JP3089662B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery using a composite metal oxide containing Li for a positive electrode and a carbon material for a negative electrode. Next battery.

[Summary of the Invention]

The present invention provides a non-aqueous electrolyte secondary battery using a composite metal oxide containing Li as a positive electrode and a carbon material as a negative electrode, by using a mixed solvent of propylene carbonate and diethyl carbonate as an organic solvent for the electrolyte, An object of the present invention is to provide a non-aqueous electrolyte secondary battery that has an energy density, is pollution-free, and exhibits good charge / discharge cycle characteristics even at high temperatures.

[Prior art] With the emergence of new portable electronic devices such as camera-type VTRs, mobile phones, laptop computers, etc., one after another, which are becoming smaller and lighter, batteries for portable mobile power sources are becoming increasingly popular. Also, those having higher energy density are required.

Conventionally, aqueous batteries such as lead batteries and nickel cadmium batteries are generally used as secondary batteries, but these batteries exhibit excellent cycle characteristics, but are sufficiently satisfactory in terms of energy density and the like. However, there is a problem from the standpoint of environmental protection, and the development of a secondary battery that can replace these batteries is desired.

Under such circumstances, there is a great deal of interest in non-aqueous electrolyte secondary batteries (so-called lithium secondary batteries) that are non-polluting and have a high energy density due to a high operating voltage.

In nonaqueous electrolyte batteries, the energy density of the battery is determined by the characteristics of the anode, and a great number of cathode materials have been proposed and evaluated.

On the other hand, in the case of a secondary battery, the success or failure of development depends on how to develop a lithium anode having good cycle characteristics.

However, from this point of view, it must be said that the results of development of the lithium anode are extremely small.

For example, a lithium secondary battery using lithium metal for the negative electrode in the size of an AA battery has been announced and its excellent characteristics have been introduced, but some troublesome problems related to the lithium negative electrode have not been solved. is there.

That is, in a non-aqueous electrolyte secondary battery using lithium metal or lithium alloy for the negative electrode, lithium is inactivated and deposited in a powder form as charge / discharge cycles are repeated, and lithium is dendrite-shaped during charging. It grows and passes through the micropores of the separator membrane or the inter-fiber voids of the separator nonwoven fabric to reach the positive electrode, causing an internal short circuit, so that a sufficient charge / discharge cycle life cannot be obtained. Furthermore, since the activity of metallic lithium is very high,
There is still a problem in terms of safety.

Therefore, a so-called Li-CIC (carbon-lithium intercalation compound) electrode has been developed as a negative electrode material replacing the lithium negative electrode, and is considered to be highly promising in terms of cycle life and the like. That is, a so-called Li-Carbon Intercalation Compound in which lithium ions are intercalated into a certain kind of carbon material.
s) is capable of electrochemically performing a reversible oxidation-reduction reaction accompanied by undoping and doping of lithium ions in an organic electrolyte containing a lithium salt, and has an oxidation-reduction potential of about 0.02.
Since it is in the range of 1.0 to 1.0 V, it can be an excellent negative electrode material of a nonaqueous electrolyte secondary battery in combination with an appropriate positive electrode material. That is, in the battery system using the carbon-lithium intercalation compound as a negative electrode, in discharging, lithium ions doped in the negative electrode carbon migrate to the positive electrode and escort electrons coming from the negative electrode through an external circuit inside the positive electrode body. And in charging,
The lithium ions that have migrated to the positive electrode return to the negative electrode, and play a role of escorting the electrons returning through an external circuit inside the negative electrode body. Therefore, in any process of charging and discharging, since there is no metallic lithium inside the battery, the deposition of inert lithium and the growth of dendrites do not occur. Further, since the crystal structures of the positive electrode active material and the negative electrode active material are not easily broken, extremely good charge / discharge cycle characteristics can be obtained.

On the other hand, in a non-aqueous electrolyte secondary battery, the characteristics of an organic electrolyte to be used are very important for obtaining good charge / discharge characteristics. For this reason, many studies have been made on the relationship between the characteristics of the organic electrolyte and the charge / discharge characteristics, and the following findings have been obtained for the lithium anode nonaqueous electrolyte secondary battery.

