JP2001332296A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery, having superior and stable discharge characteristic and being superior in a charge/discharge cycle characteristic and a conservation characteristic under a charging condition. SOLUTION: The nonaqueous electrolyte secondary battery, provided with a positive pole, negative pole and nonaqueous electrolyte, specifies that the solvent of the nonaqueous electrolyte contains at least one of a nitrosco compound and nitron compound excluding nitrosobenzene.

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.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery.

[0003] As a secondary battery satisfying such requirements,
Secondary batteries using non-aqueous electrolytes have been put to practical use. This battery has several times the energy density of a battery using a conventional aqueous electrolyte.

For example, a lithium transition metal composite oxide such as a lithium cobalt composite oxide, a lithium nickel composite oxide or a lithium manganese composite oxide is used as a positive electrode active material of a nonaqueous electrolyte secondary battery, and a lithium metal is used as a negative electrode. And an active material such as a lithium alloy such as a Li-Al alloy capable of occluding and releasing lithium, or carbon as a host material using lithium ions (here, a host material refers to a material capable of occluding and releasing lithium ions). Lithium intercalation compound occluded in LiCl
A non-aqueous electrolyte secondary battery using an aprotic organic solvent in which a lithium salt such as O ₄ or LiPF ₆ is dissolved as an electrolytic solution is exemplified.

However, when these aprotic organic solvents are used as the electrolytic solution, there is a problem that the organic solvents deteriorate with time. For example, when the battery has a high voltage of 4.2 V or more, the organic solvent is decomposed and generates heat to increase the battery temperature, or the gas generated by the decomposition of the organic solvent causes the battery to swell. .

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 9-326262, nitrosobenzene, nitrobenzene, 2,2-diphenyl-
It contained a compound selected from 1-picrylhydrazyl. As a result, a non-aqueous electrolyte secondary battery which is stable even when used at a charging potential of 4 V or more and has excellent charge-discharge cycle characteristics and storage characteristics in a charged state has been obtained.

[0007]

However, when a compound selected from nitrosobenzene, nitrobenzene and 2,2-diphenyl-1-picrylhydrazyl is contained in an aprotic organic solvent, a charge of 4 V or more is obtained. When used at a potential, a non-aqueous electrolyte secondary battery which is stable and has excellent charge-discharge cycle characteristics and excellent storage characteristics in a charged state can be obtained, but there is a problem that the discharge performance of the battery is significantly reduced.

For example, in the discharge performance at 4 V or less, there is a problem that the initial charge / discharge efficiency is reduced. In addition, there is a problem that the discharge performance at a high rate is significantly reduced.
In other words, the compound disclosed in Japanese Patent Application Laid-Open No. 9-326262 sacrifices the discharge performance of the battery, so that a practical battery cannot be obtained.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, the solvent of the electrolyte is nitrosobenzene. It is characterized by containing at least one kind of nitroso compound or nitrone compound excluding.

Further, the present invention provides the above non-aqueous electrolyte secondary battery, wherein the content of the nitroso compound or nitrone compound excluding nitrosobenzene in the non-aqueous electrolyte solvent is 0.001 to 0 in terms of a molar ratio to the entire electrolyte solution solvent. .1.

Further, the present invention provides the above non-aqueous electrolyte secondary battery, wherein the nitrone compound is 5,5-dimethyl-1-.
At least one selected from the group consisting of pyrroline-N-oxide, phenyl-Nt-butylnitrone, and 3,5-di-t-butyl-4-hydroxy-phenyl-Nt-butylnitrone Wherein the nitroso compound other than nitrosobenzene is 2-methyl-2-
It is characterized by being at least one selected from the group consisting of nitroso-propane, 2,4,6-tri-t-butylnitrosobenzene, and nitrosodurene.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, and uses a non-aqueous electrolyte obtained by dissolving a light metal salt in an organic solvent. .

The organic solvent used for the electrolyte includes ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide,
A polar solvent such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof may be used.

In the present invention, these organic solvents are
It is characterized by containing at least one kind of a nitroso compound or a nitrone compound excluding nitrosobenzene.
As a result, the decomposition and deterioration of the electrolyte after charging with time can be suppressed, and the charge-discharge cycle characteristics and the storage characteristics can be improved. In addition, it has excellent discharge characteristics at 4.2 V or less, and does not cause a decrease in charge / discharge efficiency and high-rate discharge performance at the first time.

