JPS62211861A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase the coulomb efficiency and the cycle life in high capacity charge-discharge by forming a negative electrode in a nonaqueous secondary battery with a specified alloy in which magnesium is contained. CONSTITUTION:A nonaqueous secondary battery is formed with a nonaqueous electrolyte containing an alkali metal ion, a positive electrode capable of charge- discharge, and a negative electrode which absorbs an alkali metal ion during charge and desorbs the alkali metal ion absorbed into an electrolyte during discharge. The negative electrode is formed with an alloy of one or more metals selected from a group of zinc, tin, antimony, lead, bismuth, and thallium, and magnesium, or an alloy obtained by adding an alkali metal to the above alloy. Thereby, the coulomb efficiency of the secondary battery is remarkably increased, and decrease in capacity and coulomb efficiency caused by repeated charge-discharge is retarded to increase the cycle life.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-aqueous electrolyte secondary battery that is chargeable and dischargeable, has excellent charge-discharge efficiency and cycle life, and has a high battery voltage.

Choren Jsu 1st right In recent years, memory backup for ICs, etc., and clocks.

BACKGROUND OF THE INVENTION In a wide variety of industrial fields such as automobiles, portable equipment, and audio equipment, there is a demand for secondary batteries that can be charged and discharged, have excellent charging/discharging efficiency, and cycle life, and have a high battery voltage.

Conventionally, in order to obtain such secondary batteries, alkali metals such as lithium have been used for negative electrodes, and titanium disulfide (T
Various interlayer compounds such as iS2) and conductive polymer materials such as polyacetylene are used as positive electrode active materials, and lithium perchlorate (LiCQ) is used as an electrolyte.
04) and the like dissolved in an organic solvent such as propylene carbonate are actively being developed.

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 reason is that the number of charge/discharge cycles (cycles) and life are short.

This is due to low charge/discharge efficiency (Coulombic efficiency), and a major cause of this is the large deterioration of the negative electrode. For example, when lithium is used as a negative electrode, when lithium ions in the electrolyte precipitate on the lithium negative electrode plate during charging, it is difficult to deposit homogeneously, and dendrite lithium is generated, causing a separator between the positive and negative electrodes. lithium may penetrate and cause a short circuit, or lithium may precipitate on fine particles.
It has the disadvantage that phenomena such as falling off occur, significantly reducing the cycle life.

For this reason, various methods have been proposed in the past for the purpose of improving such drawbacks of 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 disintegration of particles occur.

It has drawbacks such as unsatisfactory Coulombic efficiency due to slow lithium diffusion rate in the alloy α phase. In addition, lithium-lead alloys have problems such as electrode collapse more violently than lithium-aluminum alloys due to repeated charging and discharging, alloys with low lithium concentrations have poor coulombic efficiency, and lithium-silver alloys have problems such as electrochemical The problem is that the alloy formation rate is low, and it can only be used in the microcurrent region.

As described above, there are few conventional negative electrodes for secondary batteries that are practically satisfactory, and it is therefore desired to develop a negative electrode material that has a large capacity to absorb and release alkali metal ions, has a high Coulombic efficiency, and has a long cycle life.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery with high charge/discharge efficiency and a long cycle life.

In order to achieve the above object, the present invention includes an electrolyte containing alkali metal ions, a rechargeable and dischargeable positive electrode, an alkali metal ion which is occluded during charging, and an alkali metal ion contained in the electrolyte during discharging. In a secondary battery equipped with a negative electrode that emits
An alloy of at least one metal and magnesium, or an alloy in which an alkali metal is added to the alloy is used.

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. When used as negative electrode materials, all of these materials have higher coulombic efficiency even when repeatedly charged and discharged at a higher capacity than negative electrode materials that do not contain magnesium, as shown in the examples below. It has been found that the capacity and coulombic efficiency decrease little due to repetition, and therefore the alkali metal ion storage and desorption ability is excellent, and the negative electrode characteristics are excellent, and very good performance that can achieve the above objectives can be obtained. 1. The present invention. This is what we have come to do.

