JPH08167426A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: To obtain a lithim secondary battery having large energy density by improving charge and discharge efficiency of a negative electrode in the initial stage of a cycle. CONSTITUTION: A lithium secondary battery is composed of a negative electrode using one kind or two or more kinds selected from a group composed of a carbon material capable of electrochemically storing and releasing a lithium ion as an active material, a positive electrode capable of storing and releasing a lithium ion and organic electrolyte. A solvent of the organic electrolyte is composed of a mixed solvent mixed with a material having a propylene carbonate structure that at least one or more hydrogen atoms are substituted with a fluorine atom or a dimethyl carbonate or the like. Charge and discharge efficiency in the initial stage of a cycle of the negative electrode is improved, and a battery whose energy density is improved can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery comprising, as a negative electrode active material, one or more selected from the group consisting of carbon materials capable of electrochemically absorbing and releasing lithium ions. It is related to the improvement, especially compared with this type of lithium secondary battery using a conventional electrolyte by improving the organic electrolyte solvent, improving the charge and discharge efficiency of the negative electrode carbon material at the beginning of the cycle, and increasing the energy consumption. An energy density of a lithium secondary battery having a density is provided.

[0002]

2. Description of the Related Art In recent years, rapid progress in the electronics field has led to higher performance, smaller size, and more portable electronic devices, which has led to the demand for rechargeable high energy density secondary batteries used in these electronic devices. I'm getting stronger.

Conventional secondary batteries mounted on these electronic devices include lead storage batteries, nickel-cadmium storage batteries and nickel-hydrogen storage batteries. These batteries have low discharge voltage and high energy density. In terms of getting Recently, research and development of lithium secondary batteries using metallic lithium, lithium alloys, or carbon materials capable of electrochemically absorbing and desorbing lithium ions as the negative electrode active material and combining them with various positive electrodes have been carried out. Has been done. This type of battery is the most promising battery in the future as a secondary battery having a high battery voltage and a higher energy density per weight or volume than the conventional battery.

Initially, this type of secondary battery was studied in a system using metallic lithium or a lithium alloy for the negative electrode, but a negative electrode using metallic lithium or a lithium alloy is
There are problems in charge and discharge efficiency, pulverization, dendrite formation, etc., and at present, except for some, it has not been put to practical use. However, recently, it has been proposed to use a carbon material capable of electrochemically absorbing and desorbing lithium ions for the negative electrode. The negative electrode using this type of material has a higher average charge / discharge efficiency over the entire cycle as compared with the negative electrode using metallic lithium or a lithium alloy, and thus a lithium secondary battery having excellent charge / discharge reversibility can be constructed. . Further, in a battery using this kind of material as a negative electrode active material, a highly safe lithium secondary battery can be constructed without metal lithium being deposited in the battery, and it is now composed of a lithium-containing composite oxide. It was commercialized in combination with the positive electrode.

As an electrolyte used in a lithium secondary battery using a carbon material capable of electrochemically absorbing and desorbing lithium ions as the negative electrode active material, a cyclic ester having a high dielectric constant such as propylene carbonate is currently used. A non-aqueous mixed solvent containing a mixed solvent of a system solvent and a low-viscosity solvent such as diethyl carbonate as a main component and a lithium salt such as LiPF ₆ dissolved therein is used.

[0006]

A lithium secondary battery using a carbon material capable of electrochemically absorbing and desorbing lithium ions as a negative electrode active material is a lithium secondary battery using metallic lithium or a lithium alloy as the negative electrode active material. The cycle life is significantly longer than that of the battery, and the risk of short circuit due to the generation of lithium dendrite is extremely low, and therefore it is expected to be a high-performance secondary battery. However,
The charging / discharging efficiency of the negative electrode carbon material used here is 95% or more when viewed on average over the entire cycle, which is a high value as compared with the case where metallic lithium or a lithium alloy is used, but such a high value at the beginning of the cycle. Has not been obtained. And the low charge and discharge efficiency of the negative electrode not only causes the capacity to decrease due to the progress of the cycle of this type of lithium secondary battery, but when the negative electrode capacity is significantly lower than the positive electrode capacity, metallic lithium is deposited on the surface of the negative electrode active material during charging. Electrodeposition will occur, and the safety of this type of lithium secondary battery will be significantly reduced. As described above, in order to suppress deterioration of cycle life and safety, a method of previously adding a capacity loss amount of the carbon material at the beginning of the cycle at the time of manufacturing a battery is adopted. However, this approach comes at the expense of battery energy density.
This tendency is more remarkable as the crystallinity of the carbon material is higher.

As an improvement in the electrolytic solution for the purpose of improving the charge / discharge efficiency of the negative electrode carbon material, it has been studied to use ethylene carbonate instead of propylene carbonate as the high dielectric constant solvent. Since ethylene carbonate has a high freezing point of 36.4 ° C. and is a solid at room temperature, it is difficult to handle, and it is considered that this method has no high industrial value.

The present invention relates to a lithium secondary battery using a carbon material capable of electrochemically absorbing and desorbing lithium ions as a negative electrode active material, as compared with a battery of this type using a conventional electrolytic solution. Provide an organic electrolyte solvent that improves the charge and discharge efficiency of the negative electrode in the initial stage, is easy to handle, and provides a lithium secondary battery having a larger energy density than this type of battery using a conventional electrolyte. It is a thing.

[0009]

Means for Solving the Problems In the present invention, as a means for solving the above problems, one or more active materials selected from the group consisting of carbon materials capable of electrochemically absorbing and desorbing lithium ions are used. A lithium secondary battery comprising an organic electrolyte, and a negative electrode having the following formula, a positive electrode having as active material one or more selected from the group consisting of substances capable of electrochemically absorbing and releasing lithium ions, The above-mentioned organic electrolytic solution is characterized in that it has, as a solvent, one or two or more kinds of propylene carbonate in which at least one or more hydrogens out of six hydrogens are replaced with fluorine.

At least one of the six hydrogens referred to here
Propylene carbonate in which at least one hydrogen has been replaced by fluorine (hereinafter referred to as fluorine-substituted propylene carbonate)
Is an organic compound represented by the structural formula shown in Chemical formula 1,
For example, 3-fluoro-propylene carbonate, 4-fluoro-propylene carbonate, 3-difluoro-propylene carbonate, 3-fluoro-4-fluoropropylene carbonate, 3-difluoro-4-fluoro-propylene carbonate, 4-trifluoromethyl- Ethylene carbonate, 4-trifluoromethyl-3-fluoro-ethylene carbonate, 4-trifluoromethyl-4-fluoro-
Examples thereof include ethylene carbonate, 4-trifluoromethyl-3-difluoro-ethylene carbonate, 4-trifluoromethyl-3-fluoro-4-fluoro-ethylene carbonate, and perfluoro-propylene carbonate.