Further, according to the present invention, the content of the nitroso compound or nitrone compound excluding nitrosobenzene in the non-aqueous electrolyte solvent is 0.005 in molar ratio with respect to the whole electrolyte solvent.
By setting the ratio to 1 to 0.1, an effect of suppressing the decomposition and deterioration of the electrolytic solution after charging over time can be obtained. When the content of these compounds was less than 0.001 in molar ratio, no improvement in overcharge performance was observed. Also,
No further improvement in battery performance was seen with more than 0.1 addition. Further, nitroso compounds or nitrone compounds other than nitrosobenzene are expensive, and therefore, it is industrially meaningless even if the amount of addition is increased.

In the present invention, as the nitrone compound, 5,5-dimethyl-1-pyrroline-N-oxide,
Phenyl-Nt-butylnitrone, 3,5-di-t-
At least one selected from the group consisting of butyl-4-hydroxy-phenyl-Nt-butylnitrone,
Nitroso compounds other than nitrosobenzene include 2-
Methyl-2-nitroso-propane, 2,4,6-tri-
By using at least one member selected from the group consisting of t-butylnitrosobenzene and nitrosodulene, a greater effect of suppressing the decomposition and deterioration of the electrolyte solution over time after charging can be obtained.

In the present invention, a lithium salt is preferably used as a salt of a light metal dissolved in an organic solvent. Lithium salts include LiPF ₆ , LiCl
O ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ CO ₂ , Li
CF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C
F ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (C
A salt such as OCF ₂ CF ₃ ) ₂ or a mixture thereof may be used.

Examples of the positive electrode active material include transition metal compounds such as manganese dioxide and vanadium pentoxide, transition metal chalcogen compounds such as iron sulfide and titanium sulfide, and composite oxides of these transition metals and lithium. Lix
MO ₂ (where M represents Co, Ni or Mn;
0.5 ≦ x ≦ 1) or a composite oxide of lithium and nickel, ie, LiNi
The positive electrode active material represented by pM1qM2rO ₂ (however, M
1, M2 is Al, Mn, Fe, Ni, Co, Cr, T
at least one element selected from i and Zn, or
Non-metallic elements such as P and B may be used. Furthermore, p + q + r =
1) can be used. In particular, high voltage,
A lithium-cobalt composite oxide and a lithium-cobalt-nickel composite oxide are preferable because a high energy density is obtained and the cycle characteristics are excellent.

Further, as the negative electrode, a material which can be doped or de-doped with an alkali metal such as lithium and sodium or an alkali metal such as lithium during charge / discharge reaction can be used. Examples of the latter include conductive polymers such as polyacetylene and polypyrrole, or coke,
Although carbon materials such as polymer charcoal and carbon fiber can be used, it is desirable to use a carbonaceous material because of its high energy density per unit volume. Examples of the carbonaceous materials include pyrolytic carbons, cokes (such as petroleum coke, pitch coke, and coal coke), carbon black (such as acetylene black), glassy carbon, and organic polymer material sintered bodies (organic polymer materials of 500 ° C
Fired in an inert gas stream or in a vacuum at the above appropriate temperature), carbon fiber, and the like.

[0020]

Next, preferred embodiments of the present invention will be described based on experimental results.

Embodiment 1 In a non-aqueous electrolyte secondary battery according to the present invention, an elliptical wound type power generating element comprising a positive electrode plate, a separator and a negative electrode plate is made of a metal-laminated resin film together with a non-aqueous electrolyte. It is housed in a heat-welded metal laminated resin film case, and its appearance is shown in FIG. In FIG. 1, 1 is a battery body, 2 is a battery case, 3
Is a positive electrode terminal, 4 is a negative electrode terminal, and 5, 6 and 7 are welded portions of the laminate case.

A lithium cobalt composite oxide was used as the positive electrode active material. The positive electrode plate is obtained by holding the above-mentioned lithium cobalt composite oxide as an active material on a current collector made of an aluminum foil having a thickness of 25 μm. The positive electrode plate is obtained by mixing 5 parts of polyvinylidene fluoride as a binder and 5 parts of acetylene black as a conductive agent together with 90 parts of an active material,
N-methyl-2-pyrrolidone was appropriately added to prepare a paste, which was then applied to both sides of the current collector material and dried.

The negative electrode plate has 90 parts of graphite (graphite) as a host material and polyvinylidene fluoride 10 as a binder on both sides of a current collector made of a copper foil having a thickness of 15 μm.
And N-methyl-2-pyrrolidone were added as appropriate to prepare a paste, which was then coated and dried.

The dimensions of the electrode plate are as follows.
Width 49mm, separator thickness 25μm, width 53mm,
The negative electrode plate had a thickness of 170 μm and a width of 51 mm, and lead terminals were welded to the positive electrode plate and the negative electrode plate, respectively. A polyethylene microporous membrane was used as a separator. The positive electrode plate, the separator, and the negative electrode plate are superimposed one after another, and are wound around the polyethylene winding core in an elliptical spiral shape so that the long side is parallel to the winding center axis of the power generation element. By turning, a power generating element having a size of 53 × 35 × 4 mm was obtained.

A polyethylene tape (here, an adhesive is applied on one side) is attached to a side wall portion of the power generation element parallel to the winding central axis of the power generation element, and the power generation element is stopped and fixed. did.

The power generating element is accommodated in a metal laminated resin film case, and the elliptical wound type power generating element is housed such that the center axis of the winding is perpendicular to the opening surface of the bag-shaped metal laminated resin film case. Fix and seal,
The electrolyte was vacuum-injected in such an amount that each electrode and the separator were sufficiently wetted and free electrolyte did not exist outside the power generating element.

As an electrolyte, 1.0 mol / l of L was added to a 4: 6 mixture (volume ratio) of ethylene carbonate and diethyl carbonate.
Using a solution of iPF _6. In this electrolyte, 6
Various nitroso compounds other than nitrosobenzene and nitrone compounds were added. For comparison, nitrosobenzene conventionally used was added. Lastly, a sealed non-aqueous electrolyte battery having a nominal capacity of 500 mAh was prototyped by performing sealing welding. The cell number of the prototype battery,
Table 1 summarizes the types and concentrations of the additives.

[0028]

[Table 1]

Using these batteries, a charge / discharge cycle test, a high rate discharge test, and an overcharge test were performed. The charge / discharge cycle test was performed up to 4.2 V at 1 C and further to 4.2 V.
The battery was charged at a constant voltage of V for a total of 3 hours, then discharged at 2.75 V at 1 C, and the ratio of the discharge capacity after 300 cycles to the initial discharge capacity was defined as the capacity retention rate.

In the high-rate discharge test, the battery was charged to 4.2 V at 1 C, and further to a constant voltage of 4.2 V for a total of 3 hours.
0.2 when discharged to 2.75V at C and 2C
The ratio of the 2C discharge capacity to the C discharge capacity was determined.

In the overcharge test, the battery was charged at a constant current up to 10 V at 1 A, and the state of the battery at that time was observed.

The results are shown in Table 2. Table 2
In Table 1, the capacity retention rate and the ratio of the 2C discharge capacity to the 0.2C discharge capacity each showed an average value of 10 cells.

[0033]

[Table 2]

Table 2 shows that the capacity retention after 300 cycles, which is one of the indexes indicating that the change with time of the electrolytic solution is small, was high, and good results were obtained in the high rate discharge test and the overcharge test. Has been found to be a battery containing an organic electrolyte in which the additive according to the present invention is added to the electrolyte at a molar ratio of 0.001 to 0.1. Further, even when the addition exceeds the ratio of 0.1, no superiority in performance was recognized, and therefore the addition concentration is preferably 0.001 to 0.1 in molar ratio.

Example 2 FIG. 2 shows a schematic cross section of the prismatic nonaqueous electrolyte secondary battery used in Example 2.

In FIG. 2, reference numeral 11 denotes a prismatic nonaqueous electrolyte secondary battery, 12 denotes an electrode group, 13 denotes a positive electrode, 14 denotes a negative electrode, 15 denotes a separator, 16 denotes a battery case, 17 denotes a lid, 18 denotes a safety valve, and 19 denotes a positive electrode. The terminal 20 is a positive electrode current collecting lead.

The prismatic non-aqueous electrolyte secondary battery 11 has a positive electrode 1 made by coating a positive electrode mixture containing a positive electrode active material on an aluminum current collector.
3, a flat electrode group 12 in which a negative electrode 14 in which a negative electrode mixture containing a negative electrode active material is applied to a copper current collector is wound via a separator 15, and a non-aqueous electrolyte solution containing an electrolyte salt. Is stored in the battery case 16.

