JPH1145724A - Nonaqueous electrolytic battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain self-discharge and improve a storage characteristic, by providing a positive electrode, a negative electrode made of lithium or material which can store and discharge lithium, and a nonaqueous electrolyte which consists of an organic solvent containing a specific amount of dioxolane, α- pyrolidone, etc., and solute. SOLUTION: By storing a positive electrode 7 made of MnO2 , etc., a negative electrode 1 made of lithium or graphite which can store and discharge lithium, and a separator 8 impregnated with a nonaqueous electrolyte between them in a negative electrode can 3, positive electrode can 5, and an insulating packing 4 through a negative electrode current collector 2 and a positive electrode current collector 6, a nonaqueous electrolytic battery is provided. The electrolyte is composed of an organic solvent such as ethylene carbonate containing more than 10 wt.% of dioxolane and solute such as LiPF6 . By adding 0.01-30.0% of an additive such as α-pyrolidone, β-pyrolidone, imidazoline, succinimide, maleimide, and derivative of them, a storage characteristic is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonaqueous electrolyte battery using lithium as a negative electrode active material, that is, to an improvement in the storage characteristics of a lithium battery.

[0002]

2. Description of the Related Art A lithium battery using, for example, lithium as a negative electrode active material has attracted attention as a high energy density battery, and has been actively studied.

[0003] In general, in this type of battery, as a solvent constituting a non-aqueous electrolytic solution, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, sulfolane, 1,2-dimethoxyethane, tetrahydrofuran, dioxolane, etc. Binary or ternary mixtures have been used.
LiPF ₆ , LiB
F ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiA _S F ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiCF
₃ (CF ₂ ) ₃ SO _{3 and the} like can be listed.

By the way, dioxolane alone or a binary or ternary mixed solvent containing dioxolane,
In addition, the non-aqueous electrolytic solution composed of a solute and a solute has a problem in that the negative electrode using an organic solvent and lithium as an active material causes a chemical reaction, so that the battery capacity after storage is reduced. Therefore, suppressing self-discharge during storage is an important issue in putting this type of battery to practical use.

For example, as disclosed in JP-A-49-108525, there is a method in which pyridine is added to an electrolytic solution in order to improve storage characteristics. In this method, an organic solvent containing dioxolane is also used. In the case of a battery using, sufficient characteristics have not yet been obtained, and there is room for improvement.

[0006]

SUMMARY OF THE INVENTION The present invention proposes an excellent non-aqueous electrolyte which suppresses self-discharge when the battery is stored and improves storage characteristics.

[0007]

The present invention comprises a positive electrode, a negative electrode comprising lithium or a negative electrode material capable of inserting and extracting lithium, and a non-aqueous electrolyte comprising an organic solvent containing dioxolane and a solute. In the non-aqueous electrolyte battery, the dioxolane is contained in an amount of 10% by weight or more based on the organic solvent, and the organic solvent comprises α-pyrrolidone, β-pyrrolidone, imidazolidone, succinimide, maleimide and derivatives thereof. Characterized by containing at least one additive selected from the group consisting of: The reason is that dioxolane is 10% by weight
When a non-aqueous electrolytic solution to which the above-mentioned organic solvent is added with α-pyrrolidone, β-pyrrolidone, imidazolidone, imidazolidone, succinimide, maleimide and one of their derivatives as additives, the presence of a specific amount of dioxolane Then, the additive reacts with lithium to form a good-quality film on the negative electrode. It is considered that this coating suppresses the direct contact between lithium and the solvent, thereby suppressing the decomposition of the non-aqueous electrolyte due to the contact between lithium and the electrolyte. In this way, the storage characteristics of the battery can be improved.

Here, the structural formula of α-pyrrolidone is shown in Chemical formula 1.

[0009]

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## STR2 ## The chemical formula of β-pyrrolidone is shown below.

[0011]

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Formula 3 shows the structural formula of imidazolidone.

[0013]

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Formula 4 shows the structural formula of succinimide.

[0015]

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Formula 5 shows the structural formula of maleimide.

[0017]

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In the above additive, the derivative of α-pyrrolidone means that at least one hydrogen atom bonded to a carbon atom of α-pyrrolidone is converted to —CH ₃ (methyl group), —C ₂ H ₅ (ethyl group) or Halogen atom (fluorine F, chlorine Cl)
Is replaced by In addition, β-pyrrolidone derivatives, imidazolidone derivatives, succinimide derivatives, maleimide derivatives, similarly, at least one hydrogen atom bonded to the carbon atom constituting each compound,
It is one substituted with -CH ₃ (methyl group), -C ₂ H ₅ (ethyl group) or a halogen atom (fluorine F, chlorine Cl).

