JPH09167635A - Nonaqueous electrolytic solution and nonaqueous electrolytic solution battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure adequately chemical stability. SOLUTION: (1) A nonaqueous electrolytic solution having a high withstand voltage can be obtained, by using an organic solvent containing, as an electrolyte solvent, an ester of sulfurous acid having halogen atom substituted alkyl groups expressed by the formula and, in particular, an ester of sulfurous acid having fluorine atom substituted alkyl groups. A battery in which such a nonaqueous electrolytic solution is used can generate a high voltage and is also excellent in battery characteristics. (2) In the formula, R<1> and R<2> , which may be identical or different from each other, represent for alkyl groups or halogen atom substituted alkyl groups, and at least one of the two, R<1> R<2> , represents for a halogen atom substituted alkyl group.

Description

Detailed Description of the Invention

[0001]

2. Description of the Related Art Conventionally, a battery using a non-aqueous electrolyte is
Since it has a high voltage and a high energy density and has excellent reliability such as storability, it is widely used as a power source for consumer electronic devices. As a negative electrode material for such a battery,
Alkali or alkaline earth metals have high reducing ability,
Since it is possible to obtain a battery having a high energy density, it has been used as an electrode material for a long time. Further, as the positive electrode material, LiCoO ₂ , LiNiO ₂ , LiMn ₂
Composite oxide of lithium salt such as O ₄ and transition metal, Mo
Transition metal sulfides such as S ₂ and TiS ₂ , transition metal oxides such as MnO ₂ and V ₂ O ₅ are used.

However, in a battery using an alkali metal or alkaline earth metal as a negative electrode, the metal ions in the electrolytic solution are non-uniformly deposited and dissolved on the electrode when charging and discharging are repeated, and needle-like reactivity called dendrite. In many cases, a high metal is deposited and deposited. Such dendrites fall off the electrode and lose its function as an electrode, shortening the battery life.Also, under severe conditions, the dendrite penetrates the separator that separates the positive electrode and the negative electrode, causing a local internal short circuit. It may cause a fever and cause fever.

In order to solve the problem of dendrite formation, which has been a problem of the negative electrode made of alkali metal or alkaline earth metal, a carbon material is used for the negative electrode of the battery, and LiCoO ₂ , LiNiO ₂ , for the positive electrode, A secondary battery called a rocking chair type using a composite oxide of lithium and a transition metal such as LiMn ₂ O ₄ has been studied. In this battery, lithium only moves back and forth between the carbon negative electrode and the metal oxide positive electrode in an ionic state during charging and discharging,
No dendrite is generated because it does not become metallic.
For this reason, safety has been confirmed by experiments such as overcharging, external short-circuiting, nail puncturing, and crushing. Since the safety has been improved, it has been widely spread as a consumer high-energy battery, and is rapidly spreading.

[0004]

The electrolytic solution used in the above-mentioned battery is a solution of a lithium salt dissolved in an organic solvent, and the electrolytic solution must be a negative electrode and a positive electrode in order for the battery to exhibit good performance. Need to be stable against. That is, it is an object of the present invention to provide a non-aqueous electrolyte solution that exhibits a high oxidation withstand voltage, is electrochemically stable, and improves the cycle characteristics of a battery. Another object of the present invention is to provide a non-aqueous electrolyte battery that can generate high voltage and has excellent battery characteristics.

[0005]

DISCLOSURE OF THE INVENTION In order to provide a non-aqueous electrolyte battery which is capable of safely generating a high voltage and has excellent battery characteristics, the inventors of the present invention have earnestly studied to find an electrolyte solution having a high withstand voltage. I went. As a result, they have found that the use of a non-aqueous electrolytic solution containing a halogen atom-substituted sulfite compound represented by the general formula [1] improves the withstand voltage of the electrolytic solution, and has reached the present invention.