The following five inventions will be explained in more detail.

As mentioned above, the secondary battery according to the present invention has a specific magnesium-containing alloy, that is, an alloy component consisting of one or more metals selected from zinc, tin, antimony, lead, bismuth, and thallium. An alloy with magnesium, or an alloy consisting of the alloy constituents, an alkali metal, and magnesium is used as a negative electrode material, and this is combined with a rechargeable and dischargeable positive electrode and an electrolyte containing alkali metal ions to constitute a secondary battery. It is something.

Here, in the alloy of magnesium and an alloy component (hereinafter referred to as component A) consisting of one or more metals selected from zinc, tin, antimony, lead, bismuth, and thallium used in the present invention, Although its composition is not necessarily limited, it is preferable that it contains 1 to 50%, especially 5 to 20%, of magnesium in terms of atomic ratio.On the other hand, in the case of an alloy consisting of component A, an alkali metal, and magnesium, the composition is not necessarily limited. However, when an alkali metal is added to the alloy consisting of the above A component and magnesium, 1-.8
0%, especially 5 to 60% is preferable. In this case, lithium is preferably used as the alkali metal.

Note that the alloy components of the magnesium-containing alloy used in the present invention do not necessarily need to be present in a homogeneous state. That is, the magnesium-containing alloy according to the present invention can be manufactured according to various manufacturing methods. For example, all alloy components are heated and melted in a vacuum or an inert gas atmosphere, mixed uniformly, and then cooled and solidified to form an alloy. In addition to those manufactured by the method of oxidation, those manufactured by the method of electrochemically introducing an alkali metal into the alloy of component A and magnesium as required, and those manufactured by laminating an alkali metal on the alloy of component A and magnesium. , which is then immersed in an electrolytic solution of an alkali metal salt, etc. can be used.

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, Tie.

Cr, O,, V, ○s t Vs Ols v Li
Co Ox +L i Cr○2. M n O2,
Cu O, M o O,.

Metal oxides such as Cu, V, O, TiS, FeS.

CuCo54. Metal sulfides such as Mob.

Examples include metal selenides such as NbSe and VSe2. In addition, polyacetylene, polybenzene, polyparaphenylene, polyaniline, polytriphenylamine,
High organic conductivity such as polymers of benzene and its derivatives such as poly(dibu-1-xyphenylene) and polyphenylene vinylene, polymers of hetero or polynuclear aromatic compounds such as polypyridine, polyquinoline, polythiophene, polyfuran, polypyrrole, anthracene and naphthalene. Molecular materials can also be suitably used as positive electrode materials.

The compound used in the non-aqueous electrolyte constituting the secondary battery of the present invention and generating ions that can be occluded in the positive and negative electrodes is a compound consisting of a combination of an anion and a cation, and an example of the anion is PFG- ,5bF6-,A
halide anions of group VA elements such as sFG-, 5bCQG-(1), B F4-;

Halide anions of group IIrA elements such as AnCQ4-, halogen anions such as I-(I3-)+Br-, CQ-, perchlorate anions such as CQ04-, H
F2-, CF, So, -, 5CN-, 5ob-.

Examples include H5O,-, but the anion is not necessarily limited to these anions. In addition, examples of cations include alkali metal ions such as Li'', Na÷, and Ni÷.

Specific examples of electrolytes having such anions and cations include LiPF, LiSbF6゜LIAs
F @ g L z CQ O4t L iI g L
iB r +LiCQ, NaPF5. Na5bF,.

NaAs F, , NaCQO4, Na I, KPF, °
.

KSbF, KAsF, KCQO, LiBF4゜L
iAQCI2. , LiHF, , Li5CN, and the like. Among these, especially LiCQO.

1 selected from L iB F 4 and L i P F
A species or two or more species are preferred.

