JP2000285962A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To improve cycle characteristics, load characteristics, and low-temperature characteristics of a non-aqueous electrolyte secondary battery. SOLUTION: An anode made of a carbon material capable of doping / dedoping lithium, a cathode made of a composite oxide of lithium and one or more transition metals, and an electrolyte dissolved in a non-aqueous solvent A non-aqueous electrolyte secondary battery comprising: a non-aqueous electrolyte;
Oxazolidone is contained in the range of 0.05% by volume or more and less than 1% by volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery having improved initial characteristics, cycle characteristics, low-temperature characteristics, and load characteristics by using a specific non-aqueous solvent. The present invention relates to a water electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices such as camera-integrated video tape recorders, mobile phones, and laptop computers have been rapidly becoming smaller, lighter and more portable. Therefore, there is a demand for a lightweight and high capacity secondary battery as a power supply for these electronic devices.

Examples of the secondary battery include a conventionally used lead secondary battery, a nickel-cadmium secondary battery, and a recently proposed non-aqueous electrolyte secondary battery. Among them, non-aqueous electrolyte secondary batteries have advantages such as light weight, high energy density, high voltage generation, high safety, and no pollution, and further improved characteristics. R & D is being actively pursued to achieve the goal.

The above non-aqueous electrolyte secondary battery comprises a negative electrode capable of doping / dedoping lithium, a positive electrode and a non-aqueous electrolyte in which a lithium salt is dissolved as an electrolyte in a non-aqueous solvent. It has a basic configuration.

The positive electrode active material is, for example, a lithium transition metal composite oxide, and the negative electrode active material is lithium metal, a lithium alloy, or a carbon material capable of doping / dedoping lithium. And the like. Among them, the carbon material of the negative electrode active material is expected to improve the cycle characteristics of the battery. Among carbon materials, graphite materials are expected to improve the energy density per unit volume.

[0006]

In the above-described non-aqueous electrolyte secondary battery, the selection of the positive electrode and the negative electrode is of course important, but in order to obtain good battery characteristics, it is responsible for transferring lithium ions. The choice of non-aqueous electrolyte is also important.

As the non-aqueous solvent constituting the non-aqueous electrolyte, a combination of a high-dielectric solvent having a high ability to dissolve an electrolyte and a low-viscosity solvent having a high ability to transport electrolyte ions is usually used. For example, propylene carbonate (PC) as a high dielectric constant solvent, 1,2-dimethoxyethane (DME), 2-methyltetrahydrofuran (2-MeTHF), and methyl propionate (M
P), ethyl propionate (EP), methyl butyrate (M
B), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DE
A propylene carbonate-based electrolytic solution obtained by mixing C) and the like has a higher conductivity, and has an advantage of improving the cycle characteristics of a battery.

[0008] However, the propylene carbonate-based electrolyte solution is superior in characteristics to other solvents proposed so far, but in order to meet the recent demand for characteristics for secondary batteries, the characteristics are further improved. Is required.

Further, it has been pointed out that non-aqueous electrolyte secondary batteries using a graphite material as a negative electrode have a problem that the battery characteristics are deteriorated because propylene carbonate used as a solvent is decomposed in a charging process. Yes (J. Elect
roanal. Chem. 219, 273, (1987)).

As a method for addressing this problem, a solvent such as ethylene carbonate (EC) which is difficult to decompose in the charging process may be used instead of propylene carbonate (PC). Thus, it is known that decomposition of the electrolytic solution is suppressed, and the graphite material can be used as a negative electrode of the nonaqueous electrolyte secondary battery.
However, studies by the inventors so far have revealed that in the case of a nonaqueous electrolyte secondary battery using ethylene carbonate as a solvent, sufficient cycle characteristics, load characteristics, and low-temperature characteristics cannot be obtained.

The present invention has been proposed in view of such prior art, and provides a non-aqueous electrolyte secondary battery having high energy density and improved cycle characteristics, load characteristics, and low-temperature characteristics. With the goal.

[0012]

Means for Solving the Problems As a result of repeated investigations to achieve the above object, the present inventor has found that 3-methyl-2-oxazolidone (OZ) represented by the following formula (2) as a nonaqueous solvent for an electrolytic solution. ) Was found to be effective.

[0013]

Embedded image

3-methyl-2-oxazolidone (OZ)
About 3-methyl- for non-aqueous electrolyte secondary batteries
A report using 2-oxazolidone (OZ) has been previously proposed (Japanese Patent Laid-Open No. 8-321213). However, the present inventor has found that the use of a solvent containing 3-methyl-2-oxazolidone (OZ) in a range of 0.05 vol% or more and less than 1 vol% particularly in a battery using a carbon material as a negative electrode, It has been found that the initial discharge capacity can be improved, and the cycle characteristics, load characteristics, and low-temperature characteristics can also be improved, and the present invention has been completed.
Therefore, the present invention has been completed based on such findings, and a negative electrode made of a carbon material capable of doping and undoping lithium and a composite oxide of lithium and one or more transition metals are provided. In a non-aqueous electrolyte secondary battery comprising a positive electrode made of a material and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, the non-aqueous solvent contains 3-methyl-2-oxazolidone at 0.05%. It is characterized in that it is contained in the range of at least volume% and less than 1 volume%.

[0015]

Embodiments of the present invention will be described below in detail.

Further, the present invention is not limited to the following examples, and it goes without saying that the present invention can be arbitrarily changed without departing from the gist of the present invention.

FIG. 1 is a longitudinal sectional view showing one configuration example of the nonaqueous electrolyte battery of the present invention. This non-aqueous electrolyte secondary battery
A negative electrode 1 formed by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode 2 formed by applying a positive electrode active material to a positive electrode current collector 10 include:
The wound body wound in close contact with the separator 3 is
It is loaded inside the battery can 5.

The negative electrode 1 is manufactured by applying a negative electrode mixture containing a negative electrode active material and a binder on a negative electrode current collector 9 and drying.

As the negative electrode current collector 9, a metal foil such as a copper foil, a nickel foil, and a stainless steel foil is used.

These metal foils are preferably porous metal foils. By making the metal foil a porous metal foil, the adhesive strength between the current collector and the electrode layer can be increased. As such a porous metal foil, in addition to a punching metal and an expanded metal, a metal foil having a large number of openings formed by etching can be used.

As the negative electrode active material, it is preferable to use a carbon material capable of doping and undoping lithium. As a carbon material that can be doped and dedoped with lithium, for example, a carbon material such as a non-graphitizable carbon-based material and a graphite-based material can be used. Specifically, carbon materials such as pyrolytic carbons, cokes, graphites, glassy carbon fibers, fired organic polymer compounds, carbon fibers, and activated carbon can be used. Examples of the coke include pitch coke, needle coke, and petroleum coke. The fired organic polymer compound is obtained by firing a phenol resin, a furan resin or the like at an appropriate temperature and carbonizing the same. And, among the above carbon materials, the (002) plane spacing is 0.340.
nm or less, the crystallite thickness in the C-axis direction is 16.0 nm or more,
Graphite having a crystal structure with a G value in a Raman spectrum of 2.5 or more and a true density of 2.1 g / cm ³ or more can be more preferably used. The (002) plane spacing is 0.340 nm or less, and the crystallite thickness in the C-axis direction is 1
G value in Raman spectrum is not less than 6.0 nm.
This is because graphite having a crystal structure having a crystal density of 5 or more and a true density of 2.1 g / cm ³ or more can improve the energy density per unit volume because of its high density. Where G
The value indicates a ratio between the signal intensity derived from the graphite structure of the carbon material and the signal intensity derived from the non-crystalline structure in the Raman spectrum, and serves as an index of a microscopic crystal structure defect.

In forming a negative electrode using the above-described negative electrode active material, a known conductive agent or binder can be added.

The positive electrode 2 is manufactured by applying a positive electrode mixture containing a positive electrode active material and a binder on a positive electrode current collector 10 and drying the mixture.

As the positive electrode current collector 10, a metal foil such as an aluminum foil, a nickel foil, and a stainless steel foil is used. These metal foils are preferably porous metal foils. By making the metal foil a porous metal foil, the adhesive strength between the current collector and the electrode layer can be increased. As such a porous metal foil, in addition to a punching metal and an expanded metal, a metal foil having a large number of openings formed by etching can be used.

As the positive electrode active material, it is preferable to use an active material mainly composed of a composite oxide composed of lithium and one or more transition metals from the viewpoint of improving the battery capacity and increasing the energy density. Examples of such an active material include Li _x M
O ₂ (wherein M is preferably one or more transition metals,
0.05 ≦ x ≦ 1.10. ) Is preferably used. As the lithium composite oxide, specifically, LiCoO ₂ , LiNiO ₂ , L
(wherein, x, y varies by the discharge state of the battery, usually a 0 <x <1,0.7 <y ≦ 1.) i x Ni y Co 1-y O 2, LiMn 2 O 4 and the like It is preferably used. Also,
When the transition metal M is Mn, Li _x Mn ₂ O ₄ can be used in addition to Li _x MnO ₂ .

Such a lithium composite oxide comprises lithium carbonate, nitrate, oxide or hydroxide and carbonate, nitrate, oxide or hydroxide such as cobalt, manganese or nickel. It can be prepared by pulverizing and mixing according to a desired composition and baking in a temperature range of 600 to 1000 ° C. in an oxygen atmosphere. These lithium composite oxides can generate a high voltage and become positive electrode active materials excellent in energy density.

For the positive electrode 2, these positive electrode active materials may be used alone, or a plurality of types may be mixed and used. When forming the positive electrode 2 using the above-described positive electrode active material, a known conductive agent or binder can be added.

In preparing the non-aqueous electrolyte, the non-aqueous solvent may be any of various known non-aqueous solvents conventionally used for non-aqueous electrolytes, such as 3-methyl-2 represented by the following formula (3). -Oxazolidone (OZ) can be used as a mixture.

[0029]

Embedded image

Here, a solvent having a high dielectric constant such as ethylene carbonate (EC) or propylene carbonate (PC) is used.
-Methyl-2-oxazolidone (OZ) alone may be used as a mixture, but for example, low-viscosity solvents such as 1,2-dimethoxyethane (DME), 2-methyl-tetrahydrofuran (2-MeTHF), and methyl propionate (M
P), ethyl propionate (EP), methyl butyrate (M
B), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DE
C) and the like can be further mixed and used. Among them, mixing a chain ester such as methyl propionate (MP), ethyl propionate (EP), methyl butyrate (MB), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Dimethyl carbonate (DM)
It is more preferable to mix chain carbonates such as C), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). Since a high dielectric constant solvent such as ethylene carbonate or propylene carbonate has a high ability to dissolve the electrolyte, the energy density can be increased by using these solvents. Then, (002)
When a carbon material having a plane spacing of 0.340 nm or less is used, it is preferable to use ethylene carbonate, and it is particularly preferable that the carbon material be contained in the nonaqueous solvent in a range of 5% by volume to 50% by volume.

Since the low-viscosity solvent as described above has a high ability to transport electrolyte ions, the use of such a solvent can improve the ionic conductivity. Among them, chain esters, particularly chain carbonates, can be used particularly preferably because of their great effect.

The 3-methyl-2-oxazolidone is initially mixed with the above mixed solvent of a high dielectric constant solvent and a low viscosity solvent in a range of 0.05 vol% or more and less than 1 vol%. Discharge capacity, cycle characteristics, low-temperature characteristics, and load characteristics can be improved. These effects are particularly significant in a nonaqueous electrolyte battery using a carbon material as a negative electrode. Where 3-methyl-
The reason why the mixing ratio of 2-oxazolidone to the mixed solvent of the high dielectric constant solvent and the low viscosity solvent is set to 0.05 vol% or more is that the mixing ratio is less than 0.05 vol% as described above. This is because the effect cannot be sufficiently exhibited. Further, the reason that the mixing ratio of 3-methyl-2-oxazolidone to the mixed solvent of the high dielectric constant solvent and the low viscosity solvent is less than 1% by volume is that the mixing ratio is 1% by volume or more.
This is because the initial discharge capacity and cycle characteristics are reduced.

The electrolyte to be dissolved in the non-aqueous solvent is not particularly limited, and those used in conventional non-aqueous electrolyte secondary batteries can be used.
For example, LiClO _{4 ,} LiAsF ₆ , LiPF _6, LiB
F ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) _{2 and the} like can be used. And, among them, LiPF ₆ , Li
BF _{4 and the} like are particularly preferably used because of their high conductivity.

The structure of the battery is not particularly limited, and can be applied to various shapes such as a wound shape, a laminated shape, a cylindrical shape, a square shape, a coin shape, and a button shape.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Here, cylindrical non-aqueous electrolyte secondary batteries shown in FIG. 1 were produced as examples and comparative examples.

Example 1 First, a negative electrode 1 was produced as follows.

A petroleum pitch is used as a starting material, and a functional group containing oxygen is introduced therein by 10 to 20%, and then calcined at 1000 ° C. in an inert gas stream to obtain a non-graphitizable carbon material close to glassy carbon. Was. About the obtained non-graphitizable carbon material, X
As a result of a line diffraction measurement, the (002) plane spacing was 0.376 nm, and the true density was 1.58 g / cm ³ . This non-graphitizable carbon material is pulverized to an average particle size of 10
μm carbon material powder.

Then, 90 parts by weight of the carbon material powder,
A negative electrode mixture was prepared by mixing 10 parts by weight of polyvinylidene fluoride as a binder, and further mixed with N-methyl-2.
-Dispersed in pyrrolidone to form a slurry. Then, this slurry was uniformly applied to both surfaces of a 10 μm-thick strip-shaped copper foil as the negative electrode current collector 9, dried, and then compression-molded with a roll press to produce a negative electrode 1.

Next, the positive electrode 2 was produced as follows.

Lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol: 1 mol, and calcined in air at 900 ° C. for 5 hours to obtain a positive electrode active material (LiCoO ₂ ). Then, 91 parts by weight of this LiCoO ₂ , 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture, and this was further mixed with N-methyl-2-. It was dispersed in pyrrolidone to form a slurry. Then, this slurry is mixed with the positive electrode current collector 1.
The positive electrode 2 was produced by uniformly applying the solution to both sides of a 20 μm-thick aluminum foil having a thickness of 0, drying and compression molding with a roll press.

Next, a negative electrode 1 and a positive electrode 2 were sequentially laminated via a separator 3 made of a microporous polypropylene film having a thickness of 25 μm, and wound in a spiral shape many times to produce a wound body. . Then, the insulating plate 4 was inserted into the bottom of the nickel-plated iron battery can 5 to house the wound body. Then, in order to collect the current of the negative electrode, one end of a nickel negative electrode lead 11 was pressed against the negative electrode 1 and the other end was welded to the battery can 5. Further, in order to collect the current of the positive electrode, one end of an aluminum positive electrode lead 12 is attached to the positive electrode 2, and the other end is electrically connected to the battery lid 7 via a current interrupting thin plate 8 which interrupts current according to the internal pressure of the battery. Connected.

Next, propylene carbonate (PC) 2
9.95% by volume and dimethyl carbonate (DMC) 7
0% by volume and 3-methyl-2-oxazolidone (OZ)
LiP as an electrolyte in a mixed solvent with 0.05% by volume
A non-aqueous electrolyte in which 1 mol / l of F ₆ was dissolved was prepared.
Then, the non-aqueous electrolyte is injected into the battery can 5, and the battery can 5 is caulked through the insulating sealing gasket 6 coated with asphalt to fix the battery cover 7, and the diameter 18
A cylindrical nonaqueous electrolyte secondary battery having a height of 65 mm and a height of 65 mm was produced.

Examples 2 to 5 Propylene carbonate (PC) was used as the non-aqueous electrolyte.
And dimethyl carbonate (DMC) and 3-methyl-
2-oxazolidone (OZ) was mixed at the mixing ratio shown in Table 1, and a non-aqueous electrolytic solution of cylindrical type was used in the same manner as in Example 1 except that an electrolyte in which 1 mol / l of LiPF ₆ was dissolved was used as an electrolyte. A liquid secondary battery was manufactured.

Example 6 A negative electrode 1 was produced as follows.

As the negative electrode active material, graphite powder (KS-75, manufactured by Lonza Co., Ltd.) was used.
75) was mixed with 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture, which was further dispersed in N-methyl-2-pyrrolidone to form a slurry. . Then, this slurry is mixed with the negative electrode current collector 9.
Was coated uniformly on both sides of a 10 μm-thick strip-shaped copper foil, dried, and compression-molded with a roll press to produce a negative electrode 1. The graphite powder (KS-75) has a (002) plane spacing of 0.3358 nm and a C-axis crystallite thickness of 25.4 n.
m, a crystal structure having a G value of 8.82 in Raman spectrum, a true density of 2.23 g / cm ³ , and an average particle size of 28.4 μm.

The positive electrode 2 was produced in the same manner as in Example 1.

The non-aqueous electrolyte is ethylene carbonate (E
C) 29.95% by volume of dimethyl carbonate (DM
C) A solution prepared by dissolving 1 mol / l of LiPF ₆ as an electrolyte in a mixed solvent of 70% by volume and 0.05% by volume of 3-methyl-2-oxazolidone (OZ) was prepared.

Except for the above, a cylindrical non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.

Examples 7 to 10 Ethylene carbonate (EC) was used as a non-aqueous electrolyte.
Dimethyl carbonate (DMC) and 3-methyl-2-
Oxazolidone was mixed at a mixing ratio shown in Table 1 and a cylindrical nonaqueous electrolyte battery was produced in the same manner as in Example 6, except that a solution in which 1 mol / l of LiPF ₆ was dissolved was used as an electrolyte. .

Comparative Example 1 Propylene carbonate (PC) 3 was used as the non-aqueous electrolyte.
1 mol of LiPF ₆ as an electrolyte in a mixed solvent of 0 vol% and 70 vol% of dimethyl carbonate (DMC)
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that a solution prepared by dissolving / l was used.

Comparative Examples 2 to 6 Propylene carbonate (PC) was used as the non-aqueous electrolyte.
And dimethyl carbonate (DMC) and 3-methyl-
2-oxazolidone was mixed at the mixing ratio shown in Table 1 and a cylindrical non-aqueous electrolyte secondary solution was prepared in the same manner as in Example 1 except that a solution in which 1 mol / l of LiPF ₆ was dissolved was used as an electrolyte. A battery was manufactured.

Comparative Example 7 As a non-aqueous electrolyte, ethylene carbonate (EC) 30
% By volume and 70% by volume of dimethyl carbonate (DMC)
In a mixed solvent with LiPF ₆ 1 mol /
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 6, except that a solution prepared by dissolving 1 was used.

Comparative Examples 8 to 12 As a non-aqueous electrolyte, ethylene carbonate (EC) was used.
Dimethyl carbonate (DMC) and 3-methyl-2-
Oxazolidone (OZ) was mixed at the mixing ratio shown in Table 1, and a non-aqueous cylindrical electrolyte solution was prepared in the same manner as in Example 6 except that a solution in which 1 mol / l of LiPF ₆ was dissolved was used as an electrolyte. A secondary battery was manufactured.

Table 1 shows the mixing ratio of each solvent when preparing the non-aqueous electrolyte of the cylindrical non-aqueous electrolyte batteries of Examples 1 to 10 and Comparative Examples 1 to 12.

[0055]

[Table 1]

<Evaluation> The non-aqueous electrolyte secondary batteries produced in Examples 1 to 10 and Comparative Examples 1 to 12 were tested as follows, and the cycle characteristics, low temperature characteristics and load were measured. The properties were evaluated.

(1) Cycle Characteristics First, charging at a constant current of 1 A at 23 ° C. was performed at an upper limit voltage of 4.
The charging was performed up to 2 V, and thereafter, constant-voltage charging was performed until the charging time reached a total of 3 hours. Subsequently, discharge was performed at a constant current of 0.7 A to a final voltage of 2.75 V, which was defined as one cycle. Then, such charge / discharge was repeated 100 cycles, and the discharge capacity retention ratio (%) at the 100th cycle when the capacity at the second cycle was 100% (initial discharge capacity) was determined by the following equation (1).

[0058]

(Equation 1)

FIG. 2 shows the results of tests in Examples 1 to 5 and Comparative Examples 1 to 6 (using a propylene carbonate (PC) electrolyte). In FIG. 2, the result of the initial discharge capacity is 3-methyl-2-oxazolidone (O
The discharge capacity in the second cycle of Comparative Example 1 in which Z) was not mixed with the electrolytic solution was set to 100%.