[0011]

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Even if the fluorine-substituted propylene carbonate is used alone, it is effective in suppressing the reaction between the negative electrode carbon material of the lithium secondary battery and the electrolytic solution, but the fluorine-substituted propylene carbonate is used as the first solvent and the second solvent. It may be used as a mixture with other solvent, and is not particularly limited, but for example, tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3- Cyclic ethers such as dioxolane and 1,4-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol Chain ethers such as polyol-dialkyl ether, tetraethylene glycol dialkyl ether, etc., dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, butyl propyl When mixed with a solvent having a lower viscosity than fluorine-substituted propylene carbonate, such as carbonates, dibutyl carbonate, alkyl propionate, dialkyl malonate, alkyl esters of acetic acid, etc., the viscosity of the mixed solvent as a whole decreases. Thus, an electrolytic solution solvent excellent in high rate charge / discharge property can be obtained. In particular, when one or more selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate and one or more fluorine-substituted propylene carbonate are mixed, It is possible to obtain a solvent for organic electrolyte having low reactivity with a negative electrode carbon material and excellent in high rate charge / discharge characteristics.

Further, the fluorine-substituted propylene carbonate can be used as a mixture with another solvent having a high dielectric constant,
The other solvent having a high dielectric constant is not particularly limited, and examples thereof include propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2 methyl-γ-butyrolactone and acetyl-γ-butyrolactone. , Γ-valerolactone and the like. In particular, carbonic acid esters are electrochemically stable, and those having short side chains have particularly high electrochemical stability and low viscosity, and those having unsaturated bonds are electrochemically stable. It is preferable to use ethylene carbonate, propylene carbonate alone or mixed with a mixture of ethylene carbonate and propylene carbonate because of their high properties.

When the fluorine-substituted propylene carbonate is mixed with another solvent to be used as the electrolytic solution solvent, the mixing ratio thereof is not particularly limited, but compared with the conventional electrolytic solution solvent such as propylene carbonate. Although it is effective in suppressing the reaction between the negative electrode carbon material of the lithium secondary battery and the electrolytic solution, in particular, the volume of the first solvent containing one or more fluorine-substituted propylene carbonates is the above-mentioned organic electrolytic solution solvent. Of the second solvent is 30% or more in the total volume, and is selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate. The volume of
The ratio of the total volume of the organic electrolyte solution solvent is 40% or more, and the volume of the mixed solvent of the first group solvent and the second solvent is 8% of the total volume of the organic electrolyte solution solvent.
When it is 0% or more, particularly good charge and discharge characteristics are obtained.

The lithium salt used here is not particularly limited as long as it dissociates in an organic solvent and supplies lithium ions.
iClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ ,
Inorganic lithium salts such as LiCl and LiBr, and LiB
_{(C 6 H 5) 4,} LiN (SO 2 CF 3) 2, LiC
_{(SO 2 CF 3) 3,} LiOSO 2 CF 3, LiOSO
₂ C ₂ F ₅ , LiOSO ₂ C ₃ F ₇ , LiOSO ₂ C ₄
F ₉ , LiOSO ₂ C ₅ F ₁₁ , LiOSO ₂ C ₆ F
₁₃ , there are organic lithium salts such as LiOSO ₂ C ₇ F _15, but lithium salts containing fluorine are preferable from the viewpoint of safety, and LiPF ₆ is particularly preferable because it has high conductivity.
It is preferable to use iPF ₆ alone or a mixed lithium salt containing other lithium salt containing LiPF ₆ as a main component.

The positive electrode active material may be LiCoO 2.
₂ , lithium-containing composite oxides such as LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , TiO ₂ , MnO ₂ , MoO
_{3, V 2 O 5, TiS} 2, MoS chalcogen compounds such as _2, such as, but are not particularly limited as long as the lithium ion can electrochemically occlude and release, discharge voltage is high, high cycle stability Since it has a property, Li
Α-NaC such as CoO ₂ , LiNiO ₂ and LiMnO ₂
A lithium compound having a rO ₂ structure or LiMn
_It is preferable to use ₂ O ₄ .

[0017]

The present inventors have found that most of the charge / discharge efficiency at the beginning of the cycle of a lithium secondary battery using a carbon material as the negative electrode active material is low in the electrolyte solvent and the negative electrode carbon material. It is believed to be due to an irreversible reaction with chemically active sites. In fact, this type of battery using propylene carbonate as the electrolyte solvent of a lithium secondary battery, which uses a carbon material capable of electrochemically absorbing and desorbing lithium ions as the negative electrode active material, is charged and discharged for about 10 cycles. After disassembling, the surface of the negative electrode was observed, and it was observed that a polymer-like product apparently regarded as a reaction product of propylene carbonate and the negative electrode carbon material covered the surface of the negative electrode. Such a reaction product is not found in a system using metallic lithium or a lithium alloy as the negative electrode active material, but is considered to be specifically found when a carbon material is used.

In the lithium secondary battery using a carbon material as the negative electrode active material, the inventors of the present invention can reduce the chemical reactivity of the organic electrolytic solution by halogenating the solvent of the organic electrolytic solution. As a result, it was thought that the reaction between the negative electrode carbon material and the electrolytic solution solvent could be greatly suppressed.

Among the halogen-based organic solvents, the fluorine-based one is selected because (1) the CF bond is different from other halogen-based organic solvents.
It is overwhelmingly strong and less likely to decompose. (2) The atomic radius of fluorine is almost the same as that of hydrogen, and the structure and size closest to the original non-halogenated organic solvent are used compared to other halogens. This is because the toxicity of the (3) fluorine-based organic solvent to the human body is extremely lower than that of other halogen-based organic solvents and the human safety is high.

The cyclic carbonic acid ester structure was selected among the fluorine-based organic solvents because the cyclic carbonic acid ester typified by ethylene carbonate and propylene carbonate itself is a solvent of the organic electrolytic solution for lithium secondary batteries. Was used as a negative electrode carbon material due to the high dielectric constant originally possessed by the non-fluorinated cyclic ester carbonate and the fluorination by using the fluorinated one. This is because an organic solvent sharing the reaction suppressing action with

Further, among the fluorine-based organic solvents having a cyclic carbonic acid ester structure, one having a propylene carbonate structure is selected because, in general, fluorination of an organic solvent is accompanied by an increase in freezing point. If so, the freezing point becomes too high, and if the side chain extends beyond the butylene carbonate structure, the viscosity increases sharply and the chemical and electrochemical stability decreases, and it has an unsaturated bond like vinylene carbonate. This is because those having lower electrochemical stability than those having no unsaturated bond are practically disadvantageous.

