JPH0620721A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To provide a negative electrode and organic solvent-based electrolyte for a nonaqueous secondary battery of a favorable current efficiency and having a large capacity. CONSTITUTION:In a nonaqueous secondary battery comprising a positive electrode, organic solvent-based electrolyte, and a negative electrode, the negative electrode uses carbon material including graphite of a surface interval d002 of a carbon net surface of less than 0.337nm for active material, and the organic solvent-based electrolyte comprising gamma-BL and ring carbonate, and including i-butyrolactone at a ratio of 20 volume% or more and less than 50 volume% is used for the electrolyte. By combination of the negative electrode, the electrolyte, and various types of the positive electrodes, a nonaqueous secondary battery of a large current efficiency, and a large capacity can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high capacity non-aqueous secondary battery negative electrode and an electrolytic solution using an organic solvent as an electrolytic solution.

[0002]

It is known to use a carbonaceous material as a negative electrode of a non-aqueous secondary battery using an organic solvent as an electrolytic solution. The carbonaceous materials used as electrodes are roughly classified into the following three types based on their electrochemical properties. The first is the narrow spacing of carbon mesh planes represented by graphite (d ₀₀₂ <0.337n
m), a carbon net surface and a carbon surface grown in the laminating direction of the net surface. It is known that such a carbon material intercalates both cations and anions between the carbon network planes to form an intercalation compound, and is considered to be applied as a conductive material, an organic synthesis reaction catalyst or a battery. Has been. The use of graphite as the negative electrode of batteries is disclosed in JP-A-57-20.
No. 8079, No. 58-192266, No. 59-143280, and No. 60-5418.
No. 1, JP-A-60-182670, JP-A-6
No. 0-221973, Japanese Patent Application Laid-Open No. 61-7567, Japanese Patent Application Laid-Open No. 1-311565. In these patents, propylene carbonate (hereinafter abbreviated as PC), tetrahydrofuran (hereinafter abbreviated as THF), γ-butyrolactone (hereinafter abbreviated as γ-BL), 1,2-dimethoxyethane (hereinafter abbreviated as organic solvents that can be used in these patents. (Abbreviated as DME), sulfolane and the like. Examples include LiClO ₄ or Li
BF ₄ is used, and PC or THF is used as a typical solvent. Although it is described that a mixed solvent may be used, there is no description that the performance is particularly improved when the mixed solvent is used. An example using a mixed solvent is disclosed in JP-A-57-208079.
Only the PC / DME disclosed in the publication.

However, when LiClO ₄ or LiBF ₄ was used as the electrolyte and PC was used as the solvent, an attempt was made to charge and discharge with graphite, but almost no charge or discharge could be achieved. Also, using LiBF ₄ as an electrolyte, PC / DME which is a mixed solvent
An attempt was made to charge and discharge graphite by using graphite as an electrode, but it was found that the current efficiency was extremely low and it was not practical. Graphite has a high utilization rate (lithium storage amount per carbon) of 16.7% when intercalating lithium ions as cations, but when it is intended to be used as a negative electrode of a battery, it is electrochemically charged as described above. Cannot effectively absorb and release lithium. This is what the Journal of Electrochemical Society (J. Electroche
m. Soc. ) Volume 117, page 222 (1970)
Year) and Comparative Example 1 of JP-A-63-2555, an intercalation compound in which lithium ions are occluded in graphite has a high reactivity with an organic solvent and reacts with an electrolytic solution rather than acting as an electrode. Has priority, and its utility value as an electrode is low.

The second group is a group having a very large surface area (S _A > 100 m ² / g) typified by activated carbon, a large spacing between carbon mesh planes (d ₀₀₂ > 0.337 nm), and crystallization is not advanced. . Since this type has a large surface adsorption amount, the lithium storage amount per carbon is large, but the current efficiency is low and the cycleability is low. In the third group, the carbon net plane has grown to some extent, but the carbon net plane spacing is wider than that in the first group (d ₀₀₂ > 0.337 nm). This group shows various electrochemical characteristics depending on its structure, but unlike the first group, it can occlude lithium with almost no reaction with the electrolytic solution. However, the utilization rate (lithium storage amount per carbon) is smaller than that of the first group.