1. The conductivity of the organic electrolyte is significantly improved by a combination of a high dielectric constant solvent and a low viscosity solvent. This can be explained semi-quantitatively by the dissociation of ions in the electrolyte and the mobility of the ions.

2. The higher the conductivity of the electrolyte, the smaller the polarization of the lithium negative electrode, and the higher the charge / discharge efficiency.

3. A system in which propylene carbonate, sulfolane, or dimethyl sulfoxide is used as a high dielectric constant solvent and 1,2-dimethoxyethane is mixed as a low viscosity solvent provides high conductivity and excellent lithium charge / discharge performance.

[Problems to be solved by the invention]

However, the present inventors have repeatedly studied and found that a non-aqueous electrolyte secondary battery using a carbon-lithium intercalation compound as a negative electrode, for example, an electrolytic solution using a mixed solvent of propylene carbonate and 1,2-dimethylethane as an organic solvent. When a liquid is used, the charge / discharge cycle is somewhat good at normal temperature, but when charge / discharge is repeated at a high temperature (for example, 40 ° C.), the capacity is rapidly reduced, and the cycle life is about 1 / compared to normal temperature. It turned out that the inconvenience of becoming 10 occurs.

As a matter of course, the performance required for a secondary battery that can replace the existing Ni-Cd battery and lead battery must be one that can operate sufficiently from low temperature (at least -20 ° C) to high temperature (at least 45 ° C). Must.

Therefore, a rapid decrease in capacity under a high-temperature environment in a nonaqueous electrolyte secondary battery using a carbon-lithium intercalation compound as a negative electrode greatly hinders practical application.

Accordingly, the present invention has been proposed in view of such a conventional situation, and has a high energy density, is non-polluting, and has a superior cycle life even in a high temperature environment. It is intended to provide a battery.

[Means for Solving the Invention] The present inventors have conducted various studies to improve the extreme decrease in cycle life at the time of high temperature use, and as a result, the inventors have found that the electrolyte is the most excellent as an electrolyte for a conventional lithium anode secondary battery. The mixed solvent of propylene carbonate and dimethoxyethane, which is said to be, is not always optimal in a non-aqueous electrolyte secondary battery using a carbon-lithium intercalation compound as a negative electrode, For non-aqueous electrolyte secondary batteries, an electrolyte using diethyl carbonate (diethyl carbonate) is the most suitable among various low-viscosity solvents, and can greatly improve the cycle life at high temperatures. I came to find.

That is, the non-aqueous electrolyte secondary battery of the present invention is Li _x MO
_{2 wherein} M represents at least one of Co, Ni and Mn, and x is 1 or 0.5;
A negative electrode containing a carbonaceous material as a negative electrode material having a (002) plane spacing d ₀₀₂ of 3.70 ° or more and having no exothermic peak at 700 ° C. or more in differential thermal analysis, and the organic solvent of the electrolytic solution is propylene carbonate. It is a mixed solvent of diethyl carbonate.

By assembling a battery using Li _x MO ₂ (for example, LiCoO ₂ ) as a positive electrode and a carbon material as a negative electrode and charging the battery, a secondary battery having a carbon-lithium intercalation compound as a negative electrode is obtained by the reaction of formula (1). The charge / discharge reaction of this secondary battery is as shown in equation (2).

The average discharge voltage of this secondary battery is very high at about 3.6V,
Therefore, a secondary battery of AA size and a high energy density of 180 Wh / 1 or more is realized. Recharging time can be sufficient even with relatively quick charging for one hour.

Furthermore, there is no reduction in the cycle life under light load discharge seen in lithium secondary batteries using metal lithium as the negative electrode. As for the cycle life, a long life of about 1200 cycles has been confirmed even at a discharge depth of 100% when used at normal temperature.

However, when the organic solvent of the electrolytic solution is a mixed solvent of propylene carbonate and 1,2-dimethoxyethane, a high temperature (4
When the charge / discharge cycle is repeated at 0 ° C), the capacity rapidly decreases, and at room temperature, the life of 1200 cycles becomes about 1/10.

Therefore, in the present invention, a decrease in the cycle life at the high temperature is improved by using a mixed solvent of propylene carbonate and diethyl carbonate as the organic solvent of the electrolytic solution.

In this case, the mixing ratio of propylene carbonate and diethyl carbonate is preferably in the range of propylene carbonate: diethyl carbonate = 75: 25 to 15:85, and particularly, propylene carbonate: diethyl carbonate = 60: 40 to 20:80. Within this range, good charge / discharge cycle characteristics can be obtained even under low temperature conditions.

As the electrolyte, LiPF ₆ is most suitable,
In addition, LiAsF ₆ , LiClO _{4 and the} like can be used.

On the other hand, for the positive electrode material, a composite metal oxide Li containing lithium is used.
_x MO ₂ is used, and as the composite metal oxide, Li
CoO ₂ , LiNi _y Co _1-y O ₂ (where 0 <y <1), LiNiO ₂ , Li
Mn ₂ O ₄ , and mixtures thereof, and the like are preferable.

As the carbon material for the negative electrode, the (002) plane spacing d
Any carbonaceous material having a ₀₀₂ of 3.70 ° or more and having no exothermic peak at 700 ° C. or more in differential thermal analysis can be used, and the carbon materials listed below are suitable.

First, a carbonaceous material obtained by carbonizing an organic material by a method such as firing.

As the organic material as a starting material, furfuryl alcohol or a furan resin made of a homopolymer or copolymer of furfural is preferable. Specific examples include polymers composed of furfural + phenol, furfuryl alcohol + dimethylolurea, furfuryl alcohol, furfuryl alcohol + formaldehyde, furfural + ketones, and the like. The carbonaceous material obtained by carbonizing this furan resin has a (002) plane spacing d ₀₀₂ of 3.70Å or more, and 700 ° C. in differential thermal analysis (DTA) in an air stream.
As described above, it does not have an exothermic peak and exhibits very good characteristics as a negative electrode material of a battery.

Alternatively, a petroleum pitch having an H / C atomic ratio of 0.6 to 0.8 is used as a raw material, a functional group containing oxygen is introduced into this, and a so-called oxygen cross-linking is performed to obtain a precursor having an oxygen content of 10 to 20% by weight. A carbonaceous material obtained by firing is also suitable. Such a carbonaceous material is also described, for example, in Japanese Patent Publication No. 53-31116, etc., but here, by optimizing the oxygen content, the plane distance d ₀₀₂ of the (002) plane is set to 3.70 ° or more, and the differential thermal analysis is performed. A carbonaceous material having no exothermic peak at 700 ° C. or higher in (DTA) and used as the negative electrode material.

Further, a carbonaceous material having a large doping amount with respect to lithium by adding a phosphorus compound or a boron compound when carbonizing the furan resin or petroleum pitch or the like can be used.

Examples of the phosphorus compound include phosphorus oxides such as phosphorus trioxide, phosphorus tetroxide and phosphorus pentoxide, and oxoacids such as orthophosphoric acid (so-called phosphoric acid), metaphosphoric acid and polyphosphoric acid.
Furthermore, salts of these oxo acids are mentioned, but phosphoric acid is preferred from the viewpoint of easy handling.

The amount of the phosphorus compound added during the carbonization of the organic material is 0.2 to 15% by weight in terms of phosphorus with respect to the organic material and the carbonaceous material, and the phosphorus content in the carbonaceous material is
The content is preferably set to 0.2 to 5.0% by weight.

Examples of the boron compound include oxides of boron such as diboron dioxide, diboron trioxide (so-called boron oxide), tetraboron trioxide, and tetraboron pentoxide, orthoboric acid (so-called boric acid), metaboric acid, tetraboric acid, And oxo acids of boron such as hypoboric acid and salts thereof. Any of these boron compounds can be added to a reaction system for carbonization in the form of an aqueous solution.

The amount of the boron compound added when carbonizing the organic material is 0.15 to 2.5% by weight in terms of boron with respect to the organic material and the carbonaceous material, and the content of boron in the carbonaceous material is 0.1 to 2.0%. It is preferable to set the weight%.

[Action]

In a non-aqueous electrolyte secondary battery using a composite metal oxide containing lithium as a positive electrode and a carbon material as a negative electrode, it has been considered to be optimal for a conventional lithium secondary battery using metal lithium as a negative electrode as an organic solvent for the electrolyte. When a mixed solvent of propylene carbonate and dimethoxyethane is used, the capacity significantly decreases when charge and discharge are repeated in a high-temperature environment.

