JPH07220758A - Lithium battery - Google Patents

Abstract

PURPOSE:To effectively suppress decreasing storage performance by making alkaline metal fluoride coexist in a lithium battery using lithium salt containing fluorine as a solute. CONSTITUTION:A battery is prepared in such a manner that a positive electrode 6 and a polypropylene-made separator 5 impregnated with an organic electrolyte are arranged in a stainless steel-made case 1 serving concurrently as a positive electrode terminal, to seal an opening part through a gasket 4 by a seal plate 2 concurrently serving as a stainless steel-made negative electrode terminal with a negative pole 3 brought into contact with an internal wall. The positive electrode 6, by adding carbon powder as a conductive agent to a lithium cobalt compound oxide, and the negative electrode 3, by adding fluororesin powder respectively as a binding agent to graphite, are prepared by pressure molding heat treatment. In the electrolyte, lithium phosphate hexafluoride is fused in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate, to add kalium fluoride used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium battery having high energy density and high reliability as a power source for driving electronic equipment or a memory holding power source.

[0002]

2. Description of the Related Art With the rapid miniaturization and weight reduction of electronic equipment, the development of a secondary battery that is smaller, lighter in weight and high in energy density, and that can be repeatedly charged and discharged with respect to the power source battery The demand is increasing. Non-aqueous electrolyte secondary batteries are the most promising secondary batteries that meet these requirements.

Various positive electrode active materials for non-aqueous electrolyte secondary batteries such as titanium disulfide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide have been investigated. ing. Among them, lithium cobalt composite oxide (Li
xCoO ₂ ) and spinel type lithium manganese oxide (Li
_{Since x} Mn ₂ O ₄ ) charges and discharges at an extremely noble potential of 4 V (Li / Li ⁺ ) or more, a battery having a high discharge voltage can be realized by using it as a positive electrode.

As a negative electrode active material for a non-aqueous electrolyte secondary battery, various materials such as metallic lithium, Li-Al alloys capable of inserting and extracting lithium, and carbon materials have been studied. Among them, carbon materials are particularly preferable. Has the advantage that a battery with high safety and long cycle life can be obtained.

As the lithium salt, lithium perchlorate, lithium trifluorotrimethanesulfonate, lithium hexafluorophosphate, etc. are generally used. Among them, lithium hexafluorophosphate has been widely used in recent years because of its high safety and high ionic conductivity of the dissolved electrolyte.

However, a lithium cobalt composite oxide (Li _x CoO ₂ ), a spinel type lithium manganese oxide (LixMn ₂ O ₄ ) or the like which operates at a noble potential is used for the positive electrode, and lithium hexafluorophosphate or the like is used as an electrolyte. A battery using a lithium salt containing fluorine has a problem that the storage performance of the battery is poor.

[0007]

The present invention provides a lithium battery comprising a negative electrode made of lithium, a lithium alloy or a substance which absorbs and releases lithium ions, a positive electrode, and a non-aqueous electrolyte containing a lithium salt containing fluorine. The present invention aims to solve the above-mentioned problems by allowing a fluoride of an alkali metal to coexist in the battery.

[0008]

When the lithium battery using the lithium salt containing fluorine as the solute is stored at high temperature for a long time, the discharge capacity is reduced. As a result of investigating the cause of this, it was found that the HF produced by the decomposition reaction of the water contained in the battery system and the lithium salt reacted with the negative electrode active material and consumed lithium as the active material, resulting in a decrease in the discharge capacity. It was Therefore, as a result of adding a fluoride of an alkali metal into the battery, it was possible to effectively suppress a decrease in charge / discharge capacity due to storage of the battery. It is considered that this is because the fluoride of the alkali metal effectively captured HF.

[0009]

EXAMPLES The present invention will be described below with reference to preferred examples.

The positive electrode was a lithium-cobalt composite oxide prepared by mixing lithium carbonate and cobalt trioxide in an atomic ratio of lithium: cobalt of 1: 1 and pyrolyzing in air at a temperature of 700 ° C. for 16 hours. (LixCoO ₂ ) and carbon powder as a conductive agent and fluororesin powder as a binder were mixed at a weight ratio of 90: 3: 7, and the mixture was pressure-molded and then vacuum dried at a temperature of 250 ° C. It was done.

The negative electrode is prepared by mixing graphite and fluororesin powder as a binder in a weight ratio of 91: 9, press-molding the mixture, and then vacuum drying at 250 ° C.

FIG. 1 is a vertical sectional view of a battery. In this figure, 1 is a case that also functions as a positive electrode terminal made by stamping a stainless steel (SUS316) steel plate, and 2 is stainless steel (SUSU316)
It is a sealing plate that also functions as a negative electrode terminal made by punching a steel plate, and the negative electrode 3 is in contact with its inner wall. 5 is a separator made of polypropylene impregnated with an organic electrolyte,
Reference numeral 6 denotes a positive electrode, and the opening end of the case 1 which also functions as a positive electrode terminal is caulked inward, and the inner periphery of the sealing plate 2 which also functions as a negative electrode terminal is tightened via a gasket 4 to hermetically seal.

Ethylene carbonate (E
C), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 2: 2: 1, and lithium hexafluorophosphate was dissolved at a concentration of 1 mol / liter. Further, potassium fluoride (KF) powder corresponding to 1 wt% of the electrolytic solution was added to the electrolytic solution, and about 150 μl of the suspension was injected.

The organic electrolyte secondary battery of the present invention using the above positive electrode plate, negative electrode plate, electrolytic solution and positive electrode can is referred to as (A).

In this embodiment, a battery of the present invention having the same structure except that sodium fluoride (NaF) is used instead of potassium fluoride is referred to as (B). further,
For comparison, a comparative battery having the same structure as the battery of the present invention except that no alkali metal fluoride is added to the battery is referred to as (A).

Next, these batteries are charged at a constant current of 2.0 mA until the terminal voltage reaches 4.2 V, and then at the same constant current of 2.0 mA until the terminal voltage reaches 3 V. Charge and discharge cycle life test to discharge 10 at room temperature
I went through a cycle. After stopping in a charged state, it was stored in a constant temperature bath at 60 ° C. for 30 days. After storage, the battery capacity was confirmed by carrying out 5 cycles of charge and discharge under the same conditions as before storage. Table 1 shows the discharge capacities of each battery before storage (10th cycle) and after storage (5th cycle).

[0017]

[Table 1] As is clear from the results of Table 1, the comparative battery (a) has a decreased battery capacity after storage of about 20%, while the batteries of the present invention (A) and (B) have a decreased battery capacity. Few.

In the above examples, the case where the alkali metal fluoride is added to the electrolytic solution is used, but the addition method is not particularly limited, and it is allowed to coexist in the separator, the electrode, or the battery such as the void of the battery. Then, the same effect can be obtained. Further, the addition amount is not particularly limited, and the same effect can be obtained by adding the lithium salt at a concentration of 0.1% or more. Since the alkali metal fluoride does not adversely affect the battery performance, for example, a method of filling the gap between the case and the electrode element of a coin-shaped, cylindrical or prismatic battery can be considered. In this case, in addition to improving the storage performance of the battery, the reliability of the battery against vibration and shock is also improved. Further, in the above embodiment, the case where K and Na are used as the alkali metal has been described, but similar effects can be obtained with other alkali metals, and one or more kinds of alkali metals may be mixed and used.

In the above examples, the case where the lithium cobalt composite oxide is used as the positive electrode active material has been described. However, titanium disulfide, manganese dioxide, spinel type lithium manganese oxide (LixMn ₂ O ₄ ), vanadium pentoxide and Various materials such as molybdenum trioxide can be used. Although a carbon material was used as the negative electrode, the negative electrode active material is basically not limited when the positive electrode of the present invention is used, and the negative electrode active material used in the conventional lithium battery, for example, pure lithium, lithium alloy, etc. Can be used. Further, in the above-mentioned embodiment, the application example to the secondary battery has been described, but the same effect can be obtained in the primary battery.

Further, the electrolytic solution which is a lithium ion conductive substance and the solid ionic conductor are not basically limited, and those used in conventional lithium batteries can be used. Examples of the organic solvent include cyclic esters such as ethylene carbonate which is an aprotic solvent and ethers such as tetrahydrofuran and dioxolane. These can be used alone or in a mixture of two or more kinds. As the solid ionic conductor, any substance having lithium ion conductivity can be used. A typical example thereof is polyethylene oxide.

Also, the supporting electrolyte dissolved in such a non-aqueous solvent or solid ionic conductor is not basically limited. For example, LiAsF ₆ , LiPF ₆ , LiBF
₄ , one or more of LiCF ₃ SO _{3 and the} like can be used.

Although the batteries according to the above-mentioned embodiments are all coin type batteries, the same effect can be obtained by applying the present invention to cylindrical, prismatic or paper type batteries.

[0023]

As described above, in a lithium battery using a lithium salt containing fluorine as a solute constituting a non-aqueous electrolyte, the coexistence of an alkali metal fluoride in the battery causes problems specific to this type of battery. It is possible to effectively suppress a decrease in storage performance, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing an internal structure of a button battery which is an example of a non-aqueous electrolyte secondary battery.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Negative Electrode 4 Gasket 5 Separator 6 Positive Electrode

Claims (1)

[Claims] 1. A lithium battery comprising a negative electrode made of lithium, a lithium alloy or a substance which absorbs and releases lithium ions, a positive electrode and a non-aqueous electrolyte containing a lithium salt containing fluorine. Lithium battery characterized by the coexistence of compounds.