JPH09231976A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent any electrical deposition of metallic lithium onto the surface of a negative electrode under an application of overcharging and further prevent a decomposing reaction of electrolyte by a method wherein a negative electrode in a nonaqueous electrolyte secondary battery contains a specified amount of aromatic hydrocarbon. SOLUTION: A negative electrode 6 is constituted such that it contains more than one kind of aromatic hydrocarbon of 1wt.% or more selected from naphthalene, anthracene and phenanthrene. With such an arrangement as above, aromatic hydrocarbon in the negative electrode 6 is reacted in reversible manner with lithium metal during overcharging operation so as to act as a kind of chemical shuttle, resulting in that a growth of electrical deposited lithium for the negative electrode 6 can be restricted and at the same time it becomes possible to prevent a decomposing reaction of electrolyte by supplying lithium to the positive electrode 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery capable of preventing the harmful effects of overcharge.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery having a negative electrode made of a carbonaceous material has attracted attention because it exhibits excellent durability with less capacity deterioration during charge and discharge cycles. This utilizes the fact that the carbonaceous material can reversibly occlude and release lithium at a base potential and reversibly form an intercalation compound between lithium and the carbonaceous material.

That is, when a non-aqueous electrolyte secondary battery is composed of a positive electrode containing a sufficient amount of lithium, a negative electrode made of a carbonaceous material and a non-aqueous lithium ion conductive electrolyte through a separator, this battery is Since the assembly is completed in the discharged state, the battery cannot be discharged unless it is charged after the assembly. When this battery is charged in the first cycle, lithium in the positive electrode is electrochemically doped between the layers of the negative electrode carbonaceous material, and then discharged,
The lithium that was doped until then is dedoped and returns to the positive electrode again. Therefore, the negative electrode potential of this type of battery usually shifts to a noble direction by discharging lithium ions when discharged, and shifts to a lesser direction by storing lithium ions when charged.

[0004]

However, in this type of battery, the following problems occur during overcharging.

That is, when a battery is charged, a large current may temporarily flow to the battery due to a failure of the charger, or the energized state may continue even if the battery reaches the end-of-charge voltage. When the negative electrode potential of the battery in such an overcharged state becomes baser than the lithium metal potential, lithium metal is deposited on the negative electrode (lithium occlusion body).

At this time, if all of the lithium intercalated in the positive electrode is released, solvent decomposition occurs in the positive electrode, and this reaction involves gas evolution, which deteriorates the electrolytic solution and raises the internal pressure of the battery. May lead to rupture and is extremely dangerous.

Further, in the negative electrode, the electrolyte in the electrolytic solution is reduced and lithium metal is deposited as described above. However, since this deposition form is dendrite-like, the electrodeposited lithium penetrates the separator and the inside There is a risk that not only will the battery become inoperable as a result of a short circuit, but the battery will explode or ignite.

In view of the above circumstances, the present invention prevents the electrodeposition of metallic lithium on the surface of the negative electrode during overcharge and also prevents the decomposition reaction of the electrolytic solution, thereby preventing the battery from bursting or igniting. It is an object to provide a non-aqueous electrolyte secondary battery that can be prevented.

[0009]

In the present invention, attention is paid to the fact that when an alkali metal is intercalated in an organic solvent, coexistence of an aromatic hydrocarbon such as naphthalene, phenanthrene, anthracene or the like causes various properties to be exhibited. did.

That is, the present invention provides a non-aqueous electrolyte comprising a positive electrode (5) containing lithium, a negative electrode (6) made of a carbonaceous material capable of reversibly doping / dedoping lithium, and a non-aqueous electrolyte. In the electrolytic solution secondary battery (1), the negative electrode is
It is configured to contain 1% by weight or more of one or more kinds of aromatic hydrocarbons selected from naphthalene, anthracene and phenanthrene.

Here, the content of the aromatic hydrocarbon is limited to 1% by weight or more, because if it is less than 1% by weight, the effect as the chemical shuttle cannot always be sufficiently obtained.

The present invention also provides a positive electrode (5) containing lithium.
And a negative electrode (6) made of a carbonaceous material capable of reversibly doping / dedoping lithium, and a non-aqueous electrolyte secondary battery (1), wherein the negative electrode is naphthalene. , Anthracene and phenanthrene are contained in an amount of 1 to 10% by weight of one or more aromatic hydrocarbons.

