JPH09199172A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the cycle characteristic under the high-voltage, heavy-load discharge condition by using at least one kind of diester oxalate for a nonaqueous solvent in a nonaqueous electrolytic solution secondary battery. SOLUTION: This nonaqueous electrolytic solution secondary battery is provided with a positive electrode 2 containing a lithium-containing composite oxide, a negative electrode 1 containing a carbon material capable of doping and undoping lithium ions, and a nonaqueous electrolytic solution dissolved with a lithium salt electrolyte in a nonaqueous solvent. At least one kind of diester oxalate is used for the nonaqueous solvent. The cycle characteristic under the high-voltage, heavy-load discharge condition can be improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode containing a lithium-containing composite oxide, a negative electrode containing a carbon material capable of doping and dedoping lithium ions, and a lithium salt electrolyte dissolved in a non-aqueous solvent. Non-aqueous electrolyte secondary battery comprising the following non-aqueous electrolyte. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery having excellent cycle characteristics under high voltage and heavy load discharge conditions.

[0002]

2. Description of the Related Art In recent years, due to advances in electronic technology, high performance, miniaturization, and portability of electronic devices have advanced, and the demand for high energy density batteries used in these portable electronic devices has increased. Conventionally, nickel-cadmium batteries and lead batteries have been used as secondary batteries used in these electronic devices.
In reality, the requirements for a battery having a low V), a large battery weight and a large battery volume, and a high energy density have not been met.

Recently, as a battery system satisfying these requirements, a non-aqueous electrolyte secondary battery having a negative electrode made of metallic lithium or a lithium alloy has attracted attention and has been actively studied. However, in the case of non-aqueous electrolyte secondary batteries that use metallic lithium as the negative electrode, the cycle life and rapid charging characteristics are practically sufficient due to the dissolution of metallic lithium, the generation of dendrites at the time of cracking, and the miniaturization of precipitated lithium. There is a problem that it does not exhibit various characteristics.

[0004] In order to solve these problems,
Research and development of a lithium-ion non-aqueous electrolyte secondary battery in which a material capable of doping and de-doping with lithium ions, for example, a carbon material as a negative electrode is active. Non-aqueous electrolyte secondary battery using such a negative electrode, since lithium does not exist in the metal state, there is no problem related to deterioration of cycle characteristics and rapid charge characteristics due to the metal lithium negative electrode,
It exhibits excellent battery characteristics. Further, as compared with the nickel-cadmium battery, the low self-discharge property required for the secondary battery is also improved, and there is an advantage that there is no memory effect. Furthermore, by using a lithium-containing composite oxide having a high redox potential for the positive electrode, the voltage of the battery (about 4.2 V) is increased, so that a battery having a high energy density can be realized.

By the way, as the non-aqueous electrolyte used in such a lithium ion non-aqueous electrolyte secondary battery,
A solution in which an electrolyte such as LiPF ₆ is dissolved in a non-aqueous solvent such as cyclic carbonic acid esters or chain carbonic acid esters is used. Above all, it is generally recommended to use a mixed solvent of propylene carbonate and diethyl carbonate as the non-aqueous solvent. When such a mixed solvent is used as a non-aqueous solvent, the lithium-ion non-aqueous electrolyte secondary battery is stored or used under high temperature conditions (for example, in a car in summer or in a warehouse in a hot and humid atmosphere). However, deterioration of cycle characteristics can be suppressed.

[0006]

However, when a mixed organic solvent of propylene carbonate and diethyl carbonate is used as a non-aqueous solvent for a non-aqueous electrolyte secondary battery, cycle characteristics under high-voltage and heavy-load discharge conditions. Was not sufficient, and further improvement was required.

The present invention is intended to solve the problems of the above-mentioned conventional techniques, and includes a positive electrode containing a lithium-containing composite oxide, a negative electrode containing a carbon material capable of doping and dedoping lithium ions, and lithium. It is an object of the present invention to improve the cycle characteristics under a high voltage and heavy load discharge condition of a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte solution obtained by dissolving a salt electrolyte in a non-aqueous solvent.

[0008]

The present inventor has found that the above object can be achieved by using an oxalic acid diester as a non-aqueous solvent of an electrolytic solution, and has completed the present invention.

That is, the present invention provides a positive electrode containing a lithium-containing composite oxide, a negative electrode containing a carbon material capable of doping and dedoping lithium ions, and a non-aqueous electrolysis obtained by dissolving a lithium salt electrolyte in a non-aqueous solvent. A non-aqueous electrolyte secondary battery including a liquid, wherein the non-aqueous solvent contains at least one kind of oxalic acid diester.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte secondary battery of the present invention
The non-aqueous solvent contains at least one oxalic acid diester. As a result, the cycle characteristics of the non-aqueous electrolyte secondary battery under high voltage and heavy load discharge conditions can be improved.

Although the reason why such an effect is obtained is not clear, it is considered as follows.

That is, since oxalic acid diesters are dibasic acid esters unlike ordinary fatty acid esters, they have higher reactivity with metal ions than conventional non-aqueous solvents such as propylene carbonate and diethyl carbonate. It is considered that the film is decomposed at the positive electrode, thereby forming a stable film on the surface of the positive electrode that does not hinder the electrode reaction but can prevent the decomposition of impurities and solvent molecules.

Preferred examples of the oxalic acid diester used in the present invention include dimethyl oxalate, diethyl oxalate, dipropyl oxalate, diisopropyl oxalate, methylethyl oxalate, methylpropyl oxalate and ethylpropyl oxalate. it can. Among them,
Diethyl oxalate is preferred from the viewpoint of ease of operation.

These oxalic acid diesters can be used as a mixture of two or more kinds.

In the present invention, 100% of the non-aqueous solvent may be composed of such an oxalic acid diester,
It can be used as a mixture with other non-aqueous solvent, if necessary. In that case, if the content of the oxalic acid diester in the non-aqueous solvent is too small, the cycle characteristics cannot be expected to be improved.
It is.

As the non-aqueous solvent which can be used in combination with the oxalic acid diesters, non-aqueous solvents conventionally used in lithium ion non-aqueous electrolyte secondary batteries, for example, propylene carbonate which is a high dielectric constant solvent, Examples thereof include ethylene carbonate, butylene carbonate, γ-butyrolactone and the like, and low viscosity solvents such as 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate.

Particularly, it is preferable to use at least one cyclic carbonate selected from the group consisting of propylene carbonate, ethylene carbonate and butylene carbonate.

When the non-aqueous solvent is composed of a two-component mixed system of oxalic acid diester and cyclic carbonic acid ester, the content of the oxalic acid diester in the non-aqueous solvent is preferably 1 to
It is 95% by volume, more preferably 20 to 80% by volume.
On the other hand, the content of the cyclic carbonic acid ester in the non-aqueous solvent at this time is preferably 5 to 99% by volume.

In the present invention, it is preferable from the viewpoint of cycle characteristics that the non-aqueous solvent is composed of a three-component mixed system by adding diethyl carbonate in addition to the two components of oxalic acid diester and cyclic carbonic acid ester.

When the non-aqueous solvent is composed of a three-component mixed system of oxalic acid diester, cyclic carbonic acid ester and diethyl carbonate, the content of oxalic acid diester in the non-aqueous solvent is
Preferably 1-90% by volume, more preferably 20-80
% By volume. On the other hand, the content of the cyclic carbonic acid ester in the non-aqueous solvent at this time is preferably 5 to 50% by volume, more preferably 10 to 40% by volume, and the content of diethyl carbonate in the non-aqueous solvent is preferably Is 5 to 50% by volume, and more preferably 10 to 45% by volume.

The electrolyte used in preparing the non-aqueous electrolyte by dissolving it in the above non-aqueous solvent is generally
LiClO ₄ , LiA used for lithium batteries
sF ₆ , LiPF ₆ , LiBF ₄ , LiCl, LiBr,
CH ₃ SO ₃ Li, may be mentioned CF ₃ SO ₃ Li and the like. These can be used alone or in combination of two or more.