Even if such a fluorine-substituted propylene carbonate is used alone as a solvent for an organic electrolytic solution for a lithium secondary battery, it has a great effect on suppressing the reaction between the negative electrode carbon material and the electrolytic solution. There are several types of substances, which have similar properties to each other, and there is no problem if two or more types of fluorine-substituted propylene carbonates are mixed and used.

Although the fluorine-substituted propylene carbonate having such characteristics has a slight decrease in viscosity as compared with propylene carbonate due to the introduction of fluorine into the molecule, it has a high viscosity as a solvent used in a lithium secondary battery. Which is a solvent belonging to the category of fluorinated propylene carbonate, as in the case of using propylene carbonate, it is better to use a fluorine-substituted propylene carbonate mixed with a solvent having a lower viscosity than the fluorinated propylene carbonate alone. The mobility of lithium ions in the interior is increased, the conductivity is improved, and the polarization during charging / discharging can be reduced. Thus, when used in a lithium secondary battery, it reacts with the negative electrode carbon material. It is possible to obtain a lithium secondary battery that has a suppressing effect and is also excellent in high rate charge / discharge characteristics.

Further, as a result of the present inventors' study of combining fluorine-substituted propylene carbonate with various low-viscosity solvents, it was found that in a lithium secondary battery using a carbon material as a negative electrode active material, the organic electrolyte was When having a mixed solvent of one or more selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate and one or more selected from fluorine-substituted propylene carbonate. It has been found that a characteristic in which the reaction suppressing action with the negative electrode carbon material and the high rate charge / discharge characteristic are compatible at a particularly high level can be obtained. Dimethyl carbonate,
A lithium secondary battery of this kind provided with an organic electrolyte having a mixed solvent of a fluorine-substituted propylene carbonate and a solvent selected from the group consisting of methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate is Compared with a lithium secondary battery of this type provided with an organic electrolyte having a mixed solvent of a low-viscosity solvent and a fluorine-substituted propylene carbonate, particularly good charge and discharge characteristics can be obtained from dimethyl carbonate, methyl ethyl carbonate, diethyl ether. This is because the solvent selected from the group consisting of carbonate, methylpropyl carbonate and methylbutyl carbonate is more stable and less likely to be decomposed with respect to radicals generated in the battery, as compared with other low viscosity solvents. Further, the solvent selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, and methyl butyl carbonate can obtain the viscosity reducing effect even if it is mixed with fluorine-substituted propylene carbonate alone. Since the chain carbonates are solvents having similar characteristics to each other, there is no problem even if two or more kinds of them are mixed and used.

As described above, when the fluorine-substituted propylene carbonate and a solvent other than the fluorine-substituted propylene carbonate are mixed and used in an electrolyte solution for a lithium secondary battery using a carbon material as the negative electrode active material, the mixing ratio should be specified. Even if compared with using a conventional electrolytic solution, the reaction between the electrolytic solution and the negative electrode carbon material is suppressed, and if the solvent mixed with the fluorine-substituted propylene carbonate is a low-viscosity solvent, the effect of reducing the viscosity by the addition is Although confirmed, the present inventors set the mixing ratio to a level in mixing with various solvents and examined the charge / discharge characteristics of this type of lithium secondary battery using each organic electrolyte. As a result, the mixing conditions of the mixed solvent are such that the volume of the first group solvent composed of one or more of fluorine-substituted propylene carbonate occupies the whole volume of the organic electrolyte solution solvent. The solvent selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate is 0% or more, and the volume of the second group solvent consisting of 1 or 2 or more is the above-mentioned. The proportion of the total volume of the organic electrolyte solution solvent is 40% or more, and the volume of the mixed solvent of the first group solvent and the second group solvent occupies the total volume of the organic electrolyte solution solvent. Is 80%
When the above conditions are satisfied, it has a particularly large effect in suppressing the reaction between the negative electrode carbon material and the organic electrolytic solution, as compared with this type of lithium secondary battery using a conventional electrolytic solution,
As a result, it was found that a lithium secondary battery having a particularly large energy density and particularly excellent high rate charge / discharge characteristics can be obtained as compared with this type of lithium secondary battery using a conventional electrolytic solution. .

It is necessary that the volume of the first group solvent occupy 30% or more of the total volume of the organic electrolyte solution solvent, that is, the volume of the first group solvent occupies the total volume of the organic electrolyte solution solvent. This is because when the ratio is 30% or more, a particularly large effect can be seen in suppressing the reaction between the negative electrode carbon material and the organic electrolytic solution, and the ratio of the second group solvent to the total volume of the organic electrolytic solution solvent is 40%. It is necessary to be above. When the volume of the second group solvent is 40% or more of the total volume of the organic electrolyte solution solvent, particularly high conductivity is obtained, and particularly good high rate charge / discharge characteristics are obtained. This is because it is obtained, and the volume of the mixed solvent of the first group solvent and the second group solvent needs to be 80% or more of the total volume of the organic electrolytic solution solvent. The volume accounts for 20% of the total volume of the organic electrolyte solvent. By weight, is due to the presence of other solvents is not affected so large.

Examples of the present invention will be described below.

[0028]

[Example 1] As a test negative electrode, a coke fired body powder, a styrene-butadiene rubber-based resin, and ethyl acetate were mixed by stirring with a homogenizer to obtain a slurry-like active material mixture, which was then composed of a copper foil. The active material mixture described above to the current collector, using a slot die coater, after coating on one surface, dried in an oven to remove the solvent, to form an active material mixture coating film on the current collector, then Then, each current collector having the coating film was subjected to a heat treatment to cure the styrene-butadiene rubber resin in the coating film. Then, the active material coating film surface of each current collector having the active material mixture coating film was compressed by a heating roller press machine to homogenize the active material coating film to obtain a test negative electrode. The obtained electrode plate was subjected to heat treatment to remove water.

Metallic lithium was used for the counter electrode and the reference electrode and combined with the test negative electrode to form a three-electrode beaker type cell.

The organic electrolytes shown in Table 1, Examples A to C, and Conventional Example A were injected into the cells thus prepared.

[0031]

[Table 1]

In Table 1, 3-fluoro-4-fluoro-propylene carbonate, which is a fluorine-substituted propylene carbonate, is 3-F-4-F-PC, 3-fluoro-propylene carbonate is 3-F-PC, and 4 -Fluoro-propylene carbonate is abbreviated as 4-F-PC.
Further, in Table 1, propylene carbonate is abbreviated as PC.

