JP3353455B2 - Organic electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte secondary battery having a high energy density and a high safety against overcharging as a power supply for driving electronic equipment or a memory holding power supply.

[0002]

2. Description of the Related Art With the rapid reduction in size and weight of electronic equipment, the development of secondary batteries that are small, lightweight, have a high energy density, and can be repeatedly charged and discharged with respect to the battery that is the power source of the electronic equipment has been developed. Demands are growing. As a secondary battery satisfying these requirements, an organic electrolyte secondary battery is most promising.

The positive electrode active material of an organic electrolyte secondary battery includes titanium disulfide, lithium cobalt composite oxide, lithium nickel composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide. Various things are being considered. In particular, lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide, and spinel-type lithium manganese oxide (LiMn ₂ O ₄ ) are charged at a noble potential of 4 V (vs. Li / Li ⁺ ) or more. Since discharge is performed, a battery having a high discharge voltage can be realized by using the positive electrode.

As the negative electrode active material of the organic electrolyte secondary battery, various materials such as lithium metal and a lithium-alkaline alloy or a carbon material capable of occluding and releasing lithium have been studied. The representative carbon material has an advantage that a battery having high safety and a long cycle life can be obtained.

[0005] The electrolyte solution is a mixture of a cyclic ester solvent such as ethylene carbonate, propylene carbonate and γ-butyrolactone and a chain ester solvent such as dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate. Lithium trifluoromethanesulfonate, lithium tetrafluoroborate,
A solution in which a lithium salt such as lithium hexafluorophosphate is dissolved is generally used. Among them, an electrolyte solution obtained by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and a chain ester solvent has high safety and high ionic conductivity and has excellent stability to a graphite negative electrode. In recent years, it has been actively used.

In a battery using a lithium-cobalt composite oxide, a lithium-nickel composite oxide, or the like for the positive electrode and a carbon material for the negative electrode, charging is performed at a battery voltage so that the charging capacity of the positive electrode does not exceed the lithium storage capacity of the negative electrode. Because of the restrictions,
No electrodeposition of metallic lithium, which causes ignition, occurs on the negative electrode. However, there is a case where the battery is overcharged by greatly exceeding a set voltage which is usually 4.1 to 4.2 V due to a failure of the charger or an erroneous use of the battery. At that time, since the charge capacity of the positive electrode exceeds the capacity of the negative electrode that can be stored, metal lithium is deposited on the negative electrode, and the risk of ignition of the battery increases.
Even if the battery does not ignite, the decomposition of the electrolyte proceeds near the battery voltage of 5 V, the internal pressure of the battery rises significantly, and the risk of the battery exploding increases. When the battery has a safety valve, it is possible to prevent the battery from being ruptured, but it is not possible to avoid loss of equipment due to leakage of electrolyte.

As a countermeasure, as described in JP-A-3-49155, a catalyst for decomposing an electrolytic solution is added to the active material to decompose the electrolytic solution at the time of overcharging such that the battery voltage exceeds 4.5V. In some cases, a safety valve provided by the generated gas shuts off a charging current. However, in addition to the complicated and expensive manufacturing mechanism of the safety valve,
Since the decomposition reaction of the electrolytic solution by the added catalyst proceeds even at a normal charging voltage, it was found that there was a problem in long-term reliability of the battery.

[0008] Therefore, an organic electrolyte secondary battery having excellent long-term reliability and having simple overcharge protection has been desired.

[0009]

Means for Solving the Problems The present invention provides a negative electrode,
In a battery provided with a positive electrode operating at a potential of V (vs. Li ^/ Li ⁺ ) or higher and an organic electrolyte, the above problem is solved by adding austenitic stainless steel powder to the positive electrode. is there.

[0010]

The dissolution potential of various stainless steels in the electrolyte was measured. LiPF ₆ , LiAsF ₆ , LiB
When using, for example, F _4, SUS430 irrespective of the type of solute and solvent, SUS434, ferritic stainless steel such as SUS447J1 is about 4~4.1V (v
s.Li/Li ⁺ ) starts dissolution, SUS304, SUS3
Austenitic stainless steels such as 10S, SUS316, and SUS317 are about 4.4 to 4.6 (vs. Li / L).
Dissolution started with i ⁺ ).

In a battery in which an austenitic stainless steel powder is added to a positive electrode operating at a potential of 4 V (vs. Li ^/ Li ⁺ ) or higher, a normal charging voltage of 4.1 to 4.2 is used.
If the battery voltage is overcharged by exceeding V, the battery voltage becomes 4.4 to 4.
When the voltage reaches 6 V, the charging current is consumed for the dissolution reaction of the stainless steel. As overcharging proceeds, electrodeposition of the dissolved metal ions on the negative electrode proceeds, and the negative electrode and the positive electrode are electrically connected via the separator. Since the charging current flows through this electric path, the charging reaction of the battery does not proceed. That is, according to the present invention, battery rupture due to overcharging,
Dangers such as ignition and liquid leakage can be avoided. However, a battery in which a ferrite-based stainless steel powder is added to a positive electrode that operates at a potential of A4V (vs. Li / Li ⁺ ) or higher has a charge current of stainless steel at a normal charge voltage of 4.1 to 4.2 V. Consumed in the dissolution reaction. Then, electrodeposition of the dissolved metal ions on the negative electrode proceeds, the negative electrode and the positive electrode are electrically connected via the separator, and the function as a battery is lost.

[0012]

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

[0013] The positive electrode was experimentally produced by the following method. Lithium-cobalt composite oxide (LiCoO ₂ ), carbon powder as conductive agent and polyvinylidene fluoride as binder
They were mixed at a weight ratio of 0: 2: 8. Further, SUS316 powder (particle size: 15%) corresponding to 1% by weight based on LiCoO ₂
μm) was added. After forming a paste with N-methyl-2-pyrrolidone, which is a solvent, the paste was applied to a titanium foil, roll-pressed, and then punched into a disc having a diameter of 15 mm. Before assembling into a battery, a vacuum drying process was performed at a temperature of 250 ° C.

[0014] The negative electrode was experimentally produced by the following method. Graphite and polyvinylidene fluoride as a binder were mixed at a weight ratio of 84:16. After forming a paste with N-methyl-2-pyrrolidone, it was applied to a copper foil, roll-pressed, and punched out into a φ16 mm disc. Before assembling into batteries, temperature 250 ℃
Was subjected to vacuum drying.

FIG. 1 is a longitudinal sectional view of a battery. In this figure, reference numeral 1 denotes a case also serving as a positive electrode terminal formed by punching a titanium plate, and 2 denotes a sealing plate serving also as a negative electrode terminal formed by punching a stainless steel (SUS316) steel plate. . Reference numeral 5 denotes a separator made of polypropylene impregnated with an organic electrolyte, 6 denotes a positive electrode, and crimps an opening end of the case 1 also serving as a positive electrode terminal, and tightens an outer periphery of a sealing plate 2 also serving as a negative electrode terminal via a gasket 4. It is hermetically sealed. As the organic electrolyte, a solution prepared by dissolving lithium hexafluorophosphate at a concentration of 1 mol / liter in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1 was used.

The organic electrolyte secondary battery of the present invention is referred to as (A). In this example, the batteries of the present invention having the same configuration except that the amounts of SUS316 stainless steel powder added were 0.3 and 0.1% by weight, respectively, are referred to as (B) and (C), respectively. . In this embodiment, S
The batteries of the present invention having the same configuration except that the particle size of the US316 stainless steel powder was 10 and 5 μm, respectively, are referred to as (D) and (E), respectively. Further, the battery of the present invention having the same configuration except that SUS317 stainless steel powder was used in place of SUS316 stainless steel powder in this embodiment is referred to as (F). The battery of the present invention having the same configuration except that SUS304 stainless steel powder was used and LiClO ₄ was used instead of LiPF ₆ was referred to as (G).

For comparison, a comparative battery having the same structure as the battery of the present invention except that no stainless steel powder was added was referred to as (a). In this embodiment, SUS430 stainless steel powder was used instead of SUS316 stainless steel powder. A comparative battery having the same configuration except that steel powder was added is called (a). Next, these batteries were charged at a constant current of 2.0 mA until the terminal voltage reached 4.2 V. , Followed by 2.0
10 charge / discharge cycle life tests were performed at room temperature at a constant current of mA until the terminal voltage reached 3 V.

Table 1 shows the discharge capacity of the battery at the tenth cycle. The result was the average value of the battery 3N.

[0019]

[Table 1] As is clear from the results in Table 1, there is no significant difference between the comparative battery (A) and the present inventions (A) to (G), but the comparative battery (A) has a remarkably small capacity. As a result of disassembly, it was found that the internal short circuit caused by the dissolution of the added stainless steel occurred in the comparative battery (a).

Subsequently, the comparative battery (A) and the present inventions (A) to (G) were continuously overcharged at a constant current of 2.0 mA. In the comparative battery (A), the battery ruptured when the electric capacity of about three times the discharge capacity was applied, but the batteries (A) to (G) of the present invention did not rupture.
The charging was stopped at the time when the electric capacity of about 20 times the discharge capacity was applied, and the result of measuring the open circuit voltage of the battery was summarized in Table 2.

[0021]

[Table 2] The batteries (A), (D), (E), (F), and (G) exhibited a voltage of 0 V due to the short circuit, and the batteries (B) and (C) exhibited a decrease in voltage due to the soft short circuit.

In the above embodiment, LiCo was used as the positive electrode active material.
Although the case where O ₂ is used has been described, 4 V (vs. Li / L
i ⁺ ) or higher, and a lithium nickel composite oxide or spinel lithium manganese oxide (LiMn ₂ O)
₄ ) etc.

Although graphite was used as the negative electrode, in using the electrolyte of the present invention, the negative electrode active material is not basically limited, and the negative electrode active material used in conventional lithium batteries, for example, metallic lithium, A lithium alloy or the like can be used.

Further, the electrolyte is not fundamentally limited, and those used in conventional organic electrolyte secondary batteries can be used. For example, examples of the organic solvent include cyclic esters such as ethylene carbonate, which are aprotic solvents, and ethers such as tetrahydrofuran and dioxolan, and a single or a mixture of two or more thereof can be used.

The solute is not fundamentally limited. For example, one or more of lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate and the like can be used.

Although the batteries according to the above embodiments are all coin-shaped batteries, the same effects can be obtained by applying the present invention to cylindrical, square or paper batteries.

As described above, the negative electrode and 4 V (vs. L
i / Li ⁺ ) In a battery including a positive electrode operating at a potential equal to or higher than an electric potential and an organic electrolyte, the safety of the battery in an overcharged state can be ensured by adding austenitic stainless steel powder to the positive electrode. Therefore, an organic electrolyte secondary battery having high energy density, excellent cycle characteristics, and high safety can be supplied at low cost, and its industrial value is great.

[Brief description of the 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]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Negative electrode 4 Gasket 5 Separator 6 Positive electrode

Claims (1)

(57) [Claims] 1. An anode comprising a negative electrode, a positive electrode operating at a potential of 4 V (vs. Li / Li +) or more, and an organic electrolyte, wherein the positive electrode is a powder to which austenitic stainless steel powder is added. Organic electrolyte secondary battery.