[0006]

Embedded image

In the formula, R ¹ and R ² may be the same or different and each represents an alkyl group or a halogen atom-substituted alkyl group, at least one of which represents a halogen atom-substituted alkyl group, preferably a halogen atom-substituted alkyl group. Is a fluorine atom-substituted alkyl group. More preferably, in the general formula [1], R ¹ is —CH ₃ , —CH ₂ CH ₃ , —
_{CH2CF 3, -CH 2 CF 2 H} , -CH 2 CF 2 CF 3, -
CH ₂ CF ₂ CF ₂ H and a group selected from the group of —CH (CF ₃ ) ₂ , wherein R ² is —CH ₂ CF ₃ , —CH ₂ CF.
_{2 H, -CH 2 CF 2 CF} 3, -CH 2 CF 2 CF 2 H and -
It is preferably a group selected from the group of CH (CF ₃ ) ₂ .

Further, the non-aqueous electrolyte battery of the present invention uses the above-mentioned non-aqueous electrolyte solution as an electrolyte solution, and preferably the positive electrode contains a composite oxide of lithium and a transition metal as a main component. Consist of materials. As the electrolytic solution, an electrolytic solution containing a sulfite represented by the general formula [1] is
The decomposition of the electrolyte solvent due to oxidation does not occur easily, and the conductivity is excellent. In addition, the non-aqueous solvent battery of the present invention has excellent cycle characteristics and excellent battery characteristics.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The nonaqueous electrolytic solution of the present invention contains a sulfite compound represented by the general formula [1].

[0010]

Embedded image

In the general formula [1], R of carbonic acid ester
¹ represents an alkyl group or a halogen atom-substituted alkyl group, and R ² represents a halogen atom-substituted alkyl group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group and the like, and a methyl group or an ethyl group is particularly preferable. Examples of the halogen atom-substituted alkyl group include a fluorine atom-substituted alkyl group, a chlorine atom-substituted alkyl group, and a bromine atom-substituted alkyl group. Particularly, a fluorine atom-substituted alkyl group is preferable, and a 2,2-difluoroethyl group is preferable. , 2,2,2-trifluoroethyl group,
2,2,3,3-tetrafluoropropyl group, 2,2
Examples include a 3,3,3-pentafluoropropyl group and a 2H-hexafluoro-2-propyl group.

Examples of such sulfite include methyl sulfite-2,2-difluoroethyl group and methyl sulfite-
2,2,2-trifluoroethyl group, methyl sulfite-
2,2,3,3-tetrafluoropropyl group, methyl sulfite-2,2,3,3,3-pentafluoropropyl group, methyl sulfite-2H-hexafluoro-2-propyl group, ethyl sulfite-2,2 -Difluoroethyl group, ethyl sulfite-2,2,2-trifluoroethyl group, ethyl sulfite-2,2,3,3-tetrafluoropropyl group, ethyl sulfite-2,2,3,3,3-pentafluoro Propyl group, ethyl sulfite-2H-hexafluoro-
2-propyl group, di-2,2,2-trifluoroethyl sulfite, 2,2,2-trifluoroethyl sulfite-
2,2,3,3-tetrafluoropropyl group, sulfurous acid-
2,2,2-trifluoroethyl-2,2,3,3,3
-Pentafluoropropyl, sulfite-2,2,2-trifluoroethyl-2H-hexafluoro-2-propyl group and the like can be mentioned. These sulfites can be used as an electrolyte solution solvent by mixing one or more of the above.

The electrolyte solution solvent may be such a sulfite ester alone, but the solubility of the electrolyte is increased by using a mixed solvent with a cyclic ester carbonate such as propylene carbonate or a high dielectric constant solvent such as γ-butyrolactone or sulfolane. It is possible to improve the electric conductivity. As the cyclic carbonic acid ester, a carbonic acid ester of a 5-membered ring can be used, but a carbonic acid ester of a 5-membered ring is preferable, and ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate are particularly preferable.

When used as a mixed solvent of the above-mentioned sulfite ester and such cyclic ester carbonate, the proportion of the sulfite ester is preferably 10% by volume or more with respect to the entire solvent. Further, in order to obtain high conductivity as the electrolyte solution solvent, it is effective to use not only a high dielectric constant solvent such as the above-mentioned cyclic carbonic acid ester but also a low viscosity solvent having a high ion transfer rate. For example, to the mixed solvent of sulfite ester and cyclic carbonic acid ester described above, a nonaqueous solvent such as an ether type, a chain ester type, a chain carbonic acid ester type, etc., which is used as a normal electrolyte solvent for a battery, may be appropriately added. As a result, the viscosity of the electrolytic solution can be reduced and the electrical conductivity can be increased. In particular, a chain ester is desirable because it has a high withstand voltage and excellent oxidation resistance, and examples of such a chain ester include dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. Also in this case, the proportion of sulfite is 10% by volume based on the whole solvent.
It is desirable to make the above.