Using these cells, at a temperature of 25 ° C,
The test negative electrode was charged at a current density of 0.1 mA / cm ² until the potential of the test negative electrode became OV with respect to the reference electrode (sodium ions were absorbed), and after 10 minutes of rest, the test negative electrode was charged at the same current density. The battery was discharged until the potential became 1.5 V with respect to the reference electrode (lithium ions were released).

Table 2 shows Examples A to C and Conventional Example A.
2 shows the charging / discharging efficiency of the cell using.

[0035]

[Table 2]

From this, it can be seen that the charge / discharge efficiency of the test negative electrode coke fired bodies when using the electrolytes of Examples A to C according to the present invention is higher than that when using Conventional Example A.

Further, when the test negative electrode after charging and discharging was examined, a polymer substance was observed on the surface in the case of using the conventional example A, whereas it was clearly observed in the examples A to C. There wasn't.

[0038]

Example 2 The same triode type beaker cell as in Example 1 was used except that artificial coke powder was used as the active material of the test negative electrode instead of the coke calcined body powder, and this was described in Table 1 above. The organic electrolyte, Example A to Example C, Conventional Example A and Conventional Example B were injected, and the potential of the test negative electrode was OV with respect to the reference electrode at a temperature of 25 ° C. and a current density of 0.1 mA / cm ^2. The battery was charged until it became (a lithium ion was absorbed), and after 10 minutes of rest, it was discharged at the same current density until the potential of the test negative electrode became 1.5 V with respect to the reference electrode (the lithium ion was released). ).

Table 3 shows Examples A to C and Conventional Example A.
2 shows the charging / discharging efficiency of the cell using.

[0040]

[Table 3]

In the cell using the electrolytic solution of Conventional Example A, almost all the charging current was consumed by the reaction between the electrolytic solution and the test negative electrode carbon material, and the capacity could not be taken out by discharging. According to the present invention, cells using the electrolytic solution of Examples A to C can be charged and discharged, and even in artificial graphite having high reactivity with an electrolytic solution solvent, fluorine-substituted propylene in an organic electrolytic solution is used. It can be seen that the use of carbonate has a great effect on suppressing the reaction between the electrolytic solution solvent and the carbon material.

Further, when a test negative electrode after charging and discharging was examined, a polymer substance was observed on the surface in the case of the conventional example A, but clearly in the examples A to C. Not observed.

[0043]

Example 3 The same triode beaker cell as in Example 1 was used, and the organic electrolytes shown in Table 4, Example D to Example L, Conventional Example B and Conventional Example C were injected. After charging at a temperature of 25 ° C. and a current density of 1.0 mA / cm ² until the potential of the test negative electrode reaches OV with respect to the reference electrode (soaking lithium ions), the same after 10 minutes rest. It was discharged at a current density until the potential of the test negative electrode became 1.5 V with respect to the reference electrode (released lithium ions).

[0044]

[Table 4]

In Table 4, 3-fluoro-4-fluoro-propylene carbonate is abbreviated as 3-F-4-F-PC.

In Table 4, propylene carbonate was added to P
C, dimethyl carbonate to DMC, methyl ethyl carbonate to MEC and diethyl carbonate to DEC
MPC for methyl propyl carbonate, MBC for methyl butyl carbonate, DM for dimethoxyethane
E, tetrahydrofuran is abbreviated as THF, ethyl butyl carbonate is abbreviated as EBC, and dibutyl carbonate is abbreviated as DBC.

Table 5 shows Examples D to L and Conventional Example B.
2 shows the charge and discharge efficiency of the cell using Conventional Example C.

[0048]

[Table 5]

It was confirmed that the charge and discharge efficiencies of the test negative electrodes when using the electrolytic solutions of Examples D to L according to the present invention were much higher than those when using Conventional Example B and Conventional Example C. As a result, the fluorine-substituted propylene carbonate is effective in suppressing the reaction between the test negative electrode and the electrolytic solution even when it is mixed with various low-viscosity solvents, and has a large charge / discharge efficiency as compared with the conventional electrolytic solution. It turns out that is obtained.

Further, by comparing the group of Examples D to H with the group of Examples I to L, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, When using a solvent selected from the group consisting of methylbutyl carbonate, the charge and discharge efficiency of the test negative electrode shows a high value far exceeding 80%, and has a lower viscosity than other ethers or chain carbonates having a large molecular weight. It can be seen that particularly high charge / discharge efficiency is obtained when a solvent selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate is used as the solvent.

Further, as compared with Example 1, high charge / discharge characteristics were obtained even when charge / discharge was performed at a current density 10 times higher. Therefore, coke was prepared by mixing the fluorine-substituted propylene carbonate with a low-viscosity solvent. It can be seen that an organic electrolyte solution having a high charging / discharging efficiency of a carbon material composed of a fired body and excellent in high rate charging / discharging property can be obtained.

[0052]

Example 4 The same three-electrode type beaker cell as in Example 2 was used, in which the organic electrolytic solution described in Table 4 above and Example D were used.
Example L, Conventional Example B, and Conventional Example C are injected at 25 ° C.
At a temperature of 1.0 mA / cm ^{2 at} a current density of 1.0 mA / cm ² until the potential of the test negative electrode reaches OV with respect to the reference electrode (soak up lithium ions), and after a 10-minute rest, at the same current density. , Was discharged until the potential of the test electrode became 1.5 V with respect to the reference electrode (released lithium ions).

Table 6 shows Examples D to L and Conventional Example B.
2 shows the charge and discharge efficiency of the cell using Conventional Example C.

[0054]

[Table 6]

In the cells using the electrolytic solutions of the conventional examples B and C, almost all the charging current was consumed by the reaction between the electrolytic solution and the carbon material as the test negative electrode, and the capacity could be taken out by discharging. On the other hand, the cells using the electrolytic solutions of Examples D to L according to the present invention can be charged and discharged, and as a result, the fluorine-substituted propylene carbonate is used by mixing with various low-viscosity solvents. However, as in the case of using the coke calcined body for the test negative electrode, even in the system using artificial graphite having high reactivity with the electrolytic solution for the test negative electrode, it is great in suppressing the reaction between the electrolytic solution and the carbon material. It turns out that it is effective.

Also, a group of Examples D to H and Example I.
In comparison with the group of Example L to Example L, Examples D to H using a solvent selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate as a low viscosity solvent. The charge and discharge efficiency of the test electrode when using the electrolytic solution shows a high value, than using other ethers and chain carbonate having a large molecular weight, as a low viscosity solvent, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, It can be seen that particularly high charge / discharge efficiency can be obtained when a solvent selected from the group consisting of methylpropyl carbonate and methylbutyl carbonate is used.