Note that these electrolytes are normally used in a state dissolved in a solvent, but in the present invention, a non-aqueous solvent is used as the solvent. In this case, relatively highly polar solvents are preferably used, specifically propylene carbonate, ethylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, and 2-methyltetrahydrofuran.

One or more of γ-butyrolactone, triethyl phosphate, triethyl phosphite, dimethyl sulfate, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, dimethoxyethane, polyethylene glycol, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, etc. Mention may be made of mixtures of. Among them, propylene carbonate,
One or more mixed solvents selected from γ-butyrolactone, dimethoxyethane, and tetrahydrofuran are suitable.

In addition, the electrolyte concentration in the electrolyte is in the range higher than 1moQ/Q, lower than 6mon/12, especially 2moQ/Q.
It is preferable to set the range of Q/Q to 3 taoQ/Q from the viewpoint of forming a battery with good battery performance such as discharge capacity, energy density, and charge/discharge cycle life when forming a secondary battery.

As explained above, the secondary battery of the present invention comprises magnesium and one or more metals selected from zinc, tin, antimony, lead, bismuth, and thallium as negative electrode materials. By using an alloy or an alloy in which an alkali metal is added to the alloy, the coulombic efficiency of the secondary battery can be dramatically increased.

The cycle characteristics are also good, which makes it possible to fully utilize the capabilities of various positive electrodes, and to eliminate as much as possible the problem of deterioration in secondary battery function caused by negative electrodes.
This makes it possible to put into practical use secondary batteries with high battery voltage and excellent charge/discharge efficiency and cycle life.

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

[Examples 1 to 10. Comparative Examples 1 to 6] 1cm×1c formed from the types of negative electrode materials shown in the table
mX Lam plate-shaped negative electrode A, 4cmX 4cn+X
0. Positive electrode B, 3 mo12/lit, made by depositing 1 g of polyaniline on a 4 mm PT plate by electrolytic polymerization.
Using propylene carbonate (electrolytic solution) C1 in which L i B F4 was dissolved, and a lithium plate as a reference electrode, the test cell shown in the drawing was constructed. In forming the negative electrode, a rollable negative electrode material was formed by a rolling method, and a non-rollable negative electrode material was cut out using a cutter.

The above test cell was charged at 4 mA for 25 hours to occlude lithium in the negative electrode, and then discharged at 4 mA until the negative electrode potential became 1.5 V compared to the reference electrode, and the lithium occluded in the negative electrode was removed from the electrolyte. By repeating charging and discharging,
Calculate the charging/discharging efficiency (ratio of the amount of discharged electricity to the amount of charged electricity of 100mAH) for the 1st cycle and the 10th cycle.1
The charging/discharging efficiency and cycle life as a secondary battery were evaluated from the charging/discharging efficiency of both. Note that when a lithium-containing alloy is used as the negative electrode material, since lithium is occluded in advance, charging is not performed in the first cycle, and the battery is only discharged at 4 mA for 25 hours. Further, during the repetition of the above-mentioned charging and discharging, doping and dedoping of BF4- ions are performed at the positive electrode.

The above results are also listed in Table 1.

From the results shown in Table 1, it was confirmed that the negative electrode material according to the present invention exhibited excellent charge/discharge efficiency and cycle life, which are necessary for secondary batteries.

[Brief explanation of drawings]

The drawing is a schematic diagram of an electrolytic cell used to examine battery performance.

Claims (1)

[Claims] 1. In a secondary battery equipped with a nonaqueous electrolyte containing alkali metal ions, a rechargeable and dischargeable positive electrode, and a negative electrode that stores alkali metal ions during charging and releases alkali metal ions into the nonaqueous electrolyte during discharge. , an alloy of magnesium and one or more metals selected from zinc, tin, antimony, lead, bismuth, and thallium, or an alloy in which an alkali metal is added to the alloy is used as the material forming the negative electrode. A non-aqueous electrolyte secondary battery characterized by: