JPH05234619A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To improve cycle life characteristics under heavy loading conditions, of nonaqueous electrolyte secondary battery in which special lithium compound is used as an active material for positive electrode and electrode materials capable of doping and undoping lithium is used for negative electrode. CONSTITUTION:A nonaqueous electrolyte secondary battery is composed of a positive electrode which contains LixMO2 (M represents more than one kind of transition metal and 0.05<=x<=1.10) as a positive electrode active material a negative, electrode which can dope and undope lithium, and nonaqueous electrolyte. A solvent consisting of three kinds of material, that is, propylene carbonate, ethylene carbonate, and diethyl carbonate is used as a solvent of the electrolyte.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery having improved cycle characteristics by using a mixed solvent of propylene carbonate, ethylene carbonate and diethyl carbonate as a solvent for the non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras and radio-cassettes, there is an increasing demand for rechargeable secondary batteries in place of disposable primary batteries.

By the way, most of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte. However, since the voltage of this battery is about 1.2V, it is difficult to improve the energy density of the battery. There is also a drawback that the self-discharge rate at room temperature is as high as 20% or more in one month.

Therefore, as a secondary battery having a voltage of 3 V or higher and a high energy density and a low self-discharge rate, a nonaqueous solvent is used as an electrolyte and a light metal such as metallic lithium is used as a negative electrode. Non-aqueous electrolyte secondary batteries have been investigated. However, such a non-aqueous electrolyte secondary battery has a drawback that metallic lithium or the like used for the negative electrode grows in a dendrite shape by repeated charging and discharging and contacts the positive electrode, and as a result, a short circuit easily occurs inside the battery. Have. Therefore, practical application is difficult.

Therefore, a non-aqueous electrolytic solution in which lithium or the like is alloyed with another metal and this alloy is used for the negative electrode has been studied. However, since such an alloy is likely to be granulated when charging and discharging are repeated, it is still difficult to put it into practical use.

On the other hand, a non-aqueous electrolyte secondary battery using a carbonaceous material, such as coke, which can be doped or dedoped with lithium, as a negative electrode active material (JP-A-62-90863).
No. Gazette) was proposed. This non-aqueous electrolyte secondary battery,
Since the negative electrode does not have the above-mentioned drawbacks, the cycle life characteristics are improved to some extent.

On the other hand, Li _x MO ₂ (where M represents one or more kinds of transition metals, and 0.05 ≦ x ≦ 1.10) is used as the positive electrode active material of the non-aqueous electrolyte secondary battery. , Which has been proposed as an active material capable of improving battery capacity and obtaining high energy density (Japanese Patent Application No. 63-135099).

Further, as an electrolytic solution for a non-aqueous electrolytic solution secondary battery using a carbon-lithium intercalation compound, a solution obtained by dissolving an electrolyte such as LiPF ₆ in an organic solvent is used. A mixed solvent system of propylene and diethyl carbonate is said to be preferable because it can improve the cycle characteristics under a high temperature environment (Japanese Patent Application No. 2-312481).
issue).

[0009]

However, Li _x MO ₂ (where M represents one or more kinds of transition metals, and 0.05 ≦ x ≦ 1.10) is used as the positive electrode active material,
Doping lithium with the negative electrode, using an electrode material that can be dedoped, and even using a mixed solvent system of propylene carbonate and diethyl carbonate as the solvent of the electrolytic solution described above, under high voltage heavy load discharge conditions There is a problem that the cycle characteristics cannot be improved sufficiently.

The present invention is intended to solve the problems of the prior art, and Li _{x is} used as a positive electrode active material.
MO ₂ (wherein M represents one or more kinds of transition metals, 0.0
5 ≦ x ≦ 1.10) and improve the cycle life characteristics under heavy load condition in a non-aqueous electrolyte secondary battery using an electrode material capable of doping and dedoping lithium in the negative electrode. It is an object.

[0011]

The inventor of the present invention has conducted various studies in order to achieve the above-mentioned object, and as a result, in a non-aqueous electrolyte secondary battery using a carbon-lithium intercalation compound, electrolysis was performed. It was previously said that it was optimal as a liquid,
The LiPF ₆ that was dissolved in a mixed solvent system of propylene carbonate and diethyl carbonate, using the _Li x MO ₂ in the positive electrode,
It is not always optimal for a battery using a carbonaceous material for the negative electrode, and as a solvent for the electrolyte of such a battery, a three-component system in which ethylene carbonate having a higher dielectric constant is added to propylene carbonate and diethyl carbonate is used. The inventors have found that the solvent is optimal and can improve the cycle life characteristics under heavy load conditions, and completed the present invention.

That is, according to the present invention, as the positive electrode active material, Li _x MO ₂ (wherein M represents one or more transition metals,
0.05 ≦ x ≦ 1.10), a negative electrode that can be doped with lithium and dedoped, and a non-aqueous electrolyte secondary battery, the non-aqueous electrolysis solution comprising: Provided is a non-aqueous electrolyte secondary battery characterized in that a solvent of the liquid is a mixed solvent of three kinds of propylene carbonate, ethylene carbonate and diethyl carbonate.

As described above, the non-aqueous electrolyte secondary battery of the present invention uses, as a solvent of the non-aqueous electrolyte, a mixed solvent of three kinds in which ethylene carbonate having a high dielectric constant is added in addition to propylene carbonate and diethyl carbonate. It is characterized by In this case, the mixing ratio of the solvent is preferably 3 to 60% by volume of ethylene carbonate. In this case, the blending amounts of propylene carbonate and diethyl carbonate are not particularly limited, but propylene carbonate is preferably 10 to 60% by volume and diethyl carbonate is 10 to 10% by volume.
It is 60% by volume, and more preferably the volume mixing ratio of propylene carbonate, ethylene carbonate and diethyl carbonate is 3: 3: 4.
Alternatively, it is 2.5: 2.5: 5 or 1: 1: 1.

Generally, N-is used as a solvent having a high dielectric constant.
Organic solvents such as methylformamide and formamide, and water can be used, but they cannot be used as a solvent for a nonaqueous electrolytic solution because they react with lithium.

As long as the non-aqueous electrolyte secondary battery of the present invention uses a mixed solvent of propylene carbonate, ethylene carbonate and diethyl carbonate as a solvent for the non-aqueous electrolyte as described above, other configurations are Li _x MO ₂ as a positive electrode active material
Can be used in the same manner as a conventional non-aqueous electrolyte secondary battery using an electrode material capable of doping and dedoping lithium in the negative electrode.

That is, as the electrolyte of the non-aqueous electrolyte, for example, lithium perchlorate, lithium borofluoride, lithium phosphorofluoride, lithium chloroaluminate, lithium halide, lithium trifluoromethanesulfonate and the like can be used.

The positive electrode is made of Li _x MO as a positive electrode active material.
₂ (However, M represents one or more kinds of transition metals, and 0.05 ≦
x ≦ 1.10) is used, and in this case, the transition metal constituting the positive electrode active material is preferably at least one of Co and Ni.

The negative electrode is composed of an electrode material which can be doped and dedoped with lithium. As such an electrode material, a carbonaceous material can be used, and more specifically, pyrolytic carbons and coke. It is possible to use materials (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired bodies (phenol resin, furan resin, etc. fired), carbon fibers, activated carbon, etc. it can.

The shape of the battery is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape can be used.

[0020]

In the non-aqueous electrolyte secondary battery of the present invention, Li _x MO ₂ (where M represents one or more transition metals, and 0.05 ≦ x ≦ 1.10) is used as the positive electrode active material. Lithium is used for the negative electrode, and an electrode material that can be dedoped is used, and as a solvent for the electrolyte, propylene carbonate,
Since the three-type mixed solvent in which ethylene carbonate and diethyl carbonate, which is a high dielectric constant solvent, are mixed is used, the energy density is high, and the cycle characteristics under the heavy load discharge conditions of high voltage are sufficiently improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings.

Example 1 As shown in FIG. 1, a cylindrical non-aqueous electrolyte secondary battery in which a strip-shaped positive electrode 1 and a strip-shaped negative electrode 2 were wound around a separator 3 and accommodated in a battery can 5 was prepared as follows. Manufactured to.

In producing the strip-shaped negative electrode 2, first, petroleum pitch is used as a starting material, and 10 to 20% of a functional group containing oxygen is introduced into this (so-called oxygen cross-linking), and then at 1000 ° C. in an inert gas stream. It was fired to obtain a non-graphite material. In addition, as a result of X-ray diffraction measurement of the obtained difficult-to-graphite material,
The spacing between (002) planes is 3.76 angstroms,
The true specific gravity was 1.58. Crush this difficult graphite material,
A carbon material powder having an average particle size of 10 μm was used. Then, 90 parts by weight of this carbon material powder is mixed with 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in N-methyl-2-pyrrolidone to form a slurry. A negative electrode slurry was prepared.

The negative electrode slurry thus obtained was
A strip-shaped negative electrode 2 was prepared by uniformly coating both sides of a strip-shaped copper foil having a thickness of 10 μm as a negative electrode current collector, drying it, and compression-molding it with a roller press.

On the other hand, in producing the strip-shaped positive electrode 1, first, lithium carbonate and cobalt carbonate are added in a molar ratio of 0.5.
The mixture was mixed at a ratio of 1 mol and calcined in air at 900 ° C. for 5 hours to obtain LiCoO ₂ . And the obtained LiCoO
₂ 91 parts by weight, 6 parts by weight of graphite as a conductive agent, a mixture of 3 parts by weight of polyvinylidene fluoride positive electrode mixture was prepared as a binder, the positive electrode mixture N- methyl-2-
A positive electrode slurry was prepared by dispersing in pyrrolidone to form a slurry.

The positive electrode slurry thus obtained is
A strip-shaped positive electrode 1 was prepared by uniformly coating the both sides of a strip-shaped aluminum foil having a thickness of 20 μm as a positive electrode current collector, drying it, and compression-molding it with a roller press.

Then, as shown in FIG. 1, the strip-shaped positive electrode 1, the strip-shaped negative electrode 2, and the separator 3 made of a microporous polypropylene film were spirally wound to form a spiral electrode 4. In this case, the spiral electrode 4 has an outer diameter of 13.8.
mm, the height is 51.8 mm, and the strip-shaped positive electrode 1, the strip-shaped negative electrode 2, and the separator 3 are preliminarily set so as to be properly housed in the battery can 5.
I adjusted the length and width.

The spiral electrode 4 thus produced is
It was housed in a battery case 5 made of iron plated with nickel, and insulating plates 6 were arranged on both upper and lower surfaces of the spiral electrode 4. Then, the aluminum positive electrode lead 7 was led out from the positive electrode current collector 1a and welded to the battery lid 8, and the nickel negative electrode lead 9 was led out from the negative electrode current collector 2a and welded to the battery can 5.

The electrolytic solution was prepared by dissolving LiPF _{6 in a} mixed solvent of propylene carbonate 48.5% by volume, diethyl carbonate 48.5% by volume and ethylene carbonate 3% by volume at a ratio of 1 mol / liter. Then, the electrolytic solution is injected into the battery can 5, and the battery lid 8 is fixed by caulking the upper part of the battery can 5 through the insulating sealing gasket 10 coated with asphalt, and the diameter is 13.8 mm and the height is 5.
A 1.8 mm cylindrical non-aqueous electrolyte secondary battery was prepared.

Examples 2 to 10 and Comparative Examples 1 to 2 The composition of the electrolytic solution was changed as shown in Tables 1 and 2, and Example 1 was changed.
A non-aqueous electrolyte secondary battery was manufactured in the same manner as.

Evaluation In order to evaluate the cycle characteristics of the batteries of Examples 1 to 10 and Comparative Examples 1 and 2 produced as described above, charging and discharging were repeated at a temperature of 23 ° C. and 10
Cycle discharge capacity, 100 cycle discharge capacity,
The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 10th cycle (capacity retention rate%) was determined. The results are shown in Tables 1 and 2. The charging voltage is 4.1V.
Set to 1 A constant current for 2 hours and discharge 600
The final voltage was 2.75 V at a constant current of mA.

Further, the batteries of Examples 6 to 10 were subjected to a discharge test at a low temperature (-10 ° C) to determine the discharge capacity (mAh). In this case as well, charging was performed at a charging voltage of 4.1 V and a constant current of 1 A for 2 hours, and discharging was performed at a constant current of 600 mA up to a cutoff voltage of 2.75 V. The obtained discharge capacity (mAh) is shown in Table 1.

Further, regarding the cycle characteristics, Example 1
~ 5 and the results of Comparative Examples 1-2, the relationship between the volume ratio and the capacity retention ratio of ethylene carbonate in the solvent is plotted in Fig. 2,
From the results of Examples 6 to 10, the relationship between the ratio of propylene carbonate to the total of propylene carbonate and diethyl carbonate and the capacity retention ratio was plotted in FIG. Also, low temperature (-10 ℃)
From the results of the discharge test in Fig. 4, the relationship between the ratio of diethyl carbonate to the total of propylene carbonate and diethyl carbonate and the discharge capacity was plotted in Fig. 4.

From these results, regarding the cycle characteristics, the volume ratio of ethylene carbonate is preferably 3 to 60%, and the mixing ratio of propylene carbonate and diethyl carbonate is 20:80 to.
It was found to be effective at 90:10. Further, in order to secure sufficient discharge characteristics at low temperature, it is preferable that the volume ratio of ethylene carbonate is 3 to 50% and the mixing ratio of propylene carbonate and diethyl carbonate is 20:80 to 60:40. all right.

[0035]

[Table 1] Example No. 1 2 3 4 5 Electrolyte solvent (volume%) Propylene carbonate 48.5 40 35 30 20 Diethyl carbonate 48.5 40 35 30 20 Ethylene carbonate 3 20 30 40 60 Cycle characteristics (capacity Wh / l) 10th cycle 146 140 153 155 141 100th cycle 104 102 113 115 98 Capacity retention ratio (%) 71.2 72.7 74.4 74.2 69.7 Low temperature discharge capacity (mAh) − − − − − Example No. 6 7 8 9 10 Electrolyte solvent (volume%) Propylene carbonate 60 40 30 20 10 Diethyl carbonate 10 30 40 50 60 Ethylene carbonate 30 30 30 30 30 Cycle characteristics (capacity Wh / l) 10th cycle 151 152 150 147 142 100th cycle 109 112 111 105 97 Capacity retention (%) 72.9 73.8 74.0 71.4 68.5 Low temperature discharge capacity (mAh) 116 143 153 163 168

[0036]

[Table 2] Comparative example No. Comparative Example 1 Comparative Example 2 Solvent of electrolyte (volume%) Propylene carbonate 50 0 Diethyl carbonate 50 0 Ethylene carbonate 0 100 Cycle characteristics (capacity Wh / l) 10th cycle 144 140 100th cycle 100 92 Capacity retention (%) 69.4 65.8 Low temperature discharge capacity (mAh) − −

[0037]

According to the present invention, L is used as the positive electrode active material.
i _x MO ₂ (where M represents one or more transition metals,
0.05 ≦ x ≦ 1.10), and the cycle life characteristics under heavy load conditions are improved in a non-aqueous electrolyte secondary battery using an electrode material capable of doping and dedoping lithium in the negative electrode. It becomes possible.

[Brief description of drawings]

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

FIG. 2 is a graph showing the relationship between the volume ratio of ethylene carbonate and the capacity retention ratio.

FIG. 3 is a graph showing the relationship between the capacity retention and the ratio of propylene carbonate to the total of propylene carbonate and diethyl carbonate.

FIG. 4 is a graph showing the relationship between the ratio of diethylyl carbonate to the total of propylene carbonate and diethyl carbonate and the discharge capacity.

[Explanation of symbols]

 1 strip positive electrode 2 strip negative electrode 3 separator 4 spiral electrode 5 battery can

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masanori Anzai, Masanori Anzai 1-1, Shimosugishita, Takakura, Hiwata-cho, Koriyama-shi, Fukushima Prefecture Sony Energy Tech Co., Ltd. Koriyama Plant (72) Yasunobu Koga, Kuniyama-shi, Fukushima Prefecture 1-1 Shimo-Sugishita Takakura, Wada-machi Sony Energy Tech Koriyama Factory

Claims (1)

[Claims] 1. A positive electrode active material comprising Li _x MO ₂ (provided that
M represents one or more kinds of transition metals, and 0.05 ≦ x ≦ 1.1
A positive electrode containing 0), and doped with lithium,
In a non-aqueous electrolyte secondary battery comprising a dedoped anode and a non-aqueous electrolyte, the solvent of the non-aqueous electrolyte is composed of a mixed solvent of three kinds of propylene carbonate, ethylene carbonate and diethyl carbonate. And a non-aqueous electrolyte secondary battery.