Examples 6 to 10 and Comparative Example 7
FIG. 3 shows the results of tests in Comparative Example 12 (using an ethylene carbonate (EC) electrolyte). In FIG. 3, the result of the initial discharge capacity is 100% of the discharge capacity in the second cycle of Comparative Example 7 in which 3-methyl-2-oxazolidone (OZ) is not mixed with the electrolytic solution.

(2) Low-temperature characteristics Under three kinds of temperature conditions of -20 ° C., -10 ° C. and 0 ° C., constant current charging of 1 A is performed up to an upper limit voltage of 4.2 V, and thereafter, charging time is 3 hours in total. The battery was charged at a constant voltage until. Subsequently, the cut-off voltage is 2.75 at a constant current of 0.7 A.
Discharge was performed to V, and discharge capacity (%) at each temperature was determined.

FIG. 4 shows the results of tests in Examples 1 to 5 and Comparative Examples 1 to 6 (using a propylene carbonate (PC) electrolyte). In FIG. 4, 3-
The discharge capacity of Comparative Example 1 in which methyl-2-oxazolidone (OZ) was not mixed with the electrolytic solution was set to 100%.

Examples 6 to 10 and Comparative Example 7
FIG. 5 shows the results of tests in Comparative Example 12 (using an ethylene carbonate (EC) electrolyte). In FIG. 5, the discharge capacity of Comparative Example 7 in which 3-methyl-2-oxazolidone (OZ) was not mixed with the electrolytic solution was set to 100%.

(3) Load Characteristics First, a constant current charge of 1 A at 23 ° C. was performed with an upper limit voltage of 4.
The charging was performed up to 2 V, and thereafter, constant-voltage charging was performed until the charging time reached a total of 3 hours. Subsequently, 0.2A, 0.7
Discharge was performed to a final voltage of 2.75 V with three types of constant currents A and 2A, and the discharge capacity (%) at each current value was determined.

FIG. 6 shows the results of tests in Examples 1 to 5 and Comparative Examples 1 to 6 (using a propylene carbonate (PC) electrolyte). In FIG. 6, 3-
The discharge capacity of Comparative Example 1 in which methyl-2-oxazolidone (OZ) was not mixed with the electrolytic solution was set to 100%.

Examples 6 to 10 and Comparative Example 7
FIG. 7 shows the results of tests in Comparative Example 12 (using an ethylene carbonate (EC) electrolyte). In FIG. 7, the discharge capacity of Comparative Example 7 in which 3-methyl-2-oxazolidone (OZ) was not mixed with the electrolytic solution was set to 100%.

2 and 3, the non-aqueous electrolytic solutions of Examples 1 to 10 in which 3-methyl-2-oxazolidone is contained in the non-aqueous electrolytic solution in a range of 0.05 vol% or more and less than 1 vol%. The liquid secondary batteries are the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 12 in which 3-methyl-2-oxazolidone is contained in the non-aqueous electrolyte solution in a range of less than 0.05% by volume and 1% by volume or more. It can be seen that the initial discharge capacity is improved as compared with the battery. In addition, the nonaqueous electrolyte secondary batteries of Examples 1 to 10 all showed a high discharge capacity retention ratio of 90% or more in the discharge capacity retention ratio.
The discharge capacity retention rates of the non-aqueous electrolyte secondary batteries of No. 2 were all 90
%. Therefore, from this, 0.05% by volume of 3-methyl-2-oxazolidone is contained in the non-aqueous electrolyte.
It can be seen that the non-aqueous electrolyte secondary battery improves the initial discharge capacity and the discharge capacity retention rate by containing it in the range of less than 1% by volume.

4 and 5, the non-aqueous electrolytic solutions of Examples 1 to 10 in which 3-methyl-2-oxazolidone is contained in the non-aqueous electrolytic solution in a range of 0.05% by volume to less than 1% by volume. The liquid secondary batteries are the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 12 in which 3-methyl-2-oxazolidone is contained in the non-aqueous electrolyte solution in a range of less than 0.05% by volume and 1% by volume or more. It can be seen that the discharge capacity is improved at all temperatures of 0 ° C., −10 ° C., and −20 ° C. as compared with the battery. Therefore, by including 3-methyl-2-oxazolidone in the non-aqueous electrolyte in the range of 0.05% by volume or more and less than 1% by volume, the non-aqueous electrolyte secondary battery has a discharge capacity even at a low temperature. Is improved, that is, the low-temperature characteristics are improved.

6 and 7, the non-aqueous electrolytes of Examples 1 to 10 in which 3-methyl-2-oxazolidone is contained in the non-aqueous electrolyte in a range of 0.05 vol% or more and less than 1 vol%. The liquid secondary batteries are the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 12 in which 3-methyl-2-oxazolidone is contained in the non-aqueous electrolyte solution in a range of less than 0.05% by volume and 1% by volume or more. It can be seen that the discharge capacity is improved under all discharge conditions where the discharge current is 0.2 A, 0.7 A, and 2 A, as compared with the battery. Therefore, by including 3-methyl-2-oxazolidone in the non-aqueous electrolyte in the range of 0.05% by volume or more and less than 1% by volume, the non-aqueous electrolyte secondary battery can reduce the load during discharging. It can be seen that the discharge capacity is improved even when it is increased, that is, the load characteristics are improved.

[0070]

As described above, according to the present invention, a negative electrode made of a carbon material capable of doping and undoping lithium and a positive electrode made of a composite oxide of lithium and one or more transition metals are used. A non-aqueous electrolyte solution comprising an electrolyte dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte solution contains 3-methyl-2-oxazolidone in an amount of 0.05% by volume or more. By containing less than the volume%, a non-aqueous electrolyte battery having excellent initial characteristics, cycle characteristics, low-temperature characteristics, and load characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical nonaqueous electrolyte secondary battery to which the present invention is applied.

FIG. 2 is a characteristic diagram showing an initial discharge capacity and a discharge capacity retention ratio of Examples 1 to 5 and Comparative Examples 1 to 6.

FIG. 3 shows Examples 6 to 10 and Comparative Examples 7 to 1
2 is a characteristic diagram showing an initial discharge capacity and a discharge capacity retention ratio of No. 2; FIG.

FIG. 4 is a characteristic diagram showing low-temperature characteristics of Examples 1 to 5 and Comparative Examples 1 to 6.

FIG. 5 shows Examples 6 to 10 and Comparative Examples 7 to 1
FIG. 4 is a characteristic diagram illustrating low-temperature characteristics of the second example.

FIG. 6 is a characteristic diagram showing load characteristics of Examples 1 to 5 and Comparative Examples 1 to 6.

FIG. 7 shows Examples 6 to 10 and Comparative Examples 7 to 1;
FIG. 4 is a characteristic diagram illustrating a load characteristic of No. 2;

[Explanation of symbols]

1 negative electrode, 2 positive electrode, 3 separator, 4 insulating plate, 5
Battery can, 6 Insulation sealing gasket, 7 Battery lid, 8
Current interrupting thin plate, 9 negative electrode current collector, 10 positive electrode current collector,
11 negative electrode lead, 12 positive electrode lead

Claims (8)

[Claims] 1. An anode made of a carbon material capable of doping and undoping lithium, a cathode made of a composite oxide of lithium and one or more transition metals, and an electrolyte dissolved in a non-aqueous solvent. A non-aqueous electrolyte secondary battery comprising: a non-aqueous electrolyte, wherein the non-aqueous electrolyte is 3-methyl-2 represented by the following chemical formula 1.
-A non-aqueous electrolyte secondary battery containing oxazolidone in a range of 0.05 vol% or more and less than 1 vol%. Embedded image 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous solvent contains propylene carbonate. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous solvent contains propylene carbonate and a chain ester. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the chain ester is a compound selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous solvent contains ethylene carbonate. 6. The non-aqueous solvent according to claim 1, wherein the non-aqueous solvent contains ethylene carbonate and a chain ester.
The non-aqueous electrolyte secondary battery according to the above. 7. The non-aqueous electrolyte secondary battery according to claim 6, wherein the chain ester is a compound selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate. 8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode is a carbon material having a (002) plane spacing of 0.340 nm or less.