JPH1131513A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is superior in cycle characteristic. SOLUTION: A negative electrode 1, a separator 3, a positive electrode 2 and a separator 3 are laminated in this order and wound around a center pin 14 to form an electrode body. This electrode body is stored in a battery can 5, and insulating plates 4 are disposed at both the upper end lower faces of the electrode body. A positive electrode lead 13 is led out of a positive electrode current collector 11 and welded to a battery lid 7, and a negative electrode lead 12 is led out of a negative electrode current collector 10 and welded to the battery can 5. After an electrolyte in the battery can 5 has been filled, the battery can 5 is caulked through a sealing gasket 6. A safety valve device 8 and the battery lid 7 are therefore fixed so as to constitute a cylindrical nonaqueous electrolyte secondary battery. Polyvinylidene fluoride is used for positive electrode and negative electrode binders, and polyimide of 20% or less in the coefficient of cubic expansion is further mixed in the positive electrode binder at a composition of 5 wt.% to 90 wt.% or less, while aromatic polyamide is mixed in the negative electrode binder at the composition ratio of 1 wt.% or higher to 90 wt.% or lower.

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 a non-aqueous electrolyte secondary battery having excellent cycle characteristics in a high temperature environment.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has promoted higher performance, smaller size, and more portable electronic devices, and accordingly, there has been an increasing demand for higher energy density of batteries used in these electronic devices. ing. Conventionally, secondary batteries used in these electronic devices include nickel-cadmium batteries and lead batteries, but these batteries have a low discharge potential and sufficiently meet the demand for batteries with a high energy density. The fact is that it has not been done.

Recently, lithium secondary batteries have attracted attention as batteries satisfying these requirements, and have been actively researched and developed. However, a secondary battery using metal lithium or a lithium alloy as a negative electrode has been recognized as having problems with cycle life, safety, rapid charging performance, and the like, and has become a major obstacle to practical use. These problems include dissolution of metallic lithium as the negative electrode, dendrite formation during deposition,
It is considered to be caused by miniaturization and is only practically used in some coin-type batteries.

In order to solve these problems, research on a lithium ion secondary battery which is a non-aqueous electrolyte secondary battery using a negative electrode made of a material which can be doped and dedoped with lithium ions such as a carbonaceous material. Development is active. In this lithium ion secondary battery, lithium does not exist in a metal state, so there is no problem of cycle deterioration and safety caused by the negative electrode using the lithium ion secondary battery, and a lithium compound having a high oxidation-reduction potential is used for the positive electrode. As a result, the voltage of the battery can be increased, which meets the demand for a high energy density battery.

Further, the self-discharge is less than that of the nickel-cadmium battery, and the battery has excellent characteristics as a secondary battery. As a result, it has been widely used as a power source for portable electronic devices such as 8 mm VTRs, CD players, notebook computers, and cellular telephones.

However, the above-described lithium ion secondary batteries tend to have lower cycle characteristics in a high-temperature environment than those in a room temperature, and particularly in notebook-type computers and the like, the environment surrounding the batteries becomes high. Therefore, a lithium ion secondary battery having excellent cycle characteristics at high temperatures has been desired.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent cycle characteristics in a high temperature environment and high reliability.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in consideration of the above-mentioned problems. The present invention relates to a positive electrode using a lithium-containing compound, a negative electrode using a lithium-doped and undoped material, and In a non-aqueous electrolyte secondary battery comprising an electrolytic solution, as a binder of at least one of the positive electrode and the negative electrode, has polyvinylidene fluoride, further, the binder of the positive electrode is mixed with polyimide, while the binder of the negative electrode Constitutes a non-aqueous electrolyte secondary battery in which an aromatic polyamide is mixed.

The polyimide has a volume expansion coefficient of 20% or less, and the composition ratio of the polyimide mixed with the binder of the positive electrode is 5% by weight or more and 90% by weight or less.

Further, the composition ratio of the aromatic polyamide mixed with the binder of the negative electrode is set to 1% by weight or more and 90% by weight or less to solve the above problem.

According to the configuration of the non-aqueous electrolyte secondary battery of the present invention, the cycle characteristics in a high-temperature environment are improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies, the present inventors have found that a mixture of polyvinylidene fluoride and a polyimide having a volume expansion coefficient of 20% or less is used as a positive electrode binder. By using a mixture of aromatic polyamide as a negative electrode binder,
It was found that the cycle characteristics in a high temperature environment were improved.

The first reason that the positive electrode binder of the present invention improves cycle characteristics under a high temperature environment is that polyimide has excellent oxidation resistance and does not undergo oxidative decomposition even when used as a positive electrode binder for lithium ion batteries. No. Second, by adding a polyimide having a low volume expansion coefficient, even if the charge and discharge cycle is repeated under a high temperature environment,
This is because it is considered that a decrease in the adhesive force between the active material and the conductive agent, and the adhesive force between the mixture and the positive electrode current collector can be suppressed.

The reason why the negative electrode binder of the present invention improves the cycle characteristics under a high temperature environment is that by adding an aromatic polyamide, even if the charge and discharge cycle is repeated under a high temperature environment, the active material and the conductive agent can be removed. This is because it is considered that a decrease in the adhesive force of the mixture and the adhesive force between the mixture and the negative electrode current collector can be suppressed.

The volume expansion coefficient of the polyimide according to the present invention was determined by immersing a resin film of 1 cm × 1 cm × 2 mm in a 1: 1 mixed solvent of propylene carbonate and diethyl carbonate at 23 ° C. for 7 days. Defined as percentage.

First, a lithium-containing composite oxide Li _X MO ₂ (M is one or more transition metals) is used as the positive electrode active material. Li _X CoO ₂ , Li _X Ni
Lithium composite oxides such as O ₂ , Li _X Mn ₂ O ₄ , and Li _X Co _y Ni _{1 -y} O ₂ are preferred. These lithium composite oxides are, for example, starting materials such as lithium, cobalt, nickel, and manganese carbonates, nitrates, oxides, and hydroxides, and mixing them according to the composition. It is obtained by firing in a temperature range of 1000 ° C.

On the other hand, although a carbon material is used as the negative electrode active material, any material capable of doping and undoping lithium can be used, and a low crystalline carbon obtained by firing at a relatively low temperature of 2000 ° C. or less. Highly crystalline materials such as artificial graphite and natural graphite obtained by treating a material or a raw material that easily crystallizes at a temperature near 3000 ° C. are used. For example, pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and the like can be used.
Examples of the coke include pitch coke, needle coke, and petroleum coke. Examples of the fired organic polymer compound include, for example, those obtained by firing and carbonizing a furan resin or the like at an appropriate temperature. The (002) plane spacing is 0.370 nm or more, and the true specific gravity is 1.70 g / cc.
And in differential thermal analysis in an air stream of 70
A carbon material having no exothermic peak at 0 ° C. or higher is preferable.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as a supporting electrolyte and this is dissolved in an organic solvent is used. Here, as the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone,
Tetrahydrofuran, 2-methyltetrahydrofuran,
1,3-