On the other hand, examples in which graphite is used as a negative electrode include US Pat. No. 4,423,125 and Journal of Electrochemical Society (J. Elec).
trochem. Soc. ) Volume 137, page 2009 (1990). US Patent 4423
In 125, dioxolane is used as the electrolytic solution. Dioxolane is chemically unstable, and also electrochemically at 3.5 V or higher, the electrolytic solution is polymerized and an active material having a high voltage cannot be used for the positive electrode, which is disadvantageous. Journal of Electrochemical Society (J. El
microchem. Soc. ) Volume 137, 2009
Page (1990) describes electrochemical lithium intercalation using graphite and petroleum coke as electrodes and a mixed solvent of PC and ethylene carbonate (hereinafter abbreviated as EC) as an electrolyte. In petroleum coke, the side reaction that occurs during the first charge depends on the surface area, whereas in graphite, a side reaction that does not depend on the surface area occurs in addition to the side reaction that depends on the surface area during the first charge. Have been described. When a battery is assembled in such a system, a large number of positive electrodes are required because the initial current efficiency is low, and it is difficult to increase the capacity because the utilization rate of the positive electrode as a battery per active material cannot be increased. . Therefore, in order to increase the capacity, both the positive electrode and the negative electrode are in a charged state (the negative electrode carbon absorbs lithium,
The positive electrode may be assembled with the lithium receiving site being empty), but the electrode in the charged state is extremely reactive and may cause a safety problem or may be inactive. It is not practical because it requires complicated steps such as assembling the battery under gas. Further, it is described that in the system of this report, a side reaction occurs continuously after 2 cycles and the current efficiency does not reach 100%. High current efficiency is especially important for battery cycleability. In order to discharge a certain capacity when the current efficiency of the negative electrode is low, the positive electrode always needs to have a charge amount equal to or larger than the discharge capacity. Bring Also, if the positive electrode is charged with a constant capacity so that the positive electrode does not become overcharged,
Since the current efficiency is low, repeating the cycle causes a decrease in capacity.

In any case, in order to obtain a secondary battery having a high capacity and good cycle characteristics, what is required for the negative electrode is that the electrode is stable during assembly, the current efficiency is high, and the utilization rate is high. In the conventional electrolyte system, the first group of carbonaceous materials reacts with the electrolyte, so the second group has low current efficiency, so the utility value is low, and the third group has some current efficiency. However, in this case as well, the utilization factor (the amount of stored lithium per carbon atom) is about 10%, and in order to increase the capacity of the battery, a negative electrode material having a higher utilization factor and good current efficiency has been desired.

[0007]

The object of the present invention is to combine a specific organic solvent electrolyte having a high utilization factor, a high current efficiency and an excellent cycle property for the purpose of increasing the capacity of a secondary battery. It is to provide a negative electrode.

[0008]

In order to solve the above-mentioned problems, the inventors of the present invention have diligently studied a combination of a carbonaceous material used for a negative electrode and an organic solvent electrolyte solution, and found that a large amount of lithium ion However, when it is used as a negative electrode of a battery, graphite which is said to be unable to be effectively charged and discharged due to the reaction with an electrolytic solution is γ-B.
L and cyclic carbonates, and the γ-BL content is 2
Unexpectedly, when an electrolyte solution of 0% by volume or more and less than 50% by volume is used, the capacity for charging and discharging is large,
Moreover, they have found that the current efficiency is also high, and have completed the present invention. That is, the present invention relates to (1) a non-aqueous secondary battery comprising a chargeable / dischargeable positive electrode, an organic solvent-based electrolytic solution, and a negative electrode whose main active material is a carbonaceous material, and the carbonaceous material of the negative electrode active material is a carbon mesh. Containing graphite having a surface spacing d ₀₀₂ of less than 0.337 nm and an organic solvent-based electrolyte mainly composed of γ-BL and a cyclic carbonate, and the γ-butyrolactone content is 20% by volume or more and 5% or more.
Non-aqueous secondary battery characterized by less than 0% by volume (2) The above non-aqueous secondary battery using a transition metal chalcogen compound containing lithium as a positive electrode (3) Both the positive electrode and the negative electrode are in a discharged state during battery assembly The above non-aqueous secondary battery is provided.