Among the above additives, α-pyrrolidone, β-pyrrolidone
Pyrrolidone and imidazolidone and their derivatives are
It is considered that it is easy to form an optimal film on the negative electrode or it is easy to be adsorbed on the negative electrode, which is preferable. The reason is that
Is presumed to be because the structure represented by is easy to approach and react with lithium, or because the electron distribution of each structure has a form that easily reacts with lithium metal. Is done. Among them, imidazolidone and its derivatives can further suppress the self-discharge rate.

The amount of the additive is preferably 0.01% by weight or more and 30.0% by weight or less, more preferably 0.1% by weight to 20.0% by weight, based on the weight of the organic solvent. However, this type of nonaqueous electrolyte battery is suitable from the viewpoint of suppressing a decrease in discharge capacity after storage.

The solutes of this type of battery include LiPF ₆ , LiB
F ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiA _S F ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂
F ₅ SO ₂ ) ₂ , LiCF ₃ (CF ₂ ) ₃ SO ₃ , LiC (CF ₃ SO ₂ ) _{3 and the} like can be used, but are not limited thereto.

As a solvent for this type of battery, dioxolane alone or containing 10% by weight or more of dioxolane, and ethylene carbonate, propylene carbonate,
It is possible to use a mixture to which butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, sulfolane and tetrahydrofuran are added.

As the positive electrode of this type of battery, a metal oxide containing at least one of manganese, cobalt, nickel, vanadium, and niobium can be used, but is not limited thereto.

As the negative electrode of this type of battery, a substance capable of electrochemically absorbing and releasing lithium ions,
Alternatively, those using metallic lithium as an electrode material are exemplified.
Materials capable of electrochemically storing and releasing lithium ions include carbon materials such as graphite, coke, and fired organic materials, and lithium-aluminum alloys, lithium-magnesium alloys, lithium-indium alloys, and lithium-tin. Alloy, lithium-thallium alloy, lithium-
Examples thereof include lithium alloys such as a lead alloy and a lithium-bismuth alloy.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. (Experiment 1) FIG. 1 shows a half sectional view of a flat nonaqueous electrolyte battery as one embodiment of the present invention. A negative electrode 1 made of lithium metal is pressed on the inner surface of a negative electrode current collector 2, and the negative electrode current collector 2 is fixed to the inner bottom surface of a negative electrode can 3 having a U-shaped cross section made of ferritic stainless steel (SUS430). Have been. The peripheral end of the negative electrode can 3 is fixed inside an insulating packing 4 made of polypropylene, and the outer periphery of the insulating packing 4 is made of stainless steel and has a U-shaped cross section in a direction opposite to the negative electrode can 3. 5 is fixed. A positive electrode current collector 6 is fixed to the inner bottom surface of the positive electrode can 5,
A positive electrode 7 is fixed to the inner surface of the positive electrode current collector 6.
Between the positive electrode 7 and the negative electrode 1, a separator 8 impregnated with a non-aqueous electrolyte, which is a key point of the present invention, is interposed.

By the way, the positive electrode 7 uses manganese dioxide heat-treated at a temperature of 400 ° C. as an active material. The heat treatment can be changed in a temperature range from 350 to 430C. This manganese dioxide, carbon powder as a conductive agent, and fluororesin powder as a binder are mixed at a weight ratio of 85: 10: 5, respectively. Next, this mixture was subjected to pressure molding and then dried at 300 ° C. to produce a positive electrode 7. This drying process can be set and changed in a temperature range of 250 to 350 ° C.

On the other hand, the negative electrode 1 is produced by punching a rolled lithium plate into a predetermined size.

As the electrolytic solution, a mixed organic solvent of propylene carbonate (PC) and dioxolane (DOXL) (5 types by weight: 10: 0, 95: 5, 9: 1, 5: 5, 0:10)
In a solution of lithium trifluoromethanesulfonate as a solute at a ratio of 1 mol / l, α-pyrrolidone as an additive was added in an amount of 1.0% by weight based on the weight of the mixed organic solvent.
To obtain a non-aqueous electrolyte solution. Batteries A1 to A5 having an outer diameter of 20.0 mm and a thickness of 2.5 mm were produced using this non-aqueous electrolyte. (Experiment 2) B1 to B5 were produced in the same manner except that β-pyrrolidone was used as an additive in place of α-pyrrolidone used in Experiment 1. (Experiment 3) Batteries C1 to C5 were produced in the same manner except that imidazolidone was used as an additive instead of α-pyrrolidone used in Experiment 1. (Experiment 4) Batteries D1 to D5 were prepared in the same manner except that succinimide was used as an additive in place of α-pyrrolidone used in Experiment 1. (Experiment 5) Batteries E1 to E5 were produced in the same manner except that maleimide was used as an additive in place of α-pyrrolidone used in Experiment 1. (Experiment 6) Similar batteries were produced in Experiment 1 using an electrolyte solution to which α-pyrrolidone and the like were not added, and these were designated as batteries X1 to X5.