Here, the content of aromatic hydrocarbon is 1 to 1
The reason for limiting to 0% by weight is that if it is less than 1% by weight, the effect as a chemical shuttle is not always sufficiently obtained,
On the contrary, if it exceeds 10% by weight, the discharge capacity is lowered.

Note that the numbers in parentheses are for convenience of representing corresponding elements in the drawings, and the present invention is not limited to the description in the drawings. The same applies to the column of “Claims”.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical sectional view showing an embodiment of a non-aqueous electrolyte secondary battery according to the present invention, and FIG. 2 is a schematic view showing the action of aromatic hydrocarbons in an overcharged state.

A spiral type lithium secondary battery 1 which is a non-aqueous electrolyte secondary battery according to the present invention is as shown in FIG.
It has a bottomed cylindrical negative electrode can 2, and in the negative electrode can 2,
An electrode group 3 in which a positive electrode 5 containing lithium and a negative electrode 6 made of a carbonaceous material are spirally wound via a separator 7 is inserted. Further, the negative electrode can 2 is impregnated with a non-aqueous electrolytic solution, and the opening 12 of the negative electrode can 2 is provided with a sealing body 12 made of a positive electrode cup 13, a laminate film 14 and a positive electrode terminal 15, which is an insulating sealing gasket 10. Is fitted through. Further, a positive electrode lead plate 16 is provided between the positive electrode 5 and the positive electrode cup 13 so as to electrically connect both, and a negative electrode lead plate 17 is provided between the negative electrode 6 and the negative electrode can 2. It is provided so as to be electrically connected.

Here, the material of the positive electrode 5 may be any material as long as it contains lithium, for example, L.
iMn ₂ O ₄ and general formula LiMO ₂ (where M is Co, N
represents at least one of i. Therefore, a composite metal oxide represented by LiCoO ₂ , LiCo _0.8 Ni _0.2 O ₂ or the like) or an intercalation compound containing lithium is suitable.

Further, as the carbonaceous material of the negative electrode 6,
Any carbonaceous material may be used as long as it can reversibly dope and dedope lithium, but, for example, pyrolytic carbons, cokes (petroleum coke,
Pitch coke), natural graphite, glassy carbons, carbon blacks and the like.

The negative electrode 6 contains at least one kind of aromatic hydrocarbon selected from naphthalene, anthracene and phenanthrene. "One or more"
The term "includes cases where only one kind of naphthalene or the like is contained, cases where any two kinds are combined, and cases where all three kinds are contained.

The above non-aqueous electrolytic solution is prepared by appropriately combining an organic solvent and an electrolyte. Any of these organic solvents and electrolytes can be used as long as they are used in this type of battery. For example, as the organic solvent, propylene carbonate, ethylene carbonate, 1,
2-dimethoxyethane, 1,2-diethoxyethane, γ
-Butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane and the like, and electrolytes such as LiCoO ₄ and LiAsF
₆ , LiBF ₄ , LiJPF ₆ , LiCF ₃ SO ₃ , L
iCl and the like.

Since the spiral type lithium secondary battery 1 has the above-mentioned structure, as described below, it is necessary to prevent the spiral type lithium secondary battery 1 from bursting or igniting due to overcharge. You can

That is, when the spiral type lithium secondary battery 1 is overcharged and metal lithium is deposited on the surface of the negative electrode as much as possible, as shown in FIG. 2, the electrodeposited lithium and aromatic hydrocarbon are easily separated. As a result of the reaction, as shown by the arrow (a) in FIG. 2, a [lithium-aromatic hydrocarbon] complex is formed and eluted into the electrolytic solution. In FIG. 2, Ar is an aromatic hydrocarbon and Li [Ar] n is [lithium-aromatic hydrocarbon].
Represents a complex.

The [lithium-aromatic hydrocarbon] complex eluted in the electrolytic solution shows that the overcharged negative electrode is in a state in which lithium cannot be occluded any more. Since the positive electrode is anodically polarized at this time, an electrochemical reaction (a kind of short-circuit reaction) easily occurs with the positive electrode, and as shown by the arrow (b) in FIG. It will be calated and the aromatic hydrocarbon will be dissolved in the electrode liquid (Fig. 2).
Arrow (c)).

However, since the positive electrode is in an overcharged state, intercalated lithium is promptly deintercalated, and as shown by the arrow (d) in FIG.
Metal lithium is again electrodeposited on the negative electrode.