As the electrolyte that dissolves in such an electrolyte solution solvent, an electrolyte that is used in an ordinary battery electrolyte solution can be used, and LiPF ₆ , LiBF ₄ , LiAsF ₆ ,
LiCF ₃ SO ₃ , LiN (SO ₂ CF ₅ ) ₂ , LiC (S
Lithium salts such as O ₂ CF ₃ ) ₃ , LiAlCl ₃ and LiSiF ₆ are desirable, and LiPF ₆ and LiBF ₄ are particularly desirable.

The concentration at which the electrolyte is dissolved in the solvent is 0.
It can be carried out at 1 to 3 mol / l, preferably 0.5 to 1.5 mol / l. The non-aqueous electrolyte battery of the present invention uses the above-mentioned non-aqueous electrolyte solution as an electrolyte solution, and as the negative electrode material, a metal material such as an alkali metal or an alkaline earth metal, a metal sulfide and various carbon materials. However, a carbon material that can be doped with and dedoped with lithium ions is particularly desirable. Examples of such a carbon material include graphite (graphite), amorphous carbon, carbon black, and carbon fiber.

Further, as the positive electrode material, MoS ₂ , Ti
Transition metal sulfides such as S _2, transition metal oxides such as MnO _2, V ₂ O _5, or LiCoO _2, LiMnO _2, LiMn
_A composite oxide composed of lithium and a transition metal such as ₂ O ₄ or LiNiO ₂ can be used. In particular, the effect of the present invention is exerted in the case of a composite oxide composed of lithium and a transition metal having a high electromotive voltage.

In the present invention, the shape and form of the battery are not particularly limited, and various shapes and forms such as a cylinder type, a square type, a coin type, a card type and a large size can be adopted. The non-aqueous electrolyte battery of the present invention has excellent cycle characteristics, can generate high voltage, and has excellent battery characteristics.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples. 1. Measurement of oxidative withstand voltage As an electrolyte, ditrifluoroethyl sulfite (DTFE)
Lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte is dissolved in SU (abbreviated as SU) at 25 ° C. until saturated (about 0.5
mol / l) to prepare 25 ml of electrolytic solution (Example 1). In addition, methyl trifluoroethyl sulfite (MTF
An electrolyte solution was prepared by dissolving LiPF ₆ in 1 mol / l in ESU) (Example 2).

The above electrolytic solution was placed in a three-electrode type counter-voltage measuring cell using platinum for the working electrode and the counter electrode and lithium metal for the reference electrode, and a potentiogalvanostat was used for 50 m.
The electric potential was applied at 25 ° C. for V / sec. The voltage (Li / Li ⁺ ) at which the oxidative decomposition current did not flow was defined as the oxidation withstand voltage. As a comparative example, an electrolytic solution was prepared by dissolving LiPF ₆ in 1 mol / l in dimethyl sulfite (abbreviated as DMSU) (Comparative Example 1). Table 1 shows the measurement results.

[0021]

[Table 1]

From Table 1, the electrolyte solution of the sulfite ester having a fluorine atom-substituted alkyl group of Example 1 (and Example 2) is the DMS of sulfite ester having only an alkyl group.
It can be seen that the withstand voltage is higher than U and is less likely to be oxidized. 2. Measurement of electric conductivity As an electrolyte, ditrifluoroethyl sulfite (DTFE)
Volume ratio of SU) to propylene carbonate (abbreviated as PC) 1:
LiPF ₆ dissolved in 1 mol / l in the mixed solvent of 1 was used (Example 3). The electric conductivity of this electrolytic solution was measured at 25 ° C. and 10 kHz using an impedance meter.

As Comparative Example 2, P which is a general electrolytic solution
The electrical conductivity was measured in the same manner as in Example 3 using an electrolytic solution containing a mixed solvent of C and diethyl carbonate (abbreviated as DEC) in a volume ratio of 1: 1. Table 2 shows the results.

