present invention is not particularly limited, and can be appropriately selected and used depending on the purpose. For example, TiO□, Cr20. .

V2O9,V,O□,,MnO2,Cub,Mob.

Metal oxides such as Cu 5 Vz Ota, TiS2. F
eS.

Cu Co S 4. Metal sulfides such as M o S, NbSe3. Examples include metal selenides such as VSe2. In addition, polymers of benzene and its derivatives such as polyacetylene, polybenzene, polyparaphenylene, polyaniline, polytriphenylamine, poly(dibutoxyphenylene), polyphenylene vinylene, polypyridine, polyquinoline, polythiophene, polyfuran, polypyrrole, anthracene, naphthalene, etc. Organic conductive polymer materials such as polymers of hetero or polynuclear aromatic compounds can also be suitably used as positive electrode materials.

The electrolyte constituting the secondary battery according to the present invention is a compound consisting of a combination of an anion and a cation, and examples of the anion are PF, -, and 5bFG-.

Halide anions of group VA elements such as AsF, -, 5bCQ, -, halide anions of group HA elements such as BF4-, AQCQ, -, I-(I3-)t B
Halogen anions such as r-tCQ-, perchlorate anions such as CQ O4-, HF2-, CF, So, -.

Examples include 5CN-, So"-, H3O4-, but are not necessarily limited to these anions. Also, the cation is LL".

Alkali metal ions such as Na'', ni+, Mg''wCa
In addition to alkaline earth metal ions such as ", Ba"+, Zn
", AQ3+, and the like, and further examples include quaternary ammonium ions such as R4N+ (R represents hydrogen or a hydrocarbon residue), but the cations are not necessarily limited to these cations.

Specific examples of electrolytes having such anions and cations include LiPFG, Li5bF, and LiAsF.

LiCQ O,, LiI, LiBr, LiCQ, N
aP FG.

Na5bFs, NaAsF5. NaCQ O,, NaI
, KP FG.

K 5bFat KAsF,, KCQ O4, LiB
F.

L z A Q CQ 4 y L iHF 21
L x S CN + Z n S O4tZ n
Iz, Z n B r'2t A O2 (S 04)
z* A Q CQitAQBr,,AQl,,KS
CN, Li503CF,.

(n C4Ht)4NAsF6. (n C4H7)
4NPF@.

(n -C4Ht)4 N CQ O,, (n -C,
H,),N B F4゜(C2H,)4NCQO4,(
Examples include n-C4H, )4NI, and the like. Among these, LiCQO4°LiBF and LiPF,
etc. are suitable.

Note that the above-mentioned compound is usually used in a state dissolved in a solvent, and in this case, the solvent is not particularly limited, but a relatively highly polar solvent is preferably used. Specifically, propylene carbonate.

Ethylene carbonate, tetrahydrofuran.

2-Methyltetrahydrofuran, dioxolane.

Glymes such as dioxane, dimethoxyethane, diethylene glycol dimethyl ether, lactones such as γ-butyrolactone, phosphoric acid esters such as triethyl phosphate, boric acid esters such as triethyl borate,
Sulfur compounds such as sulfolane and dimethyl sulfoxide, nitriles such as acetonitrile, dimethylformamide,
Amides such as dimethylacetamide, dimethyl sulfate, nitromethane, nitrobenzene, dichloroethane, etc.
Mention may be made of species or mixtures of two or more species. Among these solvents, a mixed solvent of propylene carbonate and one or more selected from dimethoxyethane, tetrahydrofuran, and γ-butyrolactone is suitable for the purpose of the present invention, as described above. By using a mixed solvent, electrolytes such as L i B F 4 can be dissolved at a high concentration of about 5 mol/Q.
It also has the effect of forming a secondary battery with high energy density.

In addition, when using a mixed solvent with the above-mentioned specific propylene carbonate in the non-aqueous electrolyte according to the present invention, the proportion of propylene carbonate in the mixed solvent is 10 to 9.
Setting the content to 0% by volume, particularly 40 to 60% by volume, is even more effective for the purpose of the present invention.