Further, similar to Example 3 using the coke calcined body as the test negative electrode active material, compared with Example 2, high charge / discharge characteristics were obtained even when charging / discharging was performed at 10 times the current density. It is understood that by mixing the fluorine-substituted propylene carbonate with a low-viscosity solvent, an organic electrolyte having a high charge / discharge efficiency and a high rate charge / discharge property of the carbon material made of artificial graphite can be obtained.

[0058]

Example 5 The same three-electrode beaker cell as in Example 1 was used, and the organic electrolytes shown in Table 7 below, Examples M to T, were injected into the cells at 25 ° C. , 1.0 mA
At a current density of / cm ² , the potential of the test electrode is O with respect to the reference electrode.
Charge to V (allow lithium ions to occlude), 1
After a 0-minute rest, the test electrode was discharged at the same current density until the potential of the test electrode became 1.5 V with respect to the reference electrode (lithium ions were released).

In Table 7, 3-fluoro-4-fluoro-propylene carbonate which is a fluorine-substituted propylene carbonate is abbreviated as 3-F-4-F-PC. Also, Table 7
Among them, diethyl carbonate is abbreviated as DEC.

[0060]

[Table 7]

Table 8 shows the discharge capacities and charge / discharge efficiencies of the cells using Examples M to T. However,
In Table 8 below, the discharge capacity ratio is a numerical value represented by Formula 1.

[0062]

(Equation 1)

[0063]

[Table 8]

The charging / discharging characteristics were evaluated by changing the mixing ratio of 3-fluoro-4-fluoro-propylene carbonate which is the fluorine-substituted propylene carbonate which is the first solvent and diethyl carbonate which is the second group solvent. As the ratio of -4-fluoro-propylene carbonate increases, the charging / discharging efficiency tends to increase.
-When fluoro-4-fluoro-propylene carbonate had a volume ratio of 30% or more based on all solvents, a high charge / discharge efficiency of 80% or more was obtained. The discharge capacity is 3-fluoro-4-.
As the ratio of fluoro-propylene carbonate increased, it first showed an increasing tendency, and thereafter, 3-fluoro-4-fluoro-propylene carbonate showed a maximum value in the vicinity of 50% by volume with respect to all the solvents, and thereafter. , Shows a decreasing trend. From this, the volume of the fluorine-substituted propylene carbonate that is the first group solvent accounts for 30% or more of the total volume of the organic electrolyte solution, and the volume of the second group solvent is the total volume of the organic electrolyte solution solvent. It can be seen that when the ratio of the battery to the test electrode coke is 40% or more, the reactivity between the test electrode coke calcined product and the electrolytic solution is particularly low, and the high-rate charge / discharge property is also particularly excellent.

[0065]

Example 6 The same triode type beaker cell as in Example 2 was used, in which the organic electrolytic solution described in Table 7 above, Example M were used.
Example T was injected from and at a temperature of 25 ° C., 1.0 mA /
At a current density of cm ² , the test electrode potential is OV with respect to the reference electrode.
Charge until it becomes (occlude lithium ion), 10
After resting for a minute, the test electrode was discharged at the same current density until the potential of the test electrode became 1.5 V with respect to the reference electrode (lithium ions were released).

Table 9 shows the discharge capacities and charge / discharge efficiencies of the cells using Examples M to T. However,
In Table 9, the discharge capacity ratio is the numerical value shown by the equation 1.

[0067]

[Table 9]

The first solvent, 3-fluoro-4-fluoro-
When the charge / discharge characteristics were evaluated by changing the mixing ratio of propylene carbonate and diethyl carbonate as the second solvent, the charge / discharge efficiency increased as the ratio of 3-fluoro-4-fluoro-propylene carbonate increased. When a tendency was observed and the volume ratio of 3-fluoro-4-fluoro-propylene carbonate to the total solvent was 30% or more, 75
A high charge / discharge efficiency of over% was obtained. In addition, the discharge capacity first showed an increasing tendency as the ratio of 3-fluoro-4-fluoro-propylene carbonate increased, and thereafter, the volume ratio of 3-fluoro-4-fluoro-propylene carbonate was 50% in all the solvents. The maximum value was shown in the vicinity, and then it showed a decreasing tendency. From this, the volume of the fluorine-substituted propylene carbonate that is the first solvent is 30% or more of the total volume of the organic electrolyte solution, and the volume of the second group solvent is the total volume of the organic electrolyte solution. It can be seen that when the ratio of the charge to the test electrode is 40% or more, the reactivity between the test electrode artificial graphite and the electrolytic solution is particularly low, and the charge / discharge characteristics are also excellent especially in the high rate charge / discharge property.

[0069]

Example 7 A triode beaker cell similar to that of Example 1 was used, and the organic electrolytes described in Table 10 below, Examples U to Z, and Examples A to A were used. D is injected and charged at a temperature of 25 ° C. and a current density of 1.0 mA / cm ² until the potential of the test electrode becomes OV with respect to the reference electrode (soak up lithium ions) and pause for 10 minutes. After,
At the same current density, the potential of the test electrode is 1.5 with respect to the reference electrode
Discharged to V (released lithium ions).

[0070]

[Table 10]

In Table 10, 3-fluoro-4-fluoro-propylene carbonate, which is a fluorine-substituted propylene carbonate, is abbreviated as 3-F-4-F-PC. In Table 10, diethyl carbonate is abbreviated as DEC and ethyl butyl carbonate is abbreviated as EBC.

Table 11 shows Example U to Example Z, and
6 shows the charge / discharge efficiency of cells using Conventional Example A and Conventional Example A.

[0073]

[Table 11]

The first solvent, 3-fluoro-4-fluoro-
When a solvent other than the first solvent and the second solvent was added to a mixed solvent of propylene carbonate and diethyl carbonate which is the second solvent, as shown here, the volume of the mixed solvent of the first solvent and the second solvent was When using an electrolytic solution in which the proportion of the total volume of the organic electrolytic solution total solvent is 80% or more, the test electrode coke is not significantly affected by the newly added solvent other than the first solvent and the second solvent. It can be seen that a high charge / discharge efficiency of 80% or more can be obtained for the fired body.

[0075]

Example 8 The same three-electrode type beaker cell as in Example 2 was used, in which the organic electrolytic solution shown in Table 10, Example U to Example Z, and Example A to Example D, Inject
Charge at a temperature of 25 ° C. and a current density of 1.0 mA / cm ² until the potential of the test electrode becomes OV with respect to the reference electrode (soak up lithium ions), and then rest for 10 minutes at the same current. At the density, the test electrode was discharged until the potential of the test electrode was 1.5 V with respect to the reference electrode (lithium ions were released).

Table 12 shows Examples U to Z, and
6 shows the charge / discharge efficiency of cells using Conventional Example A and Conventional Example A.