These batteries A1 to A5, B1 to B5, C1 to C5, D1
Using D5, E1 to E5, and X1 to X5, the storage characteristics of each battery were compared. The experimental conditions were as follows: After each battery was prepared and stored at 60 ° C. for 2 months, the battery was actually discharged and compared with the capacity before storage. Was determined. Table 1 shows the results.

[0030]

[Table 1]

From Table 1, it can be seen that the batteries A3 to A5, B3 to B
5, C3 to C5, D3 to D5 and E3 to E5 are comparative batteries A1, A2, B
1, B2, C1, C2, D1, D2, E1, E2 and X1 to X5,
It can be seen that the self-discharge rate is small and the decrease in battery capacity during storage is suppressed, and self-discharge is suppressed. (Experiment 7) A battery having the same configuration as the batteries A4, C4, and E4 in Experiment 1 was prepared, and the amounts of α-pyrrolidone, imidazolidone, and maleimide added to the non-aqueous electrolyte were changed, and after storage. Of the batteries were compared. Under these experimental conditions, each battery was prepared and stored at 60 ° C. for 2 months, and the discharge capacity (mAh) of the battery was measured.

Table 2 shows the results. Table 2 shows that α-pyrrolidone, imidazolidone,
It shows the relationship between the amount of maleimide added and the self-discharge rate (%). Note that the calculation of the self-discharge rate is based on Experiment 1 described above.
Same as 6.

[0033]

[Table 2]

From these results, the effect of adding α-pyrrolidone, imidazolidone and maleimide in the range of 0.01% by weight to 30.0% by weight based on the weight of the organic solvent was observed, and the battery capacity after storage was reduced. Has been suppressed. The addition amount is preferably in the range of 0.1% by weight to 20.0% by weight from the viewpoint of not lowering the discharge capacity of the battery after storage.

In Experiment 7, the amounts of α-pyrrolidone, imidazolidone and maleimide were changed, but other additives, ie, derivatives of the above additives, β-pyrrolidone,
A similar tendency is observed in batteries using succinimide.

In each of the above embodiments, the non-aqueous electrolyte
As a solute to be dissolved, trifluoromethanesulfonic acid
Titanium LiCF_ThreeSO_ThreeBut LiPF₆, LiClO_Four, LiBF_Four, Li
N (CF _ThreeSO_Two)_Two, LiN (C_TwoF_FiveSO_Two)_Two, LiC (CF_ThreeSO_Three)_Three, LiCF_Three(C
F_Two)_ThreeSO_Three, LiAsF₆It goes without saying that can be used. Ma
Propylene carbonate and dioxo as organic solvents
As an example of a mixed solvent of orchid, dioxolane is 10% by weight.
Containing butylene carbonate, vinyleneca
-Carbonate, dimethyl carbonate, diethyl carbonate
, Ethyl methyl carbonate, tetrahydrofuran
Can be used.

[0037]

As described above, by adding at least one of the additives α-pyrrolidone, β-pyrrolidone, imidazolidone, succinimide, maleimide and derivatives thereof to the non-aqueous electrolyte solution, The storage characteristics of the battery can be improved. And, in particular,
As the additive, α-pyrrolidone, β-pyrrolidone,
One of the imidazolidones is suitable, among which imidazolidone is particularly suitable. Further, regarding the amount of the additive, 0.011 weight
A suitable range is from 0.1% to 30.0% by weight, especially from 0.1% by weight.
When the content is in the range of 20.0% by weight, the storage characteristics of the battery can be significantly improved, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a battery of the present invention.

[Explanation of symbols]

 Reference Signs List 1 negative electrode 2 negative electrode current collector 3 negative electrode can 4 insulating packing 5 positive electrode can 6 positive electrode current collector 7 positive electrode 8 separator

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (5)

[Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode comprising lithium or a negative electrode material capable of inserting and extracting lithium, and a non-aqueous electrolyte comprising an organic solvent containing dioxolane and a solute. The dioxolane is contained in an amount of 10% by weight or more based on the organic solvent, and the organic solvent is α-pyrrolidone;
A non-aqueous electrolyte battery comprising at least one additive selected from the group consisting of β-pyrrolidone, imidazolidone, succinimide, maleimide, and derivatives thereof. 2. The non-aqueous system according to claim 1, wherein the additive is at least one additive selected from the group consisting of α-pyrrolidone, β-pyrrolidone, imidazolidone and derivatives thereof. Electrolyte battery. 3. The non-aqueous electrolyte battery according to claim 2, wherein the additive is at least one additive selected from the group consisting of imidazolidone and a derivative thereof. 4. The non-aqueous electrolyte battery according to claim 1, wherein the amount of the additive ranges from 0.01% by weight to 30.0% by weight based on the organic solvent. 5. The non-aqueous electrolyte battery according to claim 4, wherein the amount of the additive ranges from 0.1% by weight to 20.0% by weight based on the organic solvent.