The present invention will be described in detail below. The graphite having a carbon mesh plane spacing d ₀₀₂ of less than 0.337 nm as used in the present invention means a carbonaceous material in which carbon mesh planes are regularly laminated, such as graphite. The carbonaceous material has various structures depending on its starting material and its treatment (manufacturing) method. However, in any material, the interplanar spacing d ₀₀₂ of the carbon mesh plane becomes small due to the high temperature treatment, and the laminated thickness Lc of the carbon mesh plane is Graphite tends to be large, and graphite has the smallest facet spacing d ₀₀₂ = 0.3354 nm. The decrease of d ₀₀₂ and the increase of Lc greatly differ depending on the carbonaceous material, and easily graphitized carbon easily graphitized by high temperature treatment (up to 3000 ° C.) and difficult graphitization to progress (d ₀₀₂ does not easily become small). Classified as graphitized carbon. When graphitizing this carbonaceous material, d
_In addition to ₀₀₂ and Lc, the density, surface area, electric resistance, etc. also change greatly, but the interplanar spacing is particularly important for the formation of the intercalation compound.

The carbonaceous material of the present invention has a d ₀₀₂ of 0.337.
Those of less than nm are particularly effective, and d ₀₀₂ is 0.337.
If the thickness is more than nm, the current efficiency becomes low and the amount of lithium stored per carbon (utilization rate) becomes low, which is not preferable. In addition, although the current efficiency may be somewhat lowered, the negative electrode of the present invention can be produced by using the graphite in combination with another carbonaceous material. For example, coke as such a carbonaceous material is used. , Acetylene black, activated carbon, mesophase microbeads, needle coke and the like.

D ₀₀₂ used in the present invention is 0.337n
The graphite having a size of less than m is not particularly limited as a starting material, but it is generally obtained by heat-treating petroleum pitch, coal tar pitch, pyrolytic carbon, needle coke, condensed polycyclic hydrocarbon, etc. at 2500 ° C. or higher, more preferably 3000 ° C. or higher. can get. Also, naturally occurring graphite can be used in the present invention.

The lamination thickness Lc of the carbon network surface of graphite used in the present invention is not particularly limited, but Lc is also an important parameter for graphitization, and preferably 30n.
m or more, and more preferably 50 nm or more. 30 nm
If it is less than, the utilization rate tends to be low. The surface area is also not particularly limited, but if the surface area is large, many side reactions are likely to occur, so it is preferably 50 m ² / g or less, more preferably 20 m ² / g or less.

The shape of the graphite used in the present invention may be powdery or fibrous, and is not particularly limited, but powdery is preferably used because the packing density is easily increased. A powder having a particle diameter of 0.1 to 50 μm, preferably 1 to 50 μm is suitably used. The electrolytic solution of the present invention is γ
It is essential to contain -BL in an amount of 20% by volume or more and less than 50% by volume. If it is less than 20% by volume, the current efficiency is low, and if it is 50% by volume or more, the output characteristics after a long-term charge / discharge cycle are inferior. When the content is less than 20% by volume, the reaction between the lithium-containing graphite and the solvent of the second component has priority over lithium intercalation (charging reaction), the current efficiency is low, and the utilization rate is also low. Also, 5
At 0% by volume or more, the current efficiency is good, but when charging and discharging are repeated, a slight reaction of γ-BL itself occurs and the output characteristics after a long-term charging / discharging cycle deteriorate, probably due to electrolyte deterioration. On the other hand, γ-BL is 20% by volume or more and 50% by volume
In the case of the electrolytic solution of the present invention containing less than the above, the reaction with the graphite is suppressed, the current efficiency and the utilization rate are increased, and the output characteristics after a long-term charge / discharge cycle are excellent.

