JP3451601B2 - Lithium battery - Google Patents

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 a substance which absorbs and releases lithium ions, a positive electrode, and a non-aqueous electrolyte containing a lithium salt containing fluorine. In order to solve the above problems by coexisting an alkali metal fluoride other than the above, or by coexisting a lithium fluoride in the battery, except for the one obtained by adding and mixing the lithium fluoride to the negative electrode carbon material. It is a thing.

[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, except for the result of allowing a fluoride of an alkali metal other than lithium to coexist in the battery, or a mixture of the negative electrode carbon material and the fluoride of lithium added and mixed, the fluoride of lithium is added to the battery. As a result of coexistence, 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 for hermetically sealing.

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 embodiments, the case where the alkali metal fluoride is added to the electrolytic solution is used, but the addition method is not particularly limited, and the alkali metal fluoride other than lithium is allowed to coexist in the battery. In this case, it may be allowed to coexist in the battery such as in the separator or the electrode or in the void of the battery. When the lithium fluoride is allowed to coexist in the battery, the negative electrode carbon material is mixed with the lithium fluoride . Other than the above, the same effect can be obtained if they coexist in the battery such as in the separator or the electrode, or in the void of the battery.
Further, the addition amount is also not particularly limited and is 0.
Similar effects can be obtained by adding at a concentration of 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 embodiments, the case where the lithium cobalt composite oxide is used as the positive electrode active material has been described. However, titanium dioxide, manganese dioxide, spinel type lithium manganese oxide (Li _x Mn ₂ O ₄ ), vanadium pentoxide are used. Various materials such as and molybdenum trioxide can be used. In addition, as the negative electrode active material, a material that absorbs and releases lithium ions, such as a lithium alloy and a carbon material used in conventional lithium batteries, can be used.

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]

INDUSTRIAL APPLICABILITY As described above, in a lithium battery using a lithium salt containing fluorine as a solute constituting the non-aqueous electrolyte, a fluoride of an alkali metal other than lithium coexists in the battery, or a negative electrode carbon material. Li to
Coexistence of fluoride of lithium in the battery, except for addition and mixing of fluoride of thium, can effectively suppress deterioration of storage performance, which is a problem peculiar to this kind of battery, 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 Seal plate 3 Negative electrode 4 gasket 5 separator 6 Positive electrode

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 6/16

Claims (2)

(57) [Claims] 1. A lithium battery comprising a negative electrode made of a substance capable of occluding and releasing lithium ions, a positive electrode, and a non-aqueous electrolyte containing a lithium salt containing fluorine.
A lithium battery characterized in that an alkali metal fluoride other than lithium coexists. 2. A lithium battery comprising a negative electrode made of a substance capable of occluding and releasing lithium ions, a positive electrode, and a non-aqueous electrolyte containing a lithium salt containing fluorine, wherein lithium fluoride is allowed to coexist in the battery. A lithium battery characterized by. However, the negative electrode carbon material contains lithium fluoride.
Excluding those added and mixed.