On the other hand, when a mixed solvent of propylene carbonate and diethyl carbonate is used, a good cycle life is achieved even in a high-temperature environment.

〔Example〕

Embodiments to which the present invention is applied will be described based on specific experimental results.

Example 1 In this example, a non-graphite carbon material was used as a negative electrode material, a mixture of LiCoO ₂ and LiNi _0.6 Co _0.4 O ₂ was used as a positive electrode material, and propylene carbonate (PC) and diethyl carbonate (DEC) were used as organic solvents of an electrolyte. 2) is an example of a non-aqueous electrolyte secondary battery using the mixed solvent of (1).

To produce the negative electrode, first, a petroleum pitch is used as a starting material, and 10 to 20% of a functional group containing oxygen is introduced into the pitch (so-called oxygen crosslinking), and then fired at 1000 ° C. in an inert gas stream. A non-graphite carbon material was obtained. As a result of X-ray diffraction measurement of the non-graphite carbon material obtained at this time, the (002) plane spacing was 3.76 ° and the true specific gravity was 1.58.
Met.

This hard graphite carbon material was pulverized to obtain a carbon material powder having an average particle size of 10 μm. Then, 90 parts by weight of the carbon material powder was mixed with 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture, and the negative electrode mixture was dispersed in a solvent N-methyl-2-pyrrolidone to form a slurry. To prepare a negative electrode slurry.

Then, the obtained negative electrode slurry is uniformly applied to both sides of a 10 μm-thick strip-shaped copper foil serving as a negative electrode current collector, dried, and then compression-molded with a roll press to produce a strip-shaped negative electrode. did.

On the other hand, to prepare a positive electrode, lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol to 1 mol, and calcined in air at 900 ° C. for 5 hours to obtain LiCoO ₂ . Next, lithium carbonate, nickel carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol: 0.6 mol: 0.4 mol, respectively, and calcined in air at 900 ° C. for 5 hours to obtain LiNi _0.6 Co _0.4 O ₂ .

LiCoO ₂ 54.6 parts by weight thus obtained and LiNi _0.6 C
30.4 parts by weight of _0.4 O ₂ were 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.
Dispersed in methyl-2-pyrrolidone to form a slurry,
A positive electrode slurry was prepared.

Then, the positive electrode slurry is formed into a 20 μm thick positive electrode current collector.
Was uniformly coated on both sides of the aluminum foil strip and dried, and then compression-molded with a roll press to produce a belt-shaped positive electrode.

Next, as shown in FIG. 1, when a strip-shaped negative electrode (1), a strip-shaped positive electrode (2), and a separator (3) made of a microporous polypropylene film were each made into a spiral electrode element, the outer diameter was 20 mm and the height was 51 mm. The length and width were adjusted in advance so as to have a size that could be properly accommodated in the battery can (5), thereby producing a spiral electrode.

The spiral electrode manufactured in this manner was housed in a nickel-plated iron battery can (5), and insulating plates (4) were arranged on both upper and lower surfaces of the housed spiral electrode. And
From positive electrode current collector (10) to aluminum positive electrode lead (12)
And a nickel negative electrode lead (11) was drawn out from the negative electrode current collector (9) and welded to the battery can (5).

Then, LiPF ₆ is dissolved in a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate at a ratio of 1 mol / to prepare an electrolytic solution, and the electrolytic solution is poured into the battery can (5). The battery cover (7) is fixed by caulking the battery can (5) through an insulating sealing gasket (6) coated with asphalt, and a cylindrical non-aqueous electrolyte battery having a diameter of 20 mm and a height of 50 mm (implemented) Example Battery 1) was produced.

Example 2 This example is an example of a non-aqueous electrolyte secondary battery using LiCoO ₂ alone as a positive electrode material.

Cylindrical nonaqueous electrolytic secondary battery (Example battery 2) in the same manner as in Example 1 except that 91 parts by weight of LiCoO ₂ was mixed with 3 parts by weight of polyvinylidene fluoride and 6 parts by weight of graphite to prepare a positive electrode mixture. Was prepared.