As the positive electrode of the lithium ion non-aqueous electrolyte secondary battery of the present invention, a positive electrode active material using a lithium-containing composite oxide is used. As a result, a secondary battery with high energy density can be constructed.

Here, as the lithium-containing composite oxide, those conventionally used as a positive electrode active material of a lithium ion secondary battery can be used, and in particular, the formula (1)

[0024]

Embedded image Li _x MO ₂ (1) (where M is a transition metal, preferably Co, Ni and Mn
X is 0.05 ≦ x ≦ 1.10
Is a number that satisfies. )) Can be preferably used. In the equation, the value of x changes within the range of 0.05 ≦ x ≦ 1.10. Here, when the transition metal M is Mn, Li _x Mn ₂ O ₄ , L
Any of the i _x MnO ₂ can be used.

When forming a positive electrode from such a lithium-containing composite oxide, a known conductive material, binder or the like can be added.

Such a lithium-containing composite oxide is, for example, a salt of each of lithium and transition metal M, for example,
Carbonates, nitrates, sulfates, oxides, hydroxides, halides and the like can be used as raw materials for production. For example, the lithium salt raw material and the transition metal M salt raw material may be weighed according to a desired composition, sufficiently mixed, and then heated and baked in a temperature range of 600 ° C. to 1000 ° C. in an oxygen-existing atmosphere. . In this case, the mixing method of each component is not particularly limited, and powdery salts may be mixed as they are in a dry state, or powdery salts may be dissolved in water and mixed in an aqueous solution. You may.

As the negative electrode constituting the non-aqueous electrolyte secondary battery of the present invention, a carbon material capable of doping and dedoping lithium ions is used, but such a carbon material is relatively low at 2000 ° C. or lower. A low crystalline carbon material obtained by firing at a temperature or a raw material that easily crystallizes is 3000 ° C.
It is possible to use a highly crystalline carbon material or the like that has been treated at a high temperature nearby. For example, pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), artificial graphites, natural graphites, glassy carbons, organic polymer compound fired bodies (fired furan resin, etc. at an appropriate temperature) Carbonized), carbon fiber, activated carbon and the like can be used. Among them, a low crystalline carbon material having a (002) plane spacing of 3.70 angstroms or more, a true density of less than 1.70 g / cc, and having no exothermic peak at 700 ° C. or more in a differential thermal analysis in an air stream, A highly crystalline carbon material having a high negative electrode mixture filling property and a true specific gravity of 2.10 g / cc or more can be preferably used.

When forming the negative electrode from such a material, a known binder or the like can be added.

Other configurations of the separator, battery can, PTC element, current collector and the like of the non-aqueous electrolyte secondary battery of the present invention may be the same as those of the conventional lithium ion non-aqueous electrolyte secondary battery. it can. In addition, the procedure for assembling the battery can be performed in the same manner as the conventional one.

The shape of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape may be used as necessary. can do.

As described above, in the non-aqueous electrolyte secondary battery of the present invention, by using the specific oxalic acid diester as the non-aqueous solvent, the cycle characteristics under high voltage and heavy load discharge conditions are improved. Therefore, it is suitable as a power source for various small electronic devices of recent years that require heavy load discharge.

[0032]

EXAMPLES Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described in detail with reference to examples.

Examples 1 to 21 and Comparative Examples 1 to 2 Specific description will be made with reference to the sectional views of the batteries shown in FIG.

(Preparation of Negative Electrode (1)) After introducing 10 to 20% of a functional group containing oxygen into petroleum pitch (oxygen cross-linking), it is fired at 1000 ° C. in an inert gas to approximate a glassy carbon material. A non-graphitizable carbon material having a property {interval of (002) plane = 3.76 angstrom (by X-ray diffraction measurement); true specific gravity = 1.58} was obtained.

Next, the obtained carbon material is treated with an average particle diameter of 10 μm.
m of powder. 90 parts by weight of this powder and 10 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to prepare a negative electrode mixture slurry.

Then, this slurry was added to the negative electrode current collector (1
0) was coated on both sides of a 10 μm-thick copper foil, dried, and then compression-molded with a roll press to produce a strip-shaped negative electrode (1).

(Production of Positive Electrode (2)) First, lithium carbonate and cobalt carbonate were mixed in a ratio of 0.5 mol to 1.0 mol, and calcined in air at 900 ° C. for 5 hours. Then, LiCoO ₂ was obtained.

Next, LiCoO ₂ was used as the positive electrode active material.
91 parts by weight and 6 parts by weight of graphite as a conductive material,
A positive electrode mixture was prepared by mixing 3 parts by weight of polyvinylidene fluoride as a binder, and the mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode mixture slurry.

Next, this slurry was added to the positive electrode current collector (11).
Was uniformly applied to both surfaces of a 20 μm-thick aluminum foil, dried, and compression-molded by a roll press to obtain a belt-shaped positive electrode (2).

(Production of Non-Aqueous Electrolyte Secondary Battery) The strip-shaped negative electrode (1) and positive electrode (2) produced as described above and having a thickness of 2
A separator (3) made of a microporous polyethylene film of 5 μm is laminated in order and wound around a center pin in large numbers, so that a nickel-plated iron battery can (5) (outer diameter 13.8 mm, A spiral electrode body having a size suitable to fit within a height of 51.8 mm) was produced.

Next, the spirally wound electrode body is housed in a battery can (5), insulating plates (4) are arranged on the upper and lower surfaces of the spirally wound electrode body, and the positive electrode (2) and the negative electrode (1) are respectively placed. Positive electrode lead (1
3) was led out from the positive electrode current collector (11) and connected to the battery lid (7) via a safety valve device (8) provided with a PTC element (9) as a current interrupting device. Further, a negative electrode lead (12) made of nickel was led out of the negative electrode current collector (10) and was welded to the battery can (5).

Next, into the battery can (5), a non-aqueous electrolytic solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / liter in the mixed non-aqueous solvent shown in Tables 1 to 3 was injected. Then, the battery lid (7) and the battery can (5) are caulked via the gasket (6) coated with asphalt to thereby remove the battery lid (7).
Was fixed. As a result, as shown in FIG.
A cylindrical non-aqueous electrolyte secondary battery having a height of 8 mm and a height of 50 mm was produced.

[0043]

[Table 1] (Volume%) Example Non-aqueous solvent 1 2 3 4 5 6 7 8 Dimethyl oxalate 1 10 30 50 70 80 90 95 Propylene carbonate 99 90 70 50 30 20 10 5

[0044]

[Table 2] (Volume%) Example Non-aqueous solvent 9 10 11 12 13 14 15 Diethyl oxalate 50 − − − − − − Dipropyl oxalate − 50 − − − − Diisopropyl oxalate − − 50 − − − − Methyl ethyl oxalate − − − 50 − − − Methyl propyl oxalate − − − − 50 − − Ethyl propyl oxalate − − − − − 50 50 Propylene carbonate 50 50 50 50 50 50 − Ethylene carbonate − − − − − − 50

[0045]

[Table 3] (Volume%) Examples Comparative Examples Non-aqueous solvent 16 17 18 19 20 21 12 Diethyl oxalate 1 10 40 60 80 90 − − Propylene carbonate 45 45 30 20 10 5 50 − Ethylene carbonate − − − − − − − 50 Diethyl carbonate 44 45 30 20 10 5 50 50

(Evaluation of Battery Performance) The following cycle life tests were conducted on the cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 21 and Comparative Examples 1 and 2 thus produced.

At a temperature of 23 ° C., a charging voltage of 4.20
V, the charging current is 1000 mA, charging is performed under the condition of charging time 2.5 h, and then the discharging current is 250 mA and the final voltage is 2.
The cycle of discharging under the condition of 75 V is repeated, the discharge capacity (Wh / l) at the 10th cycle and the 100th cycle is measured, and the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 10th cycle is expressed as the capacity retention ratio ( %). Table 4 shows the obtained results.