The secondary battery of the present invention is usually constructed by interposing an electrolyte between the positive and negative electrodes, but in this case, a separator can be interposed between the positive and negative electrodes to prevent short circuiting of current due to contact between the two electrodes. As the separator, it is possible to use porous materials that allow the electrolyte to pass through or be contained therein, such as nonwoven fabrics, woven fabrics, and nets made of synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene.

As explained above, in the secondary battery of the present invention, by using the 80-In alloy as the negative electrode material, the negative electrode has a coulombic efficiency close to the theoretical value and has good cycle characteristics. This makes it possible to fully utilize the capabilities of various positive electrodes, eliminate as much as possible the problem of deterioration in battery function caused by negative electrodes, and ensure that cycles are maintained even after repeated charging and discharging at high charging and discharging capacities. This results in a good service life. Furthermore, in combination with this negative electrode material AQ-In alloy, propylene carbonate, dimethoxyethane,
When a mixed solvent with one or more selected from tetrahydrofuran and γ-butyrolactone is used, the solvent does not decompose and deteriorate, and a nonconductor film is not formed on the negative electrode. This makes it possible to put into practical use secondary batteries with even better battery performance such as cycle life.

Next, an experimental example will be shown. In addition, in this experimental example, in order to evaluate the negative electrode performance (electrochemical absorption and desorption ability of alkali metal) of the AQ-In alloy independently of the positive electrode, Afl-In alloy, AQ, and an In plate were used as the working electrode. Assemble a half-cell with lithium metal foil as the opposite electrode.

This study investigated the electrochemical occlusion and desorption of lithium into the working electrode.

[Experimental Example 1] A Q containing 50 mol% In with a thickness of 0.2 mm
A sample of -I n alloy foil punched to 19 mm diameter was used as the working electrode, LL metal foil punched to 18 mm diameter was used as the counter electrode, and dehydrated propylene carbonate and dehydrated dimethoxyethane were mixed in equal amounts in a volume ratio. LiBF in mixed solvent
A half cell was constructed by assembling the test cell shown in FIG. 1 in a clove box purged with argon, using a separator sufficiently impregnated with a 3 mol/Q solution of 4 as an electrolyte.

In FIG. 1, 1 is a stainless steel container, 2 is a Teflon cell container, and 3 is a working electrode.

4 is a counter electrode, and 5 is a separator.

Next, using the above half cell, it was discharged at 1 mA for 10 hours in an argon-substituted glass bottle to absorb lithium ions into the working electrode, and after measuring the open circuit voltage (Voc) between the two electrodes, Terminal voltage is 1.5 at 1mA
A charge/discharge test was conducted by repeatedly charging the battery until the battery reached (3) and releasing lithium ions to the working electrode.

As a result, the Voc in the first cycle is 0.6v, and 1
After 00 charge/discharge cycles, there was almost no decrease in capacity or coulombic efficiency, and the coulombic efficiency was 98.5% at the 10th cycle, 98% at the 50th cycle, and 97.5% at the 100th cycle. there were. In addition, although a condition was adopted in which the capacity was increased by applying 2 mA for 40 hours in the 15th cycle, the coulombic efficiency showed 98%, and no decrease was observed due to the increase in capacity.

After such a severe charge/discharge test of 100 times, the half cell was disassembled and the AQ-In alloy state of the working electrode was examined.1 Except for the loss of gloss on the surface, the particles were mostly fine. had not happened.

[Experimental Example 2] A battery similar to Experimental Example 1 was made except that an AQ foil of the same size as the working electrode of Experimental Example 1 was used for the working electrode, and a charge/discharge test was conducted under the same conditions, but at the 80th cycle. Since the coulombic efficiency had already fallen below 50%, the test was discontinued.

As a result of the above test, the Voc at the first cycle was 0.3 ■, and the coulombic efficiency was 92% at the 10th cycle and 78% at the 50th cycle.

When the half-cell after the charge/discharge test was disassembled and the state of the AQ metal at the working electrode was observed, it was found that it had become atomized and did not retain its shape.

[Experimental Example 3] Same as Experimental Example 1 except that 3 mol/Q of Li B F4 was dissolved in a mixed solvent in which dehydrated propylene carbonate and dehydrated tetrahydrofuran were mixed at equal volume ratios as the electrolyte. A similar battery was created and a charge/discharge test was conducted under the same conditions.