Comparative Example 1 In this comparative example, a mixed solution of propylene carbonate and 1,2-dimethoxyethane was used as an organic solvent instead of the mixed solvent of propylene carbonate and diethyl carbonate of Example 1.

Cylindrical nonaqueous electrolytic secondary battery (Comparative Example 1 Battery 1) in the same manner as in Example 1 except that LiPF ₆ was dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane to prepare an electrolytic solution.
Was prepared.

The battery of Example 1, the battery of Example 2, and the battery of Comparative Example 1 produced as described above were repeatedly charged and discharged at a temperature of 45 ° C., and the discharge capacity in each cycle was obtained. The result is shown in FIG.

Note that charging was performed at a constant current of 1 A for 3 hours with a charging voltage set to a maximum of 4.1 V, and discharging was performed to a final voltage of 2.75 V with a constant resistance of 6.2 ohms.

As is clear from FIG. 2, propylene carbonate and 1,2-
Comparative battery 1 using a mixed solvent with dimethoxyethane
Has a large decrease in discharge capacity due to repeated charging and discharging,
At the 100th cycle, the initial discharge capacity of 980 mAh is 560 mAh (57
%). On the other hand, in the battery 1 of the embodiment, at the 100th cycle, the initial 950 mAh is merely reduced to 800 mAh (84%). Also in the battery 2 of the embodiment, the initial 980 mAh at the 100th cycle is merely reduced to 830 mAh.

As described above, in the comparative example battery 1 using the mixed solvent of propylene carbonate and dimethoxyethane, the capacity greatly decreased at 45 ° C., whereas the electrolytic solution according to the present invention (the mixed solvent of propylene carbonate and diethyl carbonate) In Example Battery 1 and Example Battery 2 each using, even at 45 ° C., the capacity was only slightly reduced as compared with room temperature, and it can be seen that the effect was large.

However, in the same discharge cycle test at normal temperature, the degree of the capacity decrease accompanying the cycle was not changed in any of the comparative example battery 1, the example battery 1 and the example battery 2, and at the time of 100 cycles, both of the initial capacity decreased. 90%.

Example 3 In this example, a nonaqueous electrolyte secondary battery using pitch coke as a negative electrode material, LiMn ₂ O ₄ as a positive electrode material, and a mixed solvent of propylene carbonate and diethyl carbonate as an organic solvent for the electrolyte was used. This is an example.

To produce the negative electrode, first, pitch coke was pulverized to an average particle size of 40 μm, and then fired at 1000 ° C. in an inert gas stream to obtain a carbon material powder.

90 parts by weight of this carbon material powder was mixed with 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture,
This mixture was dispersed in a solvent n-methyl-2-pyrrolidone to form a slurry, thereby preparing a negative electrode slurry.

Then, the negative electrode slurry is applied to a thickness of 10 to serve as a negative electrode current collector.
After uniformly applying and drying both sides of a strip-shaped copper foil having a thickness of μm, the strip-shaped copper foil was compression-molded with a roll press to produce a strip-shaped negative electrode.

On the other hand, to produce a positive electrode, first, manganese dioxide and lithium carbonate heat-treated at 400 ° C. were mixed at a ratio of 1 mol to 0.25 mol, and calcined in air at 850 ° C. for 5 hours to produce LiMn ₂ O
₄ (Li _0.5 MnO ₂ ) was obtained.

Then, 86 parts by weight of the LiMn ₂ O ₄ were mixed with 10 parts by weight of graphite as a conductive agent and 4 parts by weight of polyvinylidene fluoride as a binder to prepare a positive electrode mixture. The slurry was dispersed in 2-pyrrolidone to prepare a positive electrode slurry.

Lastly, the positive electrode slurry is converted to a positive electrode current collector having a thickness of 30%.
After being uniformly applied to both sides of the μm band-shaped aluminum foil and dried, the band-shaped positive electrode was prepared by compression molding with a roll press.