[0048]

[Table 4]

From the results shown in Table 4, the non-aqueous electrolyte secondary batteries of Examples 1 to 21 in which oxalic acid diesters were used as the non-aqueous solvent were the conventional cyclic carbonic acid ester and diethyl carbonate mixed as the non-aqueous solvent. It can be seen that the capacity retention rate was improved as compared with the batteries of Comparative Examples 1 and 2 using the solvent.

From the results of Examples 1 to 7, when a binary non-aqueous solvent containing a binary oxalate diester represented by diethyl oxalate and propylene carbonate was used,
It can be seen that the preferable range of the content of the oxalic acid diester in the non-aqueous solvent is at least 1 to 95% by volume.
Further, from the results of Examples 16 to 21, when a mixed non-aqueous solvent of a three-component system of oxalic acid diester typified by diethyl oxalate, propylene carbonate and diethyl carbonate was used, non-aqueous oxalic acid diester was used. It can be seen that the preferable range of the content in the solvent is at least 1 to 90% by volume.

[0051]

According to the present invention, a positive electrode containing a lithium-containing composite oxide, a negative electrode containing a carbon material capable of doping and dedoping lithium ions, and a non-aqueous solvent obtained by dissolving a lithium salt electrolyte in a non-aqueous solvent. It is possible to improve cycle characteristics of a non-aqueous electrolyte secondary battery including a water electrolyte under high voltage and heavy load discharge conditions.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

1 negative electrode, 2 positive electrode, 3 separator, 4 insulating plate, 5 battery can, 6 gasket, 7 battery cover,
8 safety valve device, 9 PTC element, 10 negative electrode current collector, 11 positive electrode current collector, 12 negative electrode lead, 13
Positive lead

Claims (10)

[Claims] 1. A positive electrode containing a lithium-containing composite oxide,
In a non-aqueous electrolyte secondary battery comprising a negative electrode containing a carbon material capable of doping and de-doping lithium ions, and a non-aqueous electrolyte solution obtained by dissolving a lithium salt electrolyte in a non-aqueous solvent,
A non-aqueous electrolyte secondary battery, wherein the non-aqueous solvent contains at least one oxalic acid diester. 2. The oxalic acid diester is at least one selected from the group consisting of dimethyl oxalate, diethyl oxalate, dipropyl oxalate, diisopropyl oxalate, methylethyl oxalate, methylpropyl oxalate and ethylpropyl oxalate. The non-aqueous electrolyte secondary battery according to claim 1. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the oxalic acid diester is contained in the non-aqueous solvent in an amount of at least 1% by volume. 4. The non-aqueous solvent further contains at least one cyclic carbonate selected from the group consisting of propylene carbonate, ethylene carbonate and butylene carbonate.
3. The non-aqueous electrolyte secondary battery according to any one of 3. 5. An oxalic acid diester in a non-aqueous solvent is 1 to
The non-aqueous electrolyte secondary battery according to claim 4, which contains 95% by volume. 6. The cyclic carbonic acid ester is contained in a non-aqueous solvent in an amount of 5-9.
The non-aqueous electrolyte secondary battery according to claim 5, wherein the non-aqueous electrolyte secondary battery contains 9% by volume. 7. The non-aqueous electrolyte secondary battery according to claim 4, wherein the non-aqueous solvent further contains diethyl carbonate. 8. An oxalic acid diester in a non-aqueous solvent is 1 to
The non-aqueous electrolyte secondary battery according to claim 7, wherein the non-aqueous electrolyte secondary battery contains 90% by volume. 9. A cyclic carbonic acid ester is added to a non-aqueous solvent in an amount of 5-5.
The non-aqueous electrolyte secondary battery according to claim 8, wherein the non-aqueous electrolyte secondary battery contains 0% by volume and diethyl carbonate is contained in the non-aqueous solvent in an amount of 5 to 50% by volume. 10. The lithium-containing composite oxide has the formula (1): Li _x MO ₂ (1) (wherein, M is at least one kind of transition metal, and x is 0.05 ≦ x ≦ 1). 10 is a number satisfying 10.) The non-aqueous electrolyte secondary battery according to any one of claims 1 to 9.