A battery cover 17 provided with a safety valve 18 is attached to the battery case 16 by laser welding, a positive electrode terminal 19 is connected to the positive electrode 13 via a positive electrode current collecting lead 20, and a negative electrode 14 is connected to the inner wall of the battery case 16. And are electrically connected by contact.

The same positive electrode mixture as used in Example 1 was used. The positive electrode mixture was uniformly applied to a 30-μm-thick aluminum current collector, dried, then compression-molded by a roll press, and cut into a desired size to produce a positive electrode. Further, a polypropylene sheet as a reinforcing member was attached to the base of the take-out portion of the positive electrode lead.

The same negative electrode mixture as used in Example 1 was used. The negative electrode mixture was uniformly applied to a copper current collector having a thickness of 20 microns, dried, compression-molded by a roll press, and cut into a desired size to prepare a negative electrode.

The same separator and electrolyte as those used in Example 1 were used. For comparison, nitrosobenzene, which had been conventionally added, was also added at the same concentration to obtain a comparative battery.

A nitroso compound other than six kinds of nitrosobenzene and a nitrone compound were added to the electrolytic solution. Also,
For comparison, a conventionally used nitrosobenzene was added. Thus, width 30 mm, height 48 mm
A 6-mm-thick rectangular non-aqueous electrolyte secondary battery was produced. Table 3 summarizes the cell numbers, types of additives, and concentrations of the prototype batteries.

[0043]

[Table 3]

Using these batteries, a charge / discharge cycle test, a high rate discharge test, and an overcharge test were performed under the same conditions as in Example 1. Table 4 shows the results. In Table 4, the capacity retention rate and the ratio of the 2C discharge capacity to the 0.2C discharge capacity each indicated an average value of 10 cells.

[0045]

[Table 4]

Table 4 shows that the capacity retention after 300 cycles, which is one of the indexes indicating that the change with time of the electrolytic solution is small, was high, and good results were obtained in the high rate discharge test and the overcharge test. Has been found to be a battery containing an organic electrolyte in which the additive of the present invention is added to the electrolyte at a molar ratio of 0.001 to 0.1. Also,
Even when the addition exceeds the ratio of 0.1, no superiority in performance is recognized, so the addition concentration is 0.0
01 to 0.1 is preferred.

[0047]

By using the additive in the present invention,
Since the stability of the organic solvent contained in the battery is improved, a non-aqueous electrolyte secondary battery that is stable even at a charging potential of 4 V or more and has excellent charge / discharge cycle characteristics and storage characteristics in a charged state is obtained. In addition, the decomposition of the organic electrolyte was suppressed, and the cycle retention characteristics were improved. Further, at the time of discharging at 4 V or less, it is possible to suppress a decrease in the initial charge / discharge efficiency or a significant decrease in the discharge performance at a high rate. The industrial value of the present invention is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the appearance of a non-aqueous electrolyte secondary battery of Example 1.

FIG. 2 is a diagram showing a schematic cross section of a prismatic nonaqueous electrolyte secondary battery of Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery main body 2 Battery case 3 Positive electrode terminal 4 Negative electrode terminal 5, 6, 7 Welding part of laminate case 11 Rectangular nonaqueous electrolyte secondary battery 12 Electrode group 13 Positive electrode 14 Negative electrode 15 Separator 16 Battery case 17 Cover 18 Safety valve 19 Positive electrode 20 Positive current collecting lead

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the solvent of the electrolyte contains at least one of a nitroso compound or a nitrone compound excluding nitrosobenzene. Non-aqueous electrolyte secondary battery. 2. The content of a nitroso compound or a nitrone compound excluding nitrosobenzene in a non-aqueous electrolyte solvent is as follows:
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the molar ratio with respect to the entire electrolyte solvent is 0.001 to 0.1. 3. The method according to claim 1, wherein the nitrone compound is 5,5-dimethyl-
At least one member selected from the group consisting of 1-pyrroline-N-oxide, phenyl-Nt-butylnitrone, and 3,5-di-t-butyl-4-hydroxy-phenyl-Nt-butylnitrone 2. The method according to claim 1, wherein
Or the non-aqueous electrolyte secondary battery according to 2. 4. A nitroso compound other than nitrosobenzene is 2-methyl-2-nitroso-propane, 2,4,6
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is at least one selected from the group consisting of tri-t-butylnitrosobenzene and nitrosodulene.