The graphite of the present invention is used as a negative electrode, and P containing an electrolyte is used.
In the C-only solvent-based electrolyte, graphite cannot be charged because the graphite expands and falls off from the electrode as PC decomposes. When γ-BL is added to this PC system, decomposition of PC and expansion of graphite are suppressed and charging becomes possible. The organic solvent cyclic carbonates combined with γ-BL include EC,
Examples include PCs. Further, these may be mixed and used.

Organic solvents other than γ-BL and cyclic carbonates, for example, ethers, ketones, carbonates, nitriles, amides, sulfone compounds, esters, aromatic hydrocarbons and the like are added in small amounts. Good. Further, these may be used in combination. Among these, ethers, ketones, nitriles, esters and the like are preferable.

As a specific example, dimethoxyethane (DM
E), tetrahydrofuran (THF), 2-methyl-tetrahydrofuran, anisole, 1,4-dioxane,
4-methyl-2-pentanone, cyclohexane, acetonitrile, propionitrile, butyronitrile, butylene carbonate, diethyl carbonate (hereinafter abbreviated as DEC) dimethylformamide, dimethylacetamide, dimethylsulfoxide, sulfolane, methyl formate,
Ethyl formate, methyl acetate, ethyl acetate, propyl acetate,
Examples thereof include ethyl propionate.

As a positive electrode combined with the negative electrode of the present invention
Is not particularly limited, but MnO₂, MoO₃,
V₂O_Five, V₆O₁₃, Fe₂O₃, Fe₃O_Four, Richiu
Mum-containing transition metal chalcogen compound, Li_(1-X)Co
O₂, Li_(1-X)・ NiO₂, TiS₂, MoS₃, F
eS₂, CuF₂, NiF₂Inorganic compounds such as
Carbon, graphite, vapor grown carbon fiber and / or
Pulverized carbon fiber and / or pulverized product thereof
Carbon materials such as polyacetylene, poly-p-phenylene
Conductive polymers such as Does not contain lithium
For the positive electrode, use the negative electrode of the present invention to occlude lithium.
Or the required amount of metallic lithium is added to the negative electrode of the present invention.
The battery can be contained by joining and using it. Only
However, such batteries should be assembled under inert gas during assembly.
As a result, the assembly process becomes complicated. Richi
When using transition metal chalcogen compounds containing um
Battery, both the positive and negative electrodes are assembled in a stable discharge state in air.
It can stand up, and there are few restrictions on processing and assembly.
Safe, with no risk of heat generation or explosion due to battery short circuit, etc.
It is also preferable from the above. Such a lithium-containing transition metal catalyst
Examples of the rucogen compound include Li_(1-X)Co
O₂, Li_(1-x)NiO₂, Li_(1-x)Co_(1-y)Ni
_yO₂LiMn₂O_Four, Li_(1-X)Co_(1-Y)M_YO₂
(M is a transition metal other than Co and Ni, Al, In, Sn, etc.
), Li_(1-X)A_ZCo_(1-Y)M_YO₂(A is L
Alkali metals other than i).

The electrolyte used in the present invention is not particularly limited, but LiBF ₄ , LiAsF ₆ and LiPF ₄ are used.
₆ , LiClO ₄ , CF ₃ SO ₃ Li, LiI, LiA
_{lCl 4, NaClO 4, NaBF 4} , NaI, (n-
Bu) ₄ NClO ₄ , (n-Bu) ₄ NBF ₄ , KPF
_{6 and the} like are used. Among them, LiBF ₄ , LiPF ₆ are used from the viewpoint of battery performance, handling safety and toxicity.
Is preferred.

Further, when an electrode is formed using the graphite of the present invention, a current collector, a mixture or the like may be used. Cu, Ni or the like is used as the current collector, and Teflon is used as the mixture.
Polymers such as polyethylene, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose and acrylonitrile, vinyl fluoride, vinylidene fluoride and chloroprene are used. Further, as a method for forming this electrode, a method of mixing an electrode active material and an organic polymer, compression molding, a method of dispersing the electrode active material in a solvent solution of the organic polymer, followed by coating and drying, an aqueous solution of the organic polymer. Alternatively, a method of coating and drying after dispersing the electrode active material in the oily dispersion is known, but it is not particularly limited. A method of dispersing the electrode active material in the combined aqueous or oily dispersion and then coating and drying, more preferably, a non-fluorine-containing organic polymer containing particles of 0.5 μm or less in the organic polymer is preferably used.

If necessary, components such as a separator, a terminal and an insulating plate are used as the constituent elements of the battery.

[0021]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the invention is not limited thereto. Further, in Examples 1 to 4 and Comparative Examples 1 to 2, metallic lithium was used as the counter electrode in order to see the performance of the negative electrode alone. In this case, the carbonaceous negative electrode conventionally becomes the positive electrode, but since it receives lithium ions during discharge and is reduced, it is referred to as the negative electrode and the reduction direction is referred to as charging. The quantity / charged quantity of electricity, the utilization rate is the quantity of discharged electricity / the quantity of electricity per weight of the negative electrode active material (12 g is 96485 coulomb), and the numbers indicate the number of cycles.

[0022]

Example 1 Graphite (SP10 manufactured by Nippon Graphite Co., Ltd.,
d ₀₀₂ = 0.3355 nm, Lc> 100 nm, BET surface area by adsorption of N ₂ = 13 m ² / g) 100 parts by weight of styrene / butadiene latex (Asahi Kasei Corporation)
Manufactured by L1571 (solid content 48% by weight) 4.17 parts by weight, carboxymethylcellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd. BSH12) aqueous solution (solid content 1% by weight) 1 as a thickener 1
30 parts by weight and 30 parts by weight of water were added and mixed to obtain a coating liquid. This coating liquid was applied and dried using a 10 μCu foil as a base material to obtain a negative electrode having a thickness of 100 μ and 95 g / m ² .
The negative electrode was peeled off leaving a portion of 1 cm × 1 cm to obtain a working electrode shown in FIG. On the other hand, as the counter electrode, a metal lithium-bonded SUS net was used, and as the reference electrode, metal lithium was used. 1 M LiBF ₄ was added to the electrolytic solution of the above electrodes in an Ar gas atmosphere with γ-BL + PC (volume ratio 25:
75) The battery shown in FIG. 1 was assembled using the electrolytic solution dissolved in the mixed solvent. This battery was repeatedly charged with a constant voltage of 1 mA to 10 mV and discharged with a constant current of 1 mA to 1 V. Table 1 shows the current efficiency and utilization rate in the charge / discharge cycle of this battery.

[0023]

[Example 2] γ-BL + PC (volume:
(Ratio 25:75) γ-BL + EC (volume
Product ratio 45:55), 1M LiBF_FourInstead of 1MLi
PF ₆Was performed in the same manner as in Example 1 except that was used. The result
It shows in Table 1.

[0024]

Example 3 Instead of a mixed solvent of γ-BL + PC (volume ratio 25:75) as a solvent of an electrolytic solution, γ-BL + PC + E
Example 1 except that C (volume ratio 30:35:35) was used
I went the same way. The results are shown in Table 1.