At this time, since the aromatic hydrocarbon is already dissolved in the electrolytic solution (step (c)), the lithium metal electrodeposited on the negative electrode and the aromatic hydrocarbon (arrow ( e)) or the unreacted aromatic hydrocarbon contained in the negative electrode reacts (arrow (f) step) to form a [lithium-aromatic hydrocarbon] complex again.

The aromatic hydrocarbon contained in the negative electrode is overcharged by repeating the above cycle of (a) → (b) → (c) → (d) → (e) or (f). It sometimes acts as a kind of chemical shuttle to suppress the growth of electrodeposited lithium on the negative electrode and prevent the solvent decomposition reaction here by supplying lithium to the positive electrode.

Although the spiral lithium secondary battery 1 has been described in the above embodiment, the present invention can of course be applied to a flat secondary battery such as a coin battery.

[0028]

Embodiments of the present invention will be described below. FIG. 3 is a graph showing the results of the discharge performance test of the non-aqueous electrolyte secondary battery, and FIG. 4 is a graph showing the results of the safety performance test of the non-aqueous electrolyte secondary battery.

<Preparation of Positive Electrode> LiCoO _{2 as a} positive electrode active material
And carbon powder as a conductive material and an aqueous dispersion of polytetrafluoroethylene (hereinafter abbreviated as PTFE) as a binder at a weight ratio of 100: 10: 10, and kneaded into a paste with water. The obtained product was applied to both sides of an aluminum foil having a thickness of 30 μm, dried, rolled, and cut into a predetermined size to produce a strip-shaped positive electrode sheet. The positive electrode active material LiCoO ₂ is cobalt oxide (Co
O) and lithium carbonate (Li ₂ CO ₃ ) in a molar ratio of 2: 1
And the mixture was heated in air at 900 ° C. for 9 hours. In addition, the ratio of the aqueous dispersion of PTFE in the mixing ratio of the above materials is the ratio of the solid content.

A part of the mixture of the positive electrode sheet was scraped perpendicularly to the longitudinal direction of the sheet, and a positive electrode lead plate made of titanium was spot-welded and attached on the current collector.

<Preparation of Negative Electrode> A commercially available coal-based pitch coke powder and an aqueous dispersion of PTFE as a binder were kneaded in a weight ratio of 100: 5, and the mixture was pressed into a nickel expanded metal and dried. After that, it was cut into a predetermined size to produce a strip-shaped negative electrode sheet. In addition, PT
The ratio of FE is the ratio of solid content as in the positive electrode.

Further, to contain an aromatic hydrocarbon,
The carbonaceous material was mixed at various ratios and kneaded by the same method to complete a negative electrode sheet.

A part of the mixture of the negative electrode sheet was scraped perpendicularly to the longitudinal direction of the sheet, and a nickel negative electrode lead plate was spot-welded and attached on the current collector.

<Assembly of Battery> These positive electrode and negative electrode were spirally wound with a polypropylene porous film separator interposed therebetween and inserted into a negative electrode can. Then, the positive electrode lead plate was spot-welded to a stainless steel positive electrode cup, and the negative electrode lead plate was spot-welded to the center position of the circular bottom surface of the negative electrode can.

Next, 2.3 ml of the non-aqueous electrolytic solution is injected into the negative electrode can, and then the sealing body is fitted into the negative electrode can and sealed. The non-aqueous electrolytic solution was prepared by mixing LiPF ₆ in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1.
What was melt | dissolved so that it might become mol / l was used.

The size of the completed battery is AA type (14.5φmm
× 50 mm).

<Discharge Performance Test> In order to compare the discharge performance of the batteries thus manufactured, a constant current / constant voltage charge of 400 mA was performed for 3 hours with an upper limit voltage of 4.2 V and a lower limit voltage of 2.5 V, and discharge was 400 mA. Was performed at a constant current of. Such a charge / discharge cycle is repeated up to 20 cycles,
The discharge capacity at the cycle was measured, and the effect of the added amount of aromatic hydrocarbons on the discharge capacity was investigated. The results are shown graphically in FIG. The discharge characteristics depended only on the amount of aromatic hydrocarbon added, and did not depend on the type of aromatic hydrocarbon.

As is clear from FIG. 3, the discharge capacity decreases as the amount of aromatic hydrocarbon added increases, and the discharge capacity decreases by 10% by weight.
It can be seen that the discharge capacity rapidly decreases when the value exceeds. It is considered that this is because the addition of aromatic hydrocarbons deteriorated the conductivity of the negative electrode, increased the internal resistance of the battery, and deteriorated the load characteristics. However, if the addition amount of the aromatic hydrocarbon is 10% by weight or less, the reduction rate of the discharge capacity is small (within about 10% when not added), and there is no practical problem.