[0024]

[Table 2]

From Table 2, it can be seen that the electrolytic solution of the present invention exhibits a practical level of electrical conductivity. 3. Battery performance The battery size as shown in Fig. 1 is 20 mm in outer diameter and 2.5 in height.
A mm-shaped non-aqueous electrolyte battery was prepared. For the negative electrode 1, lithium metal was used, and for the positive electrode 2, a mixture obtained by adding 85 parts by weight of LiCoO ₂ to 12 parts by weight of graphite as a conductive agent and 3 parts by weight of a fluororesin as a binder was used, which was pressure-molded. The substances forming the negative electrode 1 and the positive electrode 2 are respectively pressure-bonded to the negative electrode can 4 and the positive electrode can 5 via the porous separator 3 made of polypropylene. As an electrolyte for such a battery, 1 mol of LiPF ₆ is mixed with a solvent in which PC and DTFESU are mixed at a volume ratio of 1: 1.
/ L was used as a melted solution, and the solution was sealed with a sealing gasket 6 (Example 4).

The battery thus prepared was charged with a constant current and a constant voltage of 1.0 mA for 10 hours with an upper limit voltage of 4.2 V, and then 3.0 at a constant current of 1.0 mA.
The cycle of discharging until V was repeated. FIG. 2 shows the results, and is a plot of the capacity retention ratio with respect to the number of cycles when the initial capacity is 100%.

As an electrolyte solvent, PC / MTFES
U (volume ratio 1: 1) (Example 5), PC / DMSU (volume ratio 1: 1) (Comparative Example 3), PC / DEC (volume ratio 1:
1) The same experiment was performed on a coin battery prepared in the same manner as the above battery except that (Comparative Example 4) was used. The results are shown together in FIG. As is clear from FIG. 2, the battery using the electrolytic solution according to the present example has a high withstand voltage and low reactivity with lithium, and thus exhibits excellent cycle characteristics.

[0028]

As described above, the non-aqueous electrolytic solution of the present invention uses an organic solvent containing a sulfite ester having a halogen atom-substituted alkyl group, particularly a sulfite ester having a fluorine atom-substituted alkyl group as an electrolytic solution solvent. Therefore, it has a high withstand voltage and exhibits sufficient electric conductivity. Therefore, the battery of the present invention using such an electrolytic solution has excellent cycle characteristics, can generate high voltage, and is excellent in battery characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a battery according to the present invention.

FIG. 2 is a diagram showing the performance of a battery according to an embodiment of the present invention.

[Explanation of symbols]

 1 ... Negative electrode 2 ... Positive electrode

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeru Fujita 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Atsoo Komaru 6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (7)

[Claims] 1. A non-aqueous electrolytic solution containing a sulfite compound represented by the general formula [1]. Embedded image (In the formula, R ¹ and R ² may be the same or different and each represents an alkyl group or a halogen atom-substituted alkyl group, and at least one R ² represents a halogen atom-substituted alkyl group.) 2. In the general formula [1] according to claim 1, R is
^2. The non-aqueous electrolyte solution according to claim ¹ , wherein at least one of ¹ and R ² is a fluorine atom-substituted alkyl group. 3. In the general formula [1] according to claim 1, R is
¹ _{-CH 3, -CH 2 CH 3,} -CH2CF 3, -CH 2 C
_{F 2 H, -CH 2 CF 2} CF 3, -CH 2 CF 2 CF 2 H and -CH (CF ₃₎ a group selected from the _second group, R ² is -CH ₂ CF _3, -CH _{2 CF 2 H, -CH 2 CF 2} CF 3,
Nonaqueous electrolytic solution according to claim 2, wherein it is a group selected from -CH ₂ CF ₂ CF ₂ H and -CH (CF _{3) 2} groups. 4. In the general formula [1] according to claim 1, R is
The non-aqueous electrolyte according to claim ^1, wherein ¹ and R ² are —CH ₂ CF ₃ . 5. The non-aqueous electrolytic solution according to claim 1, which contains the sulfite compound represented by the general formula [1] in an amount of 10% by volume or more of the electrolytic solution solvent. 6. A non-aqueous electrolyte battery using the non-aqueous electrolyte according to any one of claims 1 to 5. 7. The non-aqueous electrolyte battery according to claim 6, further comprising a positive electrode containing a composite oxide of lithium and a transition metal as a main component.