[0077]

[Table 12]

The first solvent, 3-fluoro-4-fluoro-
When a solvent other than the first solvent and the second solvent was added to a mixed solvent of propylene carbonate and diethyl carbonate which is the second solvent, as shown here, the volume of the mixed solvent of the first solvent and the second solvent was When an electrolytic solution in which the proportion of the total volume of the organic electrolytic solution total solvent is 80% or more is used, the test electrode is not significantly affected by the newly added solvent other than the first solvent and the second solvent. It can be seen that the charge / discharge efficiency as high as 75% or more can be obtained even if artificial graphite having high reactivity with the electrolyte solvent is used.

[0079]

[Embodiment 9] A negative electrode and a positive electrode are opposed to each other via a separator, and the electrolytic solutions of Example D, Example F, Conventional Example B, and Conventional Example C shown in Table 13 are injected to prepare coin type batteries. Fifty electrolyte solutions were prepared.

[0080]

[Table 13]

All of the coin type batteries were designed so that the capacity ratio of the positive and negative electrodes during battery preparation was 1: 1 and only the composition of the electrolytic solution was taken as a standard. 30 pieces were prepared for each electrolytic solution.

The negative electrode was prepared by mixing the powder of the coke fired product, the styrene-butadiene rubber-based resin and ethyl acetate with stirring with a homogenizer to obtain a negative electrode active material mixture in the form of a slurry, and then comprising a copper foil. The above-mentioned negative electrode active material mixture to the current collector, using a slot die coater, after coating on one side, dried in an oven to remove the solvent, to form an active material mixture coating film on the current collector, Subsequently, each current collector having the coating film is subjected to heat treatment to cure the styrene-butadiene rubber-based resin in the coating film, and thereafter, the activity of each current collector having the active material mixture coating film is activated. It was obtained by subjecting the surface of the material coating film to compression treatment with a heating roller press to homogenize the active material coating film. The obtained electrode plate was subjected to heat treatment to remove water.

On the other hand, for the positive electrode, LiCoO ₂ powder, graphite powder as a conductive material, polyvinylidene fluoride resin as a binder, and N-methylpyrrolidone were mixed by stirring with a homogenizer to prepare a slurry positive electrode active material. A mixture is obtained, and then the positive electrode active material mixture is applied to one side of a current collector made of aluminum foil, dried in an oven at 100 ° C., the solvent is removed, and the activity on the current collector is obtained. It is obtained by forming a material mixture coating film, and further rolling the active material coating film surface of the current collector having the active material mixture coating film with a roller press machine to homogenize the active material coating film. It was The obtained electrode plate was heat-treated in a vacuum oven to remove water.

As the separator, a microporous film of polyolefin (polypropylene, polyethylene or a copolymer thereof) having a three-dimensional pore structure (sponge shape) wider than the positive and negative electrode plates was used.

The battery thus prepared was charged at a maximum charge current of 0.2 C at a temperature of 25 ° C. using a charge / discharge measuring device.
At a current value of mA, the battery voltage is 4.1 from the charging direction.
The battery was charged until it reached V, and after 10 minutes of rest, it was discharged at the same current until it reached 2.75 V, and the discharge capacities of the first cycle of each battery were compared.

The discharge capacity in the first cycle is 1 of that of Conventional Example B.
The discharge capacity at the second cycle was set as 100 and shown as a percentage for comparison.

Table 14 shows the discharge capacity ratio at the first cycle of the battery using each electrolyte. The values in Table 14 are the average of 30 cells in each electrolytic solution.

[0088]

[Table 14]

As described above, it can be seen that the discharge capacity of the battery using the electrolytic solution of the example is increased as compared with the battery using the electrolytic solution of the conventional example. The discharge capacity in the first cycle was improved because the battery using the electrolytic solution of the Example had a lower reactivity between the negative electrode coke fired body and the electrolytic solution and a higher charge / discharge rate than the battery using the electrolytic solution of the conventional example. This is because it has efficiency.

Therefore, from the present experiment, the present invention shows that in the lithium secondary battery using the carbon material of the coke calcined body as the negative electrode active material, it is larger than this type of battery using the conventional electrolyte. It can be seen that the lithium secondary battery having an energy density and excellent cycle characteristics is supplied.

[0091]

[Example 10] A negative electrode and a positive electrode were opposed to each other via a separator, and the electrolytic solutions of Example D, Example F, and Conventional Example B to Conventional Example D described in Table 15 were injected to form a coin-type battery. 30 pieces were produced for each electrolytic solution.

[0092]

[Table 15]

All of the coin-type batteries were designed so that the capacity ratio of the positive and negative electrodes during battery preparation was 1: 1 and only the composition of the electrolytic solution was taken as a standard. 30 pieces were prepared for each electrolytic solution.

The negative electrode was produced in the same manner as in Example 9 except that artificial graphite powder was used instead of coke burned powder as the active material. On the other hand, the positive electrode was manufactured by the same manufacturing method as in Example 9. The same separator as in Example 9 was used.

The thus-prepared battery was charged at a temperature of 25 ° C. with a charge / discharge measuring device to obtain a maximum charge current of 0.2 C.
At a current value of mA, the battery voltage is 4.1 from the charging direction.
The battery was charged until it reached V, and after 10 minutes of rest, it was discharged at the same current until it reached 2.75 V, and the discharge capacities of the first cycle of each battery were compared.

Table 16 shows the discharge capacity ratio at the first cycle of the battery using each electrolytic solution.

[0097]

[Table 16]

As described above, in the batteries having the electrolytic solution using propylene carbonate as the high dielectric constant component shown in Conventional Example B and Conventional Example C, almost all of the charge capacity of the positive electrode was due to the reaction between the negative electrode artificial graphite and the electrolytic solution. It was consumed and the capacity could not be taken out by discharge. Propylene carbonate cannot be used in a system in which a carbon material with high crystallinity such as artificial graphite is used as a negative electrode, and in the conventional technology, propylene carbonate has a high reactivity with a carbon material with high crystallinity such as artificial graphite. Since it is lower than carbonate, its melting point is 36.4 ° C higher,
Inevitably, there was no choice but to use ethylene carbonate, which had a handling problem because it was a solid at room temperature, but the battery of the present invention using fluorine-substituted propylene carbonate as the high dielectric constant component of the electrolytic solution can be sufficiently charged and discharged. Therefore, both the first cycle discharge capacity and the 500th cycle discharge capacity maintenance rate are
Charge / discharge characteristics were obtained that were even higher than those of the battery (Example C) having the electrolytic solution using ethylene carbonate as the high dielectric constant component. This is similar to the case where the coke calcined body is used as the negative electrode active material, in this type of battery using the electrolytic solution of the example, the reaction between the negative electrode artificial graphite and the electrolytic solution is greater than that in the battery using the electrolytic solution of the conventional example. This is because the property is low and the charge and discharge efficiency is high.
Further, since fluorine-substituted propylene carbonate is a liquid at room temperature, it is an excellent solvent in terms of handling as compared with ethylene carbonate. Therefore, from this experiment, the lithium secondary battery using the carbon material as the negative electrode active material using the electrolytic solution of the present invention uses artificial graphite as the active material, as in the case of using the coke calcined body as the negative electrode active material. Even in this case, it is understood that the lithium secondary battery having a large energy density and excellent cycle characteristics is supplied as compared with the battery of this type using the conventional electrolytic solution.