[0025]

Example 4 γ-BL + EC + D instead of γ-BL + PC (volume ratio 25:75) mixed solvent as the solvent for the electrolytic solution
Example 1 was repeated except that ME (volume ratio 45:45:10) was used. The results are shown in Table 1.

[0026]

Comparative Example 1 The same procedure as in Example 1 was carried out except that PC was used instead of the γ-BL + PC (volume ratio 25:75) mixed solvent as the solvent for the electrolytic solution. When energization was started, graphite was expanded and dropped from the Cu foil with the generation of bubbles due to decomposition of PC, and charging could not be performed.

[0027]

Comparative Example 2 γ-BL + PC as a solvent as an electrolyte
(Volume ratio 25:75) γ-BL + P instead of mixed solvent
Example 1 was repeated except that C (volume ratio 10:90) was used. The results are shown in Table 1. Example 4 shows an example of a battery in which a lithium-containing chalcogen compound is combined as the positive electrode.

[0028]

Example 5 100 parts by weight of LiCoSn _0.02 O ₂ having a particle size of 3 μ was used as a conductive filler for graphite (Lon.
20 parts by weight of KS6 (trade name: KS6) and 100 parts by weight of a 5% dimethylformamide solution of poly (fuccavinylidene) as a binder were added and mixed to obtain a coating solution. 15 μAl
This coating liquid is applied to a foil as a base material and dried to give a thickness of 120.
A positive electrode with μ, 290 g / m ² was obtained. The above positive electrode and the negative electrode (95 g / m ² ) obtained in Example 1 were cut into 1 cm × 1 cm, and the battery shown in FIG. 2 was assembled. 1M for electrolyte
LiBF ₄ was added to γ-BL + PC + EC (volume ratio 30: 3
5:35) was used. This battery was repeatedly charged at a constant voltage of 5 mA to 4.2 V and discharged at a constant current of 5 mA to 2.7 V. The current efficiency and utilization rate during the first cycle charging / discharging of this battery were 85.0 each.
% And 15.8%. Further, the current efficiency and the utilization rate in the 10th cycle of charging and discharging are 99.6 respectively.
% And 15.6%. The discharge capacity at the 100th cycle retained 90% of the discharge capacity at the 1st cycle.

[0029]

[Table 1]

[0030]

EFFECT OF THE INVENTION Negative electrode of the present invention (spacing of carbon mesh surface d ₀₀₂
A carbonaceous material containing a graphite of less than 0.337 nm)
A combination of an electrolytic solution mainly composed of γ-BL and cyclic carbonates and having a γ-butyrolactone content of 20% by volume or more and less than 50% by volume and various positive electrodes, the current efficiency is large and the capacity is large. An aqueous secondary battery can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a configuration example of a battery of the present invention.

FIG. 2 is a cross-sectional view of a configuration example of the battery of the present invention.

[Explanation of symbols]

 1 Working electrode (carbonaceous negative electrode) 2 Counter electrode (metallic lithium) 3 Reference electrode (metallic lithium) 4 Electrolyte solution 5 Glass container 6 Ar gas 7 Positive electrode 8 Negative electrode 9 Current collecting rod 10 Current collecting rod 11 SUS net 12 SUS net 13 External electrode terminal 14 external electrode terminal 15 battery case 16 separator 17 electrolyte

Claims (1)

[Claims] 1. A non-aqueous secondary battery comprising a chargeable / dischargeable positive electrode, an organic solvent-based electrolytic solution, and a negative electrode mainly containing a carbonaceous material as an active material, wherein the carbonaceous material of the negative electrode active material is a carbon mesh surface. The spacing d ₀₀₂ contains a graphite having a size of less than 0.337 nm, the organic solvent-based electrolyte is mainly composed of γ-butyrolactone and cyclic carbonates, and the γ-butyrolactone content is 20% by volume or more and less than 50% by volume. Non-aqueous secondary battery characterized in that