<Safety Performance Test> Next, in order to compare the safety performance of these batteries, the batteries after 20 cycles were charged again with a constant current of 400 mA to artificially create an overcharged state, and after 2 hours. While measuring the voltage reached by
The overcharged state was maintained until after an hour.

As a result, in the battery containing less than 1% by weight of the aromatic hydrocarbon, as shown in FIG. 4, the ultimate voltage after 2 hours rapidly increased, and all of them burst or ignite within 3 hours. Came to. When these batteries were disassembled, a large amount of lithium was electrodeposited in all the batteries.

On the other hand, in the battery in which the amount of aromatic hydrocarbon added is 1% by weight or more, as shown in FIG. 4, the ultimate voltage after 2 hours is almost unchanged and overcharge is performed for 3 hours or more. However, it did not rise above 5.1V. This supports that the decomposition reaction of the electrolytic solution and the active material is suppressed.

This safety characteristic depends only on the amount of aromatic hydrocarbon added, not on the type of aromatic hydrocarbon.

[0043]

As described above, according to the present invention, the positive electrode 5 containing lithium, the negative electrode 6 made of a carbonaceous material capable of reversibly doping / dedoping lithium, and the non-aqueous electrolytic solution are provided. In the non-aqueous electrolyte secondary battery such as the spiral type lithium secondary battery 1 provided with, the negative electrode 6 is naphthalene,
Since it is configured to contain 1% by weight or more of one or more kinds of aromatic hydrocarbons selected from anthracene and phenanthrene, the aromatic hydrocarbons in the negative electrode 6 reversibly react with lithium metal during overcharge. By acting as a kind of chemical shuttle, the growth of electrodeposited lithium on the negative electrode 6 can be suppressed and the decomposition reaction of the electrolytic solution can be prevented by supplying lithium to the positive electrode 5.
Therefore, it is possible to avoid the risk of internal short circuit of the non-aqueous electrolyte secondary battery during overcharge and explosion / ignition due to this, and to improve the safety of this type of non-aqueous electrolyte secondary battery. It is possible to dramatically improve.

Further, according to the present invention, a spiral lithium battery including a positive electrode 5 containing lithium, a negative electrode 6 made of a carbonaceous material capable of reversibly doping and dedoping lithium, and a non-aqueous electrolyte solution. In the non-aqueous electrolyte secondary battery such as the secondary battery 1, the negative electrode 6 is configured to contain 1 to 10% by weight of one or more kinds of aromatic hydrocarbons selected from naphthalene, anthracene and phenanthrene. Therefore, it is possible to achieve the above-mentioned effect without lowering the discharge capacity.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a schematic diagram showing the action of aromatic hydrocarbons in an overcharged state.

FIG. 3 is a graph showing the results of a discharge performance test of a non-aqueous electrolyte secondary battery.

FIG. 4 is a graph showing the results of a safety performance test of a non-aqueous electrolyte secondary battery.

[Explanation of symbols]

1 ... Nonaqueous electrolyte secondary battery (spiral type lithium secondary battery) 5 ... Positive electrode 6 ... Negative electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiro Harada 5-311, Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Hidenori Nagura 5-36-11 Shinbashi, Minato-ku, Tokyo Fuji Electrochemical Co., Ltd.

Claims (2)

[Claims] 1. A non-aqueous electrolyte solution comprising a positive electrode (5) containing lithium, a negative electrode (6) made of a carbonaceous material capable of reversibly doping and dedoping lithium, and a non-aqueous electrolyte solution. In the secondary battery (1), the negative electrode contains one or more kinds of aromatic hydrocarbons selected from naphthalene, anthracene, and phenanthrene.
A non-aqueous electrolyte secondary battery, characterized by containing at least wt%. 2. A non-aqueous electrolyte solution comprising a positive electrode (5) containing lithium, a negative electrode (6) made of a carbonaceous material capable of reversibly doping and dedoping lithium, and a non-aqueous electrolyte solution. In the secondary battery (1), the negative electrode contains one or more kinds of aromatic hydrocarbons selected from naphthalene, anthracene, and phenanthrene.
A non-aqueous electrolyte secondary battery containing 10 to 10% by weight.