In Examples 1 and 2 described above, examples using 3-fluoro-4-fluoro-propylene carbonate, 3-fluoro-propylene carbonate and 4-fluoro-propylene carbonate as the fluorine-substituted propylene carbonate were described. Of 6 hydrogens, propylene carbonate in which at least one hydrogen is replaced by fluorine may be used, and 3-difluoro-propylene carbonate, 3-difluoro-4-fluoro-propylene carbonate, 4-trifluoromethyl-ethylene. Carbonate, 4
-Trifluoromethyl-3-fluoro-ethylene carbonate, 4-trifluoromethyl-4-fluoro-ethylene carbonate, 4-trifluoromethyl-3-difluoro-ethylene carbonate, 4-trifluoromethyl-3-fluoro-4- Similar effects could be confirmed even when other fluorine-substituted propylene carbonate such as fluoro-ethylene carbonate and perfluoro-propylene carbonate was used.

In the above-mentioned Examples 3 and 4, an example using 3-fluoro-4-fluoro-propylene carbonate as the fluorine-substituted propylene carbonate was described.
Propylene carbonate obtained by substituting at least one or more hydrogen with fluorine among the individual hydrogens may be used, and 3-fluoro-propylene carbonate, 4-fluoro-propylene carbonate, 3-difluoro-propylene carbonate, 3-difluoro-4. -Fluoro-propylene carbonate, 4-trifluoromethyl-ethylene carbonate, 4
-Trifluoromethyl-3-fluoro-ethylene carbonate, 4-trifluoromethyl-4-fluoro-ethylene carbonate, 4-trifluoromethyl-3-difluoro-ethylene carbonate, 4-trifluoromethyl-3-fluoro-4- Similar effects could be confirmed even when other fluorine-substituted propylene carbonate such as fluoro-ethylene carbonate and perfluoro-propylene carbonate was used.
As the low-viscosity solvent, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, dimethoxyethane, tetrahydrofuran, ethyl butyl carbonate and dibutyl carbonate were used.
It is not particularly limited, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran,
1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether,
Other low viscosity such as triethylene glycol-dialkyl ether, tetraethylene glycol dialkyl ether, ethyl propyl carbonate, dipropyl carbonate, butyl propyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester and other chain-like esters The same effect was confirmed even when a solvent was used. Further, as the low-viscosity solvent, the system in which only one kind is mixed with the fluorine-substituted propylene carbonate has been described, but the same effect can be confirmed by mixing two or more kinds of the low-viscosity solvent with the fluorine-substituted propylene carbonate. .

In the above-mentioned Examples 5 and 6, examples using 3-fluoro-4-fluoro-propylene carbonate as the fluorine-substituted propylene carbonate were described.
Propylene carbonate obtained by substituting at least one or more hydrogen with fluorine among the individual hydrogens may be used, and 3-fluoro-propylene carbonate, 4-fluoro-propylene carbonate, 3-difluoro-propylene carbonate, 3-difluoro-4. -Fluoro-propylene carbonate, 4-trifluoromethyl-ethylene carbonate, 4
-Trifluoromethyl-3-fluoro-ethylene carbonate, 4-trifluoromethyl-4-fluoro-ethylene carbonate, 4-trifluoromethyl-3-difluoro-ethylene carbonate, 4-trifluoromethyl-3-fluoro-4- Similar effects could be confirmed even when other fluorine-substituted propylene carbonate such as fluoro-ethylene carbonate and perfluoro-propylene carbonate was used.
Although diethyl carbonate was used as the second solvent, the same effect could be confirmed by using another second solvent composed of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and methyl butyl carbonate. Further, as the second solvent, the system in which only one kind is mixed with the fluorine-substituted propylene carbonate is described, but the same is true even if two or more kinds of the second group solvent are mixed with the fluorine-substituted propylene carbonate. The effect was confirmed.

In the above-mentioned Examples 7 and 8, an example in which 3-fluoro-4-fluoro-propylene carbonate was used as the fluorine-substituted propylene carbonate was described.
Propylene carbonate obtained by substituting at least one or more hydrogen with fluorine among the individual hydrogens may be used, and 3-fluoro-propylene carbonate, 4-fluoro-propylene carbonate, 3-difluoro-propylene carbonate, 3-difluoro-4. -Fluoro-propylene carbonate, 4-trifluoromethyl-ethylene carbonate, 4
-Trifluoromethyl-3-fluoro-ethylene carbonate, 4-trifluoromethyl-4-fluoro-ethylene carbonate, 4-trifluoromethyl-3-difluoro-ethylene carbonate, 4-trifluoromethyl-3-fluoro-4- Similar effects could be confirmed even when other fluorine-substituted propylene carbonate such as fluoro-ethylene carbonate and perfluoro-propylene carbonate was used.
Although diethyl carbonate was used as the second solvent, the same effect could be confirmed by using another second solvent composed of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and methyl butyl carbonate. Further, as the second solvent, the system in which only one kind is mixed with the fluorine-substituted propylene carbonate has been described, but the same effect can be confirmed by mixing two or more kinds of the second solvent with the fluorine-substituted propylene carbonate. In addition, although ethylene carbonate or ethyl butyl carbonate was described as a solvent other than the first solvent and the second solvent, propylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2 methyl-γ-butyrolactone, acetyl-γ-butyrolactone. , Other high dielectric constant solvents such as γ-valerolactone, and tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,
3-dioxolane, alkyl-1,3-dioxolane,
1,4-dioxolane, 1,2-dimethoxyethane,
1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, tetraethylene glycol dialkyl ether, ethyl propyl carbonate, dipropyl carbonate, butyl propyl carbonate, dibutyl carbonate, propionic acid If one or more other low-viscosity solvents such as alkyl ester, dialkyl malonate, alkyl acetate, etc. are mixed in a mixed solvent of the first solvent and the second solvent, these first solvents may also be used. , Second
A solvent, a mixed solvent of one or more kinds of solvents other than ethylene carbonate and ethyl butyl carbonate, and one or more kinds of ethylene carbonate and ethyl butyl carbonate are mixed in the first group solvent and the second group solvent. The same effect could be confirmed whether it was used or not.

