JPH0896851A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE: To provide a nonaqueous electrolytic secondary battery capable of giving high energy density, displaying a good cycle characteristic even under a high voltage and heavy load discharge condition, and being compatible as a power source for electronic equipment consuming a large amount of current. CONSTITUTION: This nonaqueous electrolytic secondary battery is formed out of a positive electrode 2 made of a lithium transition metal matrix composite oxide expressed by Lix MO2 where M stands for one or more types of transition metals, a negative electrode 1 capable of doping and de-doping lithium, and a nonaqueous electrolytic solution with an electrolyte dissolved in a nonaqueous solvent. A mixed solvent of ethylene sulfite and a diester carbonate compound is used as the nonaqueous solvent.

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, and more particularly to improvement of a non-aqueous solvent.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras and radio cassettes, there is an increasing demand for secondary batteries that can be repeatedly charged and discharged, instead of disposable primary batteries.

Most of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte.
However, this battery has a low voltage of about 1.2 V, and it is difficult to improve the energy density. In addition, the self-discharge rate at room temperature is as high as about 20% per month, which is also a drawback.

Therefore, a non-aqueous solvent is used as the solvent for the electrolytic solution.
A lithium secondary battery using a light metal such as lithium for the negative electrode has been proposed. This lithium secondary battery has a high voltage of 3 V or more and can obtain a high energy density. Moreover, it has an advantage that the self-discharge rate is low.

However, in this lithium secondary battery, metallic lithium or the like used for the negative electrode grows into a dendrite-like crystal upon repeated charging and discharging, and reaches the positive electrode.
Practical application is difficult due to the drawback that internal short circuits are likely to occur.

In addition, a non-aqueous electrolyte secondary battery in which lithium or the like is alloyed with another metal and this alloy is used for a negative electrode has also been studied. However, in this case, there is a drawback that the alloy of the negative electrode is likely to be formed into particles by repeating charging and discharging, which is also difficult to put into practical use.

Therefore, as disclosed in, for example, Japanese Patent Application Laid-Open No. 62-90863, a lithium ion secondary battery (non-aqueous electrolyte secondary battery) using a carbonaceous material such as coke as a negative electrode active material is proposed. Proposed. This secondary battery utilizes doping / dedoping of lithium between carbon layers in a battery reaction, and does not show dendrite-like crystal growth of lithium or atomization in the negative electrode and is excellent in cycle life characteristics.

In particular, as a positive electrode active material, Li _x M
When a combination of lithium transition metal composite oxides represented by O ₂ (where M represents one kind or more than one kind of transition metal and x is 0.05 <x <1.10) is used, Battery capacity is improved and high energy density can be obtained.

[0009]

By the way, a non-aqueous electrolyte secondary battery (Li _x M) using a carbonaceous material as a negative electrode active material and a lithium transition metal composite oxide as a positive electrode active material in this way is described.
As a non-aqueous solvent for (O ₂ / C battery), a mixed solvent system of propylene carbonate and diethyl carbonate is said to be optimal from the viewpoint of improving cycle characteristics in a high temperature environment.

However, this mixed solvent system of propylene carbonate and diethyl carbonate is not necessarily optimal in terms of improving the cycle characteristics of the battery under high voltage and heavy load discharge conditions.

Therefore, the present invention has been proposed in view of such conventional circumstances, and provides a non-aqueous electrolyte secondary battery exhibiting excellent cycle characteristics even under high voltage and heavy load discharge conditions. The purpose is to

[0012]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies, and as a result, Li _x MO
_As a non-aqueous solvent for ₂ / C batteries, a mixed solvent of ethylene sulfite and a carbonic acid diester compound is most suitable. By using this mixed solvent, a high voltage and We have found that the improvement of cycle characteristics is achieved under the heavy load discharge condition.

The present invention has been completed based on such findings, and Li _x MO ₂ (where M represents one or more kinds of transition metals, and x is 0.05 ≦ x ≦ 1. 10), a positive electrode comprising a lithium-transition metal composite oxide represented by the formula (10), and a negative electrode capable of doping and dedoping lithium.
In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte solution obtained by dissolving an electrolyte in a non-aqueous solvent, the non-aqueous solvent is a mixed solvent of ethylene sulfite and a carbonic acid diester compound, Is.

Further, the carbonic acid diester is characterized by being either diethyl carbonate or methyl ethyl carbonate.

Further, the mixing ratio of ethylene sulfite in the non-aqueous electrolyte is 20 to 80% by volume.

The present invention provides a positive electrode composed of a lithium-transition metal composite oxide represented by Li _x MO ₂ (where M represents one or more kinds of transition metals), and a negative electrode capable of being doped and dedoped with lithium. And a non-aqueous electrolytic solution obtained by dissolving an electrolyte in a non-aqueous solvent.

In the present invention, a mixed solvent of ethylene sulfite and a carbonic acid diester compound is used as a non-aqueous solvent for such a non-aqueous electrolyte secondary battery. Ethylene sulphite is represented by the chemical formula 1, and when a mixed solvent of ethylene sulphite and a carbonic acid diester compound is used, the cycle characteristics under high voltage and heavy load discharge conditions are improved, and electronic devices with large current consumption are used. It can be used as a power supply.

[0018]

[Chemical 1]

The mixing ratio of ethylene sulfite in the above mixed solvent is preferably 20 to 80% by volume. If the mixing ratio of ethylene sulfite is below this range, the cycle characteristics cannot be sufficiently improved.

The carbonic acid diester compound is not particularly limited, and examples thereof include diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate and the like. These carbonic acid diester compounds may be used alone or in combination of two or more.

The non-aqueous electrolyte is formed by dissolving the electrolyte in the above non-aqueous solvent. As the electrolyte, for example, L
iClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ ,
LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃
Li or the like is used alone or in combination of two or more.

Further, in the non-aqueous electrolyte secondary battery of the present invention,
The negative and positive electrodes are made of the following materials.

First, for the negative electrode, a carbonaceous material used for doping and dedoping with lithium is used. For example, pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), graphites, glassy carbons, organic polymer compound fired bodies (furan resin, etc. are fired at an appropriate temperature to carbonize them. Materials), carbon fiber, activated carbon, etc. can be used. In particular, a carbonaceous material having a (002) plane spacing of 3.70 angstroms and a true density of less than 1.70 g / cc and having no exothermic peak at 700 ° C. or higher in a differential thermal analysis in an air stream is preferable. is there.

On the other hand, the positive electrode has Li _x MO ₂ (however, M
Represents one or more kinds of transition metals, and x is 0.05 ≦ x ≦
A lithium transition metal composite oxide represented by 1.10) is used. Of these, M is Co or Ni,
That is, LiCoO ₂ , LiNiO ₂ , LiNi _y Co
_1-y O _{2 and the} like are preferable.

[0025]

A positive electrode made of a lithium-transition metal composite oxide represented by Li _x MO ₂ (wherein M represents one or more kinds of transition metals and x is 0.05 ≦ x ≦ 1.10.), In a non-aqueous electrolyte secondary battery comprising a negative electrode capable of doping and de-doping lithium, and a non-aqueous electrolyte solution obtained by dissolving an electrolyte in a non-aqueous solvent, ethylene sulfite and a carbonic acid diester compound as a non-aqueous solvent The use of the mixed solvent improves the cycle characteristics under high voltage and heavy load discharge conditions.

[0026]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

Example 1 The non-aqueous electrolyte secondary battery prepared in this example is shown in FIG.
In this example, a non-aqueous electrolyte secondary battery having such a structure was manufactured as follows.

First, the negative electrode 1 was manufactured as follows.

Petroleum pitch was used as a starting material, 10 to 20% of a functional group containing oxygen was introduced into this (so-called oxygen cross-linking), and then fired in an inert gas stream at a temperature of 1000 ° C. A carbon material was obtained. The obtained non-graphitizable carbon material was subjected to X-ray diffraction measurement. As a result, the (002) plane spacing was 3.76 angstroms and the true specific gravity was 1.58 g / cc.

Next, the non-graphitizable carbon material was pulverized into a carbon material powder having an average particle size of 10 μm, and 90 parts by weight of this was mixed with 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode. A mixture was prepared. Then, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode slurry.

The negative electrode slurry thus prepared was
A strip-shaped negative electrode 1 was prepared by uniformly coating both sides of a strip-shaped copper foil having a thickness of 10 μm, which is a negative electrode current collector, and then drying and compression-molding it with a roll press.

On the other hand, the positive electrode 2 was manufactured as follows.

Lithium carbonate and cobalt carbonate were mixed in a ratio of 0.5 mol to 1.0 mol, and this mixture was calcined in air at a temperature of 900 ° C. for 5 hours to produce LiCoO ₂ .

91 parts by weight of this LiCoO ₂ was mixed with 6 parts by weight of graphite as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder to prepare a positive electrode mixture, and this positive electrode mixture was mixed with N-methyl- Dispersed in 2-pyrrolidone,
The positive electrode slurry was used.

Then, this positive electrode slurry is uniformly applied to both sides of a 20 μm-thick strip-shaped aluminum foil serving as a positive electrode current collector, dried, and then compression-molded by a roller press machine to prepare a strip-shaped positive electrode 2. did.

Then, the strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 thus produced were laminated with the separator 3 made of a microporous polypropylene film interposed therebetween, and were wound many times to produce a spiral electrode element. The dimensions of the negative electrode 1, the positive electrode 2 and the separator 3 were adjusted in advance so that the completed spirally wound electrode element could be properly accommodated in the battery can 5 having an outer diameter of 13.8 mm and a height of 51.8 mm.

The spiral electrode element thus produced was housed in a nickel-plated iron battery can 5, and insulating plates 4 were arranged on both upper and lower surfaces of the spiral electrode element. Then, from the positive electrode current collector 10 to the aluminum positive electrode lead 1
2, the nickel negative electrode lead 11 was led out from the negative electrode collector 9 and welded to the battery can 5.

Next, an electrolytic solution prepared by dissolving LiPF ₆ at a rate of 1 mol / l in a mixed solvent obtained by mixing 50% by volume of ethylene sulfite and 50% by volume of diethyl carbonate was injected into the battery can 5. .

Then, the battery lid 5 is fixed by caulking the battery can 5 through the insulating sealing gasket 6 coated with asphalt, and the cylindrical non-aqueous electrolyte solution 2 having an outer diameter of 13.8 mm and a height of 51.8 mm is fixed. A secondary battery was produced.

Example 2 A non-aqueous electrolyte secondary electrolyte was prepared in the same manner as in Example 1 except that a mixed solvent of 50% by volume of ethylene sulfite and 50% by volume of methyl ethyl carbonate was used as the non-aqueous solvent of the electrolytic solution. A battery was made.

Comparative Example 1 A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate was used as the non-aqueous solvent of the electrolytic solution. It was made.

Each battery manufactured as described above was subjected to constant current charging for 2 hours at a temperature of 23 ° C. under a charging voltage of 4.2 V and a charging current of 1 A, and then a discharge current of 700 m.
The charging / discharging cycle of repeating constant current discharge to a final voltage of 2.75 V under the condition A was repeated. And 10
The discharge capacity at the cycle and the discharge capacity at the 100th cycle were measured, and the capacity retention rate [(discharge capacity at the 100th cycle)]
/ (10th cycle discharge capacity) × 100] was determined.
The results are shown in Table 1.

[0043]

[Table 1]

As can be seen from Table 1, the battery of Example 1 using a mixed solvent of ethylene sulfite and diethyl carbonate as the non-aqueous solvent and the battery of Example 2 using a mixed solvent of ethylene sulfite and methyl ethyl carbonate. Has a larger capacity retention than the battery of Comparative Example 1 using a mixed solvent of propylene carbonate and diethyl carbonate.

From this, the mixed solvent of ethylene sulfite and the carbonic acid diester compound is more suitable as the non-aqueous solvent of the Li _x MO ₂ / C battery than the mixed solvent of propylene carbonate and diethyl carbonate. It was found that the cycle characteristics of the battery are improved by using.

Examination of Mixing Ratio of Non-Aqueous Solvent Examples except that an ethylene sulfite-diethyl carbonate mixed solvent or an ethylene sulfite-methyl ethyl carbonate mixed solvent having a mixing ratio shown in Tables 2 and 3 was used as the non-aqueous solvent. Non-aqueous electrolyte secondary battery (Experimental Example 1)
-Experimental example 12) was produced. Then, similarly to the above, the discharge capacity at the 10th cycle, the discharge capacity at the 100th cycle, and the capacity retention rate were obtained. The results are shown in Table 4 and Table 5.
Shown in.

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

[Table 5]

As can be seen from Tables 4 and 5, the ethylene sulfite-diethyl carbonate mixed solvent was used, and the ethylene sulfite-methyl ethyl carbonate mixed solvent was used. When the amount is in the range of 20 to 80% by volume, a large capacity retention rate can be obtained. However, when the amount of ethylene sulfite was less than this range as in Experimental Examples 6 and 12, the amount was 75
Only a capacity retention rate of less than% can be obtained.

From the above, it was found that it is suitable to set the mixing ratio of ethylene sulfite to 20 to 80% in the mixed solvent of ethylene sulfite and carbonic acid diester compound.

[0053]

As is apparent from the above description, the non-aqueous electrolyte secondary battery of the present invention is represented by Li _x MO ₂ (where M represents one or more kinds of transition metals). A positive electrode made of a lithium-transition metal composite oxide, a negative electrode capable of being doped and dedoped with lithium, and a non-aqueous electrolytic solution obtained by dissolving an electrolyte in a non-aqueous solvent, wherein the non-aqueous solvent is ethylene sal Since it is a mixed solvent of phyto and a carbonic acid diester compound, it is possible to obtain high energy density and also to obtain good cycle characteristics under high voltage and heavy load discharge conditions.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing a non-aqueous electrolyte secondary battery to which the present invention is applied.

[Explanation of symbols]

 1 negative electrode 2 positive electrode

Claims (3)

[Claims] 1. Li _x MO ₂ (wherein M represents one or more kinds of transition metals and x is 0.05 ≦ x ≦ 1.10.)
Non-aqueous electrolyte secondary comprising a positive electrode composed of a lithium-transition metal composite oxide represented by, a negative electrode capable of doping and de-doping lithium, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent A non-aqueous electrolyte secondary battery, wherein the non-aqueous solvent is a mixed solvent of ethylene sulfite and a carbonic acid diester compound. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbonic acid diester is either diethyl carbonate or methyl ethyl carbonate. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the mixing ratio of ethylene sulfite in the non-aqueous electrolyte is 20 to 80% by volume.