Next, when the separator composed of the strip-shaped negative electrode, the strip-shaped positive electrode, and the microporous polypropylene film having a thickness of 25 μm is formed into a spiral electrode element, the width and length of each are set so that the dimensions can be appropriately accommodated in the battery can. After adjustment, a spiral electrode was manufactured. The spiral electrode manufactured in this manner was housed in a nickel-plated iron battery can, and insulating plates were arranged on both upper and lower surfaces of the spiral electrode. Then, an aluminum positive electrode lead was derived from the positive electrode current collector, and a nickel negative electrode lead was derived from the negative electrode current collector and welded to the battery can, respectively.

Then, an electrolyte is prepared by dissolving LiPF _{6 in} a mixed solvent of 25% by volume of propylene carbonate and 25% by volume of diethyl carbonate at a ratio of 1 mol / mol, and this electrolyte is poured into a battery tube to remove asphalt. The battery lid is fixed by caulking the battery can through the applied insulating sealing gasket, 14 mm in diameter,
A 50 mm high cylindrical nonaqueous electrolyte battery (Example Battery 3) was produced.

Comparative Example 2 In this comparative example, a mixed solvent of propylene polycarbonate and 1,2 dimethoxyethane was used as an organic solvent instead of the mixed solvent of propylene carbonate and diethyl carbonate of Example 3.

Propylene carbonate 50% by volume and 1,2-dimethoxyethane 50
A cylindrical non-aqueous electrolyte secondary battery (Comparative Battery 2) was produced in the same manner as in Example 3, except that LiPF ₆ was dissolved in a mixed solvent with a volume percentage of LiPF ₆ to prepare an electrolytic solution.

The battery of Example 3 and the battery of Comparative Example 2 produced as described above were repeatedly charged and discharged in an atmosphere at 45 ° C., respectively, and the discharge capacity in each cycle was measured. The result is shown in FIG.

For charging, set the charging voltage to a maximum of 4.2 V and set the charging voltage to 400 mA.
The discharge was performed at a constant current of 3 hours at a constant current of 200 mA to a final voltage of 2.75 V.

As is clear from FIG. 2, propylene carbonate and 1,2-
Comparative battery 2 using a mixed solvent with dimethoxyethane
In the case of, the capacity decrease accompanying the cycle is large. At the 100th cycle, the initial 405 mAh drops to 200 mAh (49%).
On the other hand, in Example Battery 3 using the mixed solvent of propylene carbonate and diethyl carbonate, the discharge capacity at the 100th cycle was 82% of the initial discharge capacity, and the discharge capacity was slightly reduced. Recognize.

Therefore, even in a non-aqueous electrolyte secondary battery using pitch coke as a negative electrode material and LiMn ₂ O ₄ as a positive electrode material, it is preferable to use a mixed solvent of propylene carbonate and diethyl carbonate as an organic solvent for the electrolyte. It was shown that charge-discharge cycle characteristics were achieved.

The charge / discharge cycle characteristics were also examined at room temperature in the same manner. As a result, the batteries of Comparative Example 2 and Example 3 had a discharge capacity at the time of 100 cycles of about 88% of the initial discharge capacity.

Comparative Example 3 In this comparative example, metallic lithium was used as the negative electrode material, LiCoO ₂ was used as the positive electrode material, and a mixed solvent of propylene carbonate and diethyl carbonate was used as the organic solvent of the electrolytic solution.

In order to produce a negative electrode, first, 80 μm of metallic lithium was used as a negative electrode current collector and bonded to both sides of a 15 μm-thick strip-shaped copper foil with a roll press to produce a strip-shaped negative electrode.

On the other hand, to prepare a positive electrode, LiCoO ₂ was mixed with graphite as a conductive agent and polyvinylidene fluoride as a binder according to the following composition to prepare a positive electrode mixture, and this positive electrode mixture was N-methyl-2- The slurry was dispersed in pyrrolidone to prepare a positive electrode slurry.

Then, the positive electrode slurry was 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 with a roll press to produce a strip-shaped positive electrode.

Next, the width and length of each separator are adjusted so that the separator composed of the strip-shaped lithium metal negative electrode, the strip-shaped positive electrode, and the microporous polypropylene film has a dimension that can be appropriately accommodated in the battery can when the spiral electrode element is used. A formula electrode was prepared. The spiral electrode manufactured as described above was housed in a nickel-plated iron battery can, and insulating plates were arranged on the upper and lower surfaces of the spiral electrode. Then, an aluminum positive electrode lead was derived from the positive electrode current collector, and a nickel negative electrode lead was derived from the negative electrode current collector and welded to the battery can, respectively.

Next, Li in a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate in the battery can.
An electrolyte in which PF ₆ was dissolved at a rate of 1 mol / injection was injected, and the battery lid was fixed by caulking the battery can through an insulating sealing gasket coated with asphalt.
A cylindrical nonaqueous electrolyte battery (comparative battery 3) having a height of 50 mm was produced.

The battery of Comparative Example 3 was repeatedly charged and discharged at room temperature, and the discharge capacity at each cycle was measured. The result is shown in FIG.

For charging, set the charging voltage to a maximum of 4.1 V and set it to 250 mA
The current was applied for 7 hours, and the discharge was started at a voltage of 2.
It went to 75V.

As shown in FIG. 4, the discharge capacity is greatly reduced as charge and discharge are repeated, and is reduced to 56% of the initial discharge capacity in 50 cycles. Therefore, these results show that in a nonaqueous electrolytic secondary battery having a lithium electrode as a negative electrode, the charge / discharge cycle characteristics are not improved even when a mixed solvent of propylene carbonate and diethyl carbonate is used as an organic solvent. It has been found that the mixed solvent exhibits the effect of improving the charge / discharge cycle characteristics only when used in a nonaqueous electrolytic battery using a carbon material for the negative electrode.

〔The invention's effect〕

As is clear from the above description, the nonaqueous electrolyte secondary battery of the present invention is a nonaqueous electrolyte secondary battery in which a composite metal oxide containing Li is used as a positive electrode and a carbon material is used as a negative electrode. Since a mixed solvent of propylene carbonate and diethyl carbonate is used as the organic solvent, it has a high energy density, is non-polluting, and has a good charge / discharge cycle life even in a high temperature environment.

Therefore, according to the non-aqueous electrolyte secondary battery of the present invention,
Even small portable devices, which have been developed in recent years, can supply a sufficient amount of energy with a long cycle life without impairing their small size and light weight. Further, since the nonaqueous electrolyte secondary battery has good charge / discharge cycle characteristics even at high temperatures, it can be used in a wide range of fields as a secondary battery replacing a lead battery or a nickel cadmium battery. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration example of a cylindrical non-aqueous electrolyte secondary battery. FIGS. 2 to 4 are characteristic diagrams showing the difference in the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery depending on the type of the organic solvent of the electrolyte. DESCRIPTION OF SYMBOLS 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 5 ... Battery can 7 ... Battery cover

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toru Nagaura 1-1 Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture 1-1 Sony Energy Tech Koriyama Plant (56) References JP-A-4-171675 ( JP, A) JP-A-4-171674 (JP, A) JP-A-4-155775 (JP, A) JP-A-3-252065 (JP, A) JP-A-2-172163 (JP, A) JP JP-A-2-172162 (JP, A) JP-A-2-139861 (JP, A) JP-A-2-66856 (JP, A) JP-A-2-12777 (JP, A) JP-A-2-10666 (JP) JP-A-63-299056 (JP, A) JP-A-63-121260 (JP, A) JP-A-63-121259 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H01M 10/40 H01M 4/02 H01M 4/58

Claims (3)

(57) [Claims] 1. A distance between a positive electrode containing Li _x MO ₂ (where M represents at least one of Co, Ni, and Mn, and x is 1 or 0.5) as a positive electrode material, and a (002) plane. d ₀₀₂ is a negative electrode containing a carbonaceous material having no exothermic peak at 700 ° C. or higher as an anode material in and differential thermal analysis at least 3.70A, organic solvent of the electrolytic solution is a mixed solvent of propylene carbonate and diethyl carbonate Non-aqueous electrolyte secondary battery characterized by the above-mentioned. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the mixing ratio of the propylene carbonate and diethyl carbonate is 75:25 to 15:85 by volume. 3. The positive electrode and the negative electrode are strip-shaped electrodes obtained by molding the positive electrode material or the negative electrode material on both sides of a current collector, and the positive electrode and the negative electrode are wound through a separator to form a spiral electrode. The non-aqueous electrolyte secondary battery according to claim 1, wherein: