JP2003031259A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

[PROBLEMS] To improve the cycle characteristics of a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode containing a carbon material capable of inserting and extracting lithium, and a nonaqueous electrolyte. A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode including a carbon material capable of inserting and extracting lithium, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is vinylene carbonate. And vinyl ethylene carbonate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery having excellent cycle characteristics.

[0002]

2. Description of the Related Art Carbon materials such as coke and graphite are non-aqueous electrolytes that can replace metallic lithium because they are excellent in flexibility and there is no risk of internal short circuit due to the growth of dendritic lithium. Widely used as a negative electrode material for secondary batteries.

By the way, it is known that in a battery using a carbon material as a negative electrode material, the battery characteristics greatly change depending on the type of the non-aqueous electrolyte solution. For example, as the solvent, ethylene carbonate, dimethyl carbonate or vinylene carbonate is used. By using carbonic acid ester such as
It is known that the electrochemical characteristics of the carbon material can be sufficiently exhibited. However, on the other hand, when a carbon material is used as a negative electrode material and a carbonic acid ester is used as a solvent for a non-aqueous electrolyte, the solvent decomposes with gas generation, and the battery capacity increases as the charge / discharge cycle progresses. It is known that there is a problem of gradually decreasing.

Therefore, in order to solve such a problem, a method of adding vinylene carbonate or vinyl ethylene carbonate to the electrolytic solution has been proposed. For example,
Addition of vinyl ethylene carbonate to a carbonate ester electrolyte mainly composed of ethylene carbonate (EC) is disclosed in JP-A-6-84542 and JP-A-8-45545. Further, JP-A-4-87156 proposes to use vinyl ethylene carbonate in a non-aqueous electrolyte battery using lithium metal for the negative electrode.

[0005]

In the non-aqueous electrolyte secondary battery, improving the cycle characteristics and suppressing the deterioration of the initial characteristics for a long period of time is still a major issue in development. Even when such a method is used, satisfactory cycle characteristics have not yet been obtained.

An object of the present invention is to improve the cycle characteristics of a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a carbon material capable of inserting and extracting lithium, and a non-aqueous electrolyte solution. To do.

[0007]

The invention of claim 1 provides a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a carbon material capable of inserting and extracting lithium, and a non-aqueous electrolytic solution. The non-aqueous electrolyte solution contains vinylene carbonate and vinyl ethylene carbonate.

According to the invention of claim 1, the cycle characteristics of the non-aqueous electrolyte secondary battery are improved by including both vinylene carbonate and vinyl ethylene carbonate in the electrolytic solution.

According to a second aspect of the present invention, in the non-aqueous electrolyte secondary battery according to the first aspect, the non-aqueous electrolyte contains a cyclic carbonic acid ester and a chain carbonic acid ester, and all electrolysis except vinylene carbonate and vinyl ethylene carbonate. The content of vinylene carbonate is 0.01% by mass or more and 5% by mass or less, and the content of vinyl ethylene carbonate is 0.01% by mass or more and 2% by mass or less with respect to the liquid solvent. To do.

According to the second aspect of the present invention, the decomposition and degradation of the carbonic acid ester is suppressed, and the cycle characteristics of the non-aqueous electrolyte secondary battery are remarkably improved.

According to a third aspect of the present invention, in the non-aqueous electrolyte secondary battery according to the first or second aspect, the cyclic carbonate content is 20% by volume with respect to all the electrolyte solution solvents other than vinylene carbonate and vinyl ethylene carbonate. % Or more and 50% by volume or less.

The invention of claim 4 is the invention of claim 1, 2 or 3.
In the described non-aqueous electrolyte secondary battery, the chain carbonic acid ester is at least one selected from dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

According to the invention of claim 3 or 4,
The improvement of the cycle characteristics of the non-aqueous electrolyte secondary battery becomes remarkable.

According to a fifth aspect of the invention, in the non-aqueous electrolyte secondary battery according to the first, second, third or fourth aspect, the carbon material has a (002) plane spacing: d value (d002) of 3.37Å.
It is characterized by the following.

According to the invention of claim 5, the use of high crystalline carbon for the negative electrode makes the cycle characteristics of the non-aqueous electrolyte secondary battery more significantly improved.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention realizes improvement of cycle characteristics by including both vinylene carbonate and vinyl ethylene carbonate in a non-aqueous electrolyte.

As the organic solvent that constitutes the non-aqueous electrolyte,
For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, acetic ester compound, dimethoxyethane, diethoxyethane, tetrahydrofuran, etc. may be used alone or in combination of two or more. It is preferable that the carbonic acid ester other than vinylene carbonate and vinyl ethylene carbonate is included, and particularly in the case of the non-aqueous electrolyte secondary battery of the present invention, it is preferable to use a cyclic carbonic acid ester and a chain carbonic acid ester as a mixture. . When such an organic solvent is contained, the effect of improving the cycle characteristics in the non-aqueous electrolyte secondary battery becomes remarkable.

When a mixed solvent of vinylene carbonate, vinylethylene carbonate and carbonic acid ester is used, vinylene carbonate and vinylethylene carbonate are likely to exist in the vicinity of the negative electrode, so that the easily decomposable carbonic acid ester is difficult to approach the negative electrode. It is considered that, as a result, decomposition degradation of the carbonate ester is suppressed.

The content of vinylene carbonate and vinyl ethylene carbonate in the organic electrolytic solution may be appropriately adjusted according to the composition of the non-aqueous electrolytic solution, but the total content excluding vinylene carbonate and vinyl ethylene carbonate may be adjusted. The content of vinylene carbonate is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.25% by mass or more and 2% by mass with respect to the electrolytic solution solvent (which is 100% by mass).
The content of vinyl ethylene carbonate is preferably 0.01% by mass or more and 2% by mass or less,
More preferably, it is 0.25 mass% or more and 1 mass% or less. If these are too small, it will not be effective,
In the case of too much vinylene carbonate,
This is because the high-rate discharge characteristics are particularly poor, and in the case of vinyl ethylene carbonate, the swelling of the battery is large.

Further, in the non-aqueous electrolyte secondary battery of the present invention, all the electrolyte solvent except vinylene carbonate and vinyl ethylene carbonate (this is 100% by volume).
On the other hand, the cyclic carbonate content is 20% by volume or more and 5
It is preferable to set it to 0% by volume or less. In particular, ethylene carbonate is preferably used as the cyclic carbonic acid ester, and the cycle characteristics are remarkably improved. The high rate discharge characteristics can be improved by defining the content of the cyclic carbonic acid ester. Even in such a case, another solvent may be further mixed and used.

As the chain ester carbonate, it is particularly preferable to use at least one selected from dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

As the carbon material capable of occluding and releasing lithium used for the negative electrode, various materials capable of occluding and releasing lithium such as natural graphite, artificial graphite, coke, non-graphitizable carbon, and pyrolytic resin can be used. In particular, it is preferable to use a carbon material having a (002) plane spacing: d value (d002) of 3.37 Å or less. This is because the effect of the present invention is remarkable when such a carbon material having relatively high crystallinity is used. Examples of such a carbon material having high crystallinity include graphites (natural graphite and artificial graphite, those modified and modified), and the crystallinity is increased by, for example, high pressure treatment so that the d002 value is set to 3.37Å or less. There is modified coke.

In the non-aqueous electrolyte secondary battery of the present invention, other battery constituent materials such as the positive electrode material and the solute of the non-aqueous electrolyte solution have been proposed or put into practical use for non-aqueous electrolyte secondary batteries. It is possible to use the above materials without particular limitation.

For example, as the positive electrode material, the composition formula Lix is used.
MO ₂ , or LiyM ₂ O ₄ (M is one or more transition metals, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), a complex oxide, an oxide having tunnel-shaped holes, and a layered structure Inorganic compounds capable of occluding and releasing lithium, such as the metal chalcogenide, can be used. As a specific example, LiC
oO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂
O ₄ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , T
Examples thereof include iO ₂ and TiS ₂ . Further, an organic compound such as a conductive polymer such as polyaniline can be used. Further, the above various active materials can be mixed and used regardless of whether they are inorganic compounds or organic compounds.

Further, for example, as lithium salts dissolved in an organic solvent, LiPF ₆ , LiClO ₄ , LiBF ₄ ,
LiAsF ₆ , LiCF ₃ CO ₂ , LiCF ₃ SO ₃ ,
_{LiN (SO 2 CF 3) 2} , LiN (SO 2 CF 2 CF
₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (COC
Salts such as F ₂ CF ₃ ) ₂ can be used alone or in combination.

[0026]

The present invention will be described in more detail based on the following examples.

[Example 1] A positive electrode plate was obtained by holding spinel manganese composite oxide particles as a positive electrode active material on a current collector made of an aluminum foil having a thickness of 20 µm. The positive electrode plate is polyvinylidene fluoride 8 which is a binder.
% By mass and 4% by mass of acetylene black as a conductive agent together with 88% by mass of the active material, and N-methylpyrrolidone was added to prepare a paste, and then applied to both surfaces of the current collector material, and then 150 It was prepared by drying at 0 ° C. for 2 hours.

The negative electrode plate was prepared by mixing 92 parts by weight of artificial graphite powder and 8 parts by weight of polyvinylidene fluoride as a binder on both sides of a current collector made of a copper foil having a thickness of 14 μm and adding N-methylpyrrolidone. In addition, it was prepared by applying and drying a paste prepared.

As the non-aqueous electrolyte, 30% by volume of ethylene carbonate (EC) and dimethyl carbonate (DM) are used.
C) 0.5% by mass of vinylene carbonate (VC) and 0.3% by mass of vinylethylene carbonate (VEC) were added to a mixed solvent of 70% by volume, and LiP was further added.
F ₆ was dissolved at a ratio of 1 M (mol / liter) to prepare a non-aqueous electrolytic solution.

A prismatic battery MA1 of the present invention was produced using the positive and negative electrodes and the non-aqueous electrolyte described above. A polypropylene microporous film was used as the separator.

FIG. 1 is a schematic sectional view of the produced battery MA1 of the present invention. In FIG. 1, 1 is a non-aqueous electrolyte secondary battery,
Reference numeral 2 is a wound electrode group, 3 is a positive electrode, 4 is a negative electrode, 5 is a separator, 6 is a battery case, 7 is a battery lid, 8 is a safety valve, 9 is a positive electrode terminal, and 10 is a positive electrode lead wire. The wound electrode group 2 is housed in a battery case 6 together with an electrolytic solution (not shown), a safety valve 8 is provided in the battery case 6, and the battery lid 7 and the battery case 6 are sealed by laser welding. Positive terminal 9
Is connected to the positive electrode 3 via the positive electrode lead wire 10, and the negative electrode 4
Are connected by contact with the inner wall of the battery case 6.

[Example 2] Ethylene carbonate (E
C) 30% by volume, diethyl carbonate (DEC) 70
0.5% by mass of vinylene carbonate (VC) and 0.3% by mass of vinylethylene carbonate (VEC) were added to the mixed solvent consisting of 1% by volume, and 1 more LiPF ₆ was added.
A prismatic practical battery MA2 was produced in the same manner as in Example 1 except that the nonaqueous electrolytic solution prepared by dissolving at a ratio of M (mol / liter) was used.

[Example 3] Ethylene carbonate (E
C) 30 volume%, diethyl carbonate (DEC) 0 volume%, dimethyl carbonate (DMC) 40 volume% mixed solvent, vinylene carbonate (VC)
0.5% by mass and vinyl ethylene carbonate (VEC)
In addition to 0.3% by mass, LiPF ₆ was further added to 1 M (mol / mol
A rectangular practical battery MA3 was produced in the same manner as in Example 1 except that the non-aqueous electrolyte solution prepared by dissolving in a proportion of 1 liter) was used.

[Comparative Example 1] Ethylene carbonate (E
C) 30% by volume, dimethyl carbonate (DMC) 70
A rectangular comparative battery CA1 was produced in the same manner as in Example 1 except that a nonaqueous electrolytic solution obtained by dissolving LiPF ₆ in a mixed solvent of volume% at a ratio of 1 M (mol / liter) was used.

[Comparative Example 2] Ethylene carbonate (E
C) 30% by volume, diethyl carbonate (DEC) 70
A rectangular comparative battery CA2 was produced in the same manner as in Example 1 except that a nonaqueous electrolytic solution obtained by dissolving LiPF ₆ in a mixed solvent of volume% at a ratio of 1 M (mol / liter) was used.

[Comparative Example 3] Ethylene carbonate (E
C) 30% by volume, diethyl carbonate (DEC) 30
1M (mol / liter) of LiPF ₆ in a mixed solvent consisting of 40% by volume of dimethyl carbonate (DMC)
Inventive batteries MA1, MA2, MA3 and comparative batteries CA1, C3 were prepared in the same manner as in Example 1 except that a nonaqueous electrolytic solution obtained by melting was used in the following manner.
A2, CA3 (The discharge capacity at the beginning of the cycle is 38
0 mAh), the first cycle was charged and discharged under the following conditions. Charging: 380 mA constant current / 4.
1V constant voltage × 5 h (25 ° C.), discharge: 380 mA constant current, final constant voltage 2.75 V (25 ° C.). Next, a cycle test was performed from the second cycle to the 399th cycle under the following conditions. Charging: 380mA constant current / 4.1
V constant voltage x 5h (45 ° C), discharge: 380mA constant current,
Final constant voltage 2.75V (45 ° C). Furthermore, the 400th cycle of charging and discharging was performed under the following conditions. Charge: 38
0 mA constant current / 4.1 V constant voltage × 5 h (25 ° C.), discharge: 380 mA constant current, end constant voltage 2.75 V (25
C). Therefore, the capacity deterioration rate at the 400th cycle is defined as follows and shown in Table 1.

Capacity deterioration rate at 400th cycle = (discharge capacity at 1st cycle−discharge capacity at 400th cycle) /
(Discharge capacity in the first cycle)

[0038]

[Table 1]

As shown in Table 1, the batteries of the present invention MA1 and M1
The capacity deterioration rates of the A2 and MA3 at the 400th cycle were both small at about 20%, while the comparative batteries CA1 and
The capacity deterioration rates at the 400th cycle of CA2 and CA3 were as large as 30%. From this, it is found that the decrease in discharge capacity due to the decomposition of the non-aqueous electrolyte during the charge / discharge cycle is suppressed by containing both vinylene carbonate (VC) and vinyl ethylene carbonate (VEC). It was

Next, the relationship between the volume mixing ratio of ethylene carbonate (EC) and the cycle characteristics was investigated. Ethylene carbonate (EC) and diethyl carbonate (DE
The volume mixing ratio of C) is 10:90, 20:80, 30 :.
70, 40:60, 50:50, 60:40, 80: 2
To the mixed solvent consisting of 0, 0.50% by mass of vinylene carbonate (VC) and 0.3% by mass of vinylethylene carbonate (VEC), respectively, and further added LiPF
Example batteries 4 to 7 and comparative example batteries 4 to 6 of the present invention were produced in the same manner as in Example 1 except that a nonaqueous electrolytic solution prepared by dissolving ₆ at a ratio of 1 M (mol / liter) was used. did. Then, a charge / discharge cycle test was performed under the same conditions as above to determine the capacity deterioration rate at the 400th cycle of each battery, and the relationship between the volume mixing ratio of ethylene carbonate and the cycle characteristics was investigated. The results are shown in Table 2.

[0041]

[Table 2]

As shown in Table 2, when the proportion of ethylene carbonate (EC) is 20 to 50% by volume, the capacity deterioration rate can be made particularly small, and the non-aqueous electrolytic solution exhibiting excellent cycle characteristics. It was found that a secondary battery could be obtained.

Furthermore, the relationship between the volume characteristics of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC) and the cycle characteristics was investigated. Ethylene carbonate (EC) 30% by volume, dimethyl carbonate (DM
C) Vinylene carbonate (VC) and vinyl ethylene carbonate (VE
The mixing volume ratio of C) is 0: 0, 0.075: 0.07
5, 0.075: 1.5, 1.5: 0.075, 0.
Example 6 except that a non-aqueous electrolyte solution prepared by dissolving LiPF ₆ at a ratio of 1M (mol / liter) was used in addition to 6: 0.6, 1.5: 1.5 and 2: 2. Similarly, Example batteries 8 to 12 of the present invention and Comparative example battery 7
10 were produced. Then, a charge / discharge cycle test was performed under the same conditions as above to obtain the capacity deterioration rate at the 400th cycle of each battery, and the relationship between the volume mixing ratio of vinylene carbonate (VC) and vinylethylene carbonate (VEC) and the cycle characteristics. Was examined and the results are shown in Table 3.

[0044]

[Table 3]

As shown in Table 3, vinylene carbonate (VC) and vinyl ethylene carbonate (VE
For an electrolytic solution consisting of a cyclic carbonic acid ester and a chain carbonic acid ester excluding C), vinylene carbonate (V
When the content of C) is 0.01% by mass or more and 5% by mass or less and the content of vinyl ethylene carbonate (VEC) is 0.01% by mass or more and 2% by mass or less, capacity deterioration is caused. It was found that the rate can be made particularly small and a non-aqueous electrolyte secondary battery exhibiting excellent cycle characteristics can be obtained.

The mixed solvent before the addition of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC) is a mixed solvent consisting of 30% by volume of ethylene carbonate (EC) and 70% by volume of dimethyl carbonate (DMC). Instead of, a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC), 30% by volume of ethylene carbonate (EC), 30% by volume of diethyl carbonate (DEC), and 40% of dimethyl carbonate (DMC) Similar results were obtained when a mixed solvent of volume% was used.

[0047]

INDUSTRIAL APPLICABILITY The present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a carbon material capable of inserting and extracting lithium, and a non-aqueous electrolyte solution. It is characterized by containing carbonate and vinyl ethylene carbonate. According to the present invention, it is possible to manufacture a battery in which the decomposition degradation of carbonate ester is suppressed, the rate of capacity deterioration accompanying the progress of charge / discharge cycles is small, and the cycle characteristics are excellent.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a prismatic battery MA1 of the present invention.

[Explanation of symbols]

1 Non-aqueous electrolyte secondary battery 2 winding type pole group 3 positive electrode 4 Negative electrode 5 severs 6 battery case

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode containing a carbon material capable of inserting and extracting lithium, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is vinylene carbonate. And a non-aqueous electrolyte secondary battery containing vinyl ethylene carbonate. 2. The non-aqueous electrolytic solution contains a cyclic carbonic acid ester and a chain carbonic acid ester, and for all electrolytic solution solvents except vinylene carbonate and vinyl ethylene carbonate,
Content of vinylene carbonate is 0.01% by mass or more 5
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of vinyl ethylene carbonate is 0.01% by mass or more and 2% by mass or less. 3. The non-volatile polymer according to claim 1, wherein the content of the cyclic carbonic acid ester is 20% by volume or more and 50% by volume or less based on the total amount of the electrolyte solvent except vinylene carbonate and vinylethylene carbonate. Water electrolyte secondary battery. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the chain ester carbonate is at least one selected from dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. 5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the carbon material has a (002) plane spacing: d value (d002) of 3.37 Å or less. .