As a result, Voc in the first cycle is 0.6V, and 1
After 00 charge/discharge cycles, there was almost no decrease in capacity or coulombic efficiency, and the coulombic efficiency was 99.0% at the 10th cycle and 99.0%+ at the 50th cycle.
It was 98°5% at the 100th cycle.

Note that similar effects were obtained when a mixed solvent of propylene carbonate and γ-butyrolactone was used as the solvent of the electrolytic solution.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

〔Example〕

The same AQ-In alloy foil as in Experimental Example 1, in which lithium ions equivalent to 10 mAH were electrochemically occluded, was used as the negative electrode, and a 18 mm foil synthesized by electrolytic polymerization was used.
Polyaniline with a diameter of 72 mm was used as the positive electrode, and after the separator and the polyaniline positive electrode were sufficiently impregnated with the same electrolytic solution as in Experimental Example 1, a battery as shown in FIG. 1 similar to Experimental Example 1 was constructed.

It was used as a secondary battery.

This secondary battery has a terminal voltage of 2. Discharge until OV,
Next, charging was performed until the terminal voltage reached 3.2V.

This charging and discharging was repeated, and the discharge capacity and coulombic efficiency were examined for each charging and discharging cycle.

FIG. 2 shows the results of changes in discharge capacity for each charge/discharge cycle.

From the results shown in Figure 2, the discharge capacity hardly changes even when the charge/discharge cycle reaches 100 cycles, and the coulombic efficiency hardly changes at 98-99% until the 10th cycle, confirming the effect of the present invention. It was done.

[Comparative example]

A secondary battery was constructed in the same manner as in the example except that an AQ foil negative electrode was used in place of the Al--In alloy foil negative electrode of the example, and the polyaniline weight of the positive electrode was changed to 70 cm.

This secondary battery has a terminal voltage of 2. Discharge until Ov,
Next, charging was performed until the terminal voltage reached 3.5V.

This charging and discharging was repeated, and the discharge capacity for each charging and discharging cycle was examined in the same manner as in the examples.

The results of changes in discharge capacity for each charge/discharge cycle are also shown in FIG. 2.

As a result, the capacity decreased to 50% or less of the initial capacity after 55 to 60 cycles, indicating a significant change in capacity.

Here, this battery was disassembled to create a whole battery with lithium foil as the negative electrode on the positive electrode side and a half battery with lithium as the counter electrode on the aluminum foil side. Next, connect all the batteries to 1mA
When the terminal voltage is 2. When the battery was discharged to OV, 40% of the initial capacity could be discharged. On the other hand, half battery charge 1
? t (release of lithium ions) revealed that release was not possible. Therefore, it was inferred from this that the decrease in the capacity of the battery was caused not only by the deterioration of the negative electrode but also by the unbalanced charge amount between the positive and negative electrodes.

The reason for this is that the Coulombic efficiency of polyaniline is 98-99.
%, whereas that of aluminum foil is 92-93%.
This is thought to be due to the fact that as the cycle progresses, the polyaniline side is doped with anions corresponding to the difference in Coulombic efficiency between the two and accumulates. Since the coulombic efficiency was equivalent to that of polyaniline, it was confirmed that there was no decrease in capacity as in the comparative battery.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a test cell used to examine the negative electrode characteristics of the AQ-In alloy of the present invention, and FIG. 2 is a graph showing changes in capacity of batteries of Examples and Comparative Examples.

Claims (1)

[Scope of Claims] 1. A non-aqueous electrolyte containing alkali metal ions, a rechargeable positive electrode, and a negative electrode that occludes alkali metal ions during charging and releases alkali metal ions into the electrolyte during discharge. A non-aqueous electrolyte secondary battery comprising: a material forming the negative electrode made of an alloy of indium and aluminum. 2. Claim 1, wherein the solvent constituting the nonaqueous electrolyte secondary battery is a mixed solvent of propylene carbonate and one or more selected from dimethoxyethane, tetrahydrofuran, and γ-butyrolactone. secondary battery.