In the above-mentioned Examples 9 and 10, examples using 3-fluoro-4-fluoro-propylene carbonate as the fluorine-substituted propylene carbonate were described.
Of the six hydrogens, propylene carbonate in which at least one hydrogen is replaced by fluorine may be used, and 3-fluoro-propylene carbonate, 4-fluoro-propylene carbonate, 3-difluoro-propylene carbonate, 3-difluoro- 4-fluoro-propylene carbonate, 4-trifluoromethyl-ethylene carbonate, 4
-Trifluoromethyl-3-fluoro-ethylene carbonate, 4-trifluoromethyl-4-fluoro-ethylene carbonate, 4-trifluoromethyl-3-difluoro-ethylene carbonate, 4-trifluoromethyl-3-fluoro-4- Similar effects could be confirmed even when other fluorine-substituted propylene carbonate such as fluoro-ethylene carbonate and perfluoro-propylene carbonate was used.
Although dimethyl carbonate or diethyl carbonate was used as the second solvent, the same effect could be confirmed by using another second solvent composed of methyl ethyl carbonate, methyl propyl carbonate and methyl butyl carbonate. Further, as the second solvent, the system in which only one kind is mixed with the first solvent has been described, but the same effect can be confirmed even when two or more kinds of second group solvents are mixed with the first group solvent. In addition, the system containing no solvent other than the first solvent and the second solvent was described, but propylene carbonate, ethylene carbonate butylene carbonate, γ-
Butyrolactone, vinylene carbonate, 2 methyl-γ
-Butyrolactone, acetyl-γ-butyrolactone, γ
A high dielectric constant solvent such as valerolactone, and tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, 1,2 -Dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether-diethylene glycol dialkyl ether, triethylene glycol dialkyl ether,
Tetraethylene glycol dialkyl ether, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, butyl propyl carbonate,
Similar effects can be obtained by mixing one or more low-viscosity solvents such as dibutyl carbonate, alkyl propionate, dialkyl malonate and alkyl acetate with a mixed solvent of the first solvent and the second solvent. Was given.
Moreover, although the mixture of the first solvent and the second solvent has been described as the electrolytic solution solvent, the use of only the first solvent as the solvent reduces the high rate charge / discharge property, but the negative electrode carbon material and the electrolytic solution. The same effect was confirmed for the reaction suppressing action of the liquid. Although the positive electrode is described using LiCoO ₂ , other lithium-containing composite oxides such as LiNiO ₂ , LiMnO ₂ and LiMn ₂ O ₄ , TiO ₂ , MnO ₂ and M are used.
The same applies to other positive electrode active materials for lithium secondary batteries, as long as they can store and release lithium ions electrochemically, such as oO ₃ , V ₂ O ₅ , TiS ₂ and MoS ₂ chalcogen compounds. The effect of was confirmed.

Throughout the above-mentioned examples, examples using only one fluorine-substituted propylene carbonate have been described, but there is no problem even if two or more fluorine-substituted propylene carbonates are mixed and used in the electrolytic solution. .
Also, an example in which LiPF ₆ was used alone as the lithium salt has been described, but LiClO ₄ , LiBF ₄ , Li
Other inorganic lithium salts such as AsF ₆ , LiCl and LiBr, and LiB (C ₆ H ₅ ) ₄ and LiC (SO ₂ CF
₃ ) ₃ , LiOSO ₂ CF _{3 and} other organolithium salts may be used alone or in a mixed system of two or more kinds, LiPF
Similar effects can be used with one or more than ₆ and mixed system of LiPF ₆ was confirmed. Further, although the negative electrode carbon material has been described using the coke calcined body and the artificial graphite, it is possible to use natural graphite, an organic calcined body, or a carbon material obtained by graphitizing them, or a mixed system of two or more kinds. Even in this case, the same effect was confirmed.

[0105]

INDUSTRIAL APPLICABILITY As shown in the present invention, a carbon material capable of electrochemically absorbing and desorbing lithium ions in a negative electrode active material, and an organic electrolytic solution prepared by dissolving a lithium salt in an organic solvent having a fluorine-substituted propylene carbonate. By using it as the electrolyte solution of the lithium secondary battery using, the reaction between the negative electrode carbon material and the electrolyte solution is suppressed and the charge / discharge efficiency of the negative electrode carbon material at the beginning of the cycle is improved compared to the case of using the conventional electrolyte solution. As a result, as compared with this type of lithium battery using a conventional electrolyte, it is possible to supply a lithium battery having a large energy density, and a low viscosity solvent, especially dimethyl carbonate, One or more selected from the group consisting of methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate When a mixed solvent of two or more kinds is used, it is possible to supply a lithium secondary battery excellent in high rate charge / discharge characteristics in addition to the above effects, and further, a fluorine-substituted propylene carbonate is mixed with another solvent. When used as a mixture, it is possible to supply a lithium secondary battery in which the above effects coexist at a particularly high level by defining the mixing ratio, and in addition, unlike ethylene carbonate, fluorine-substituted propylene carbonate is a liquid at room temperature. Since it is easy to handle, its industrial utility value is extremely high.

Particularly, the effect of the present invention is more effective as the crystallinity of the negative electrode carbon material is higher.

Claims (3)

[Claims] 1. A negative electrode having an active material of one or more selected from the group consisting of carbon materials capable of electrochemically absorbing and releasing lithium ions, and electrochemically absorbing and releasing lithium ions. In a lithium secondary battery comprising a positive electrode having as an active material one or more selected from the group consisting of possible substances, and an organic electrolytic solution, the organic electrolytic solution is at least 6 hydrogens as a solvent. A lithium secondary battery comprising one or more propylene carbonates in which one or more hydrogen is replaced by fluorine. 2. A first solvent in which the organic solvent of the organic electrolytic solution is one or two or more of propylene carbonate in which at least one hydrogen of six hydrogens is replaced by fluorine, and dimethyl carbonate and methyl ethyl. The lithium secondary battery according to claim 1, further comprising a mixed solvent with a second solvent consisting of one or more selected from the group consisting of carbonate, diethyl carbonate, methylpropyl carbonate, and methylbutyl carbonate. . 3. The volume of the first solvent is 30% or more of the total volume of the organic electrolyte solution solvent, and
The second solvent accounts for 40% or more of the total volume of the organic electrolytic solution solvent, and the volume of the mixed solvent of the first solvent and the second solvent is the entire organic electrolytic solution solvent. The lithium secondary battery according to claim 1 or 2, wherein the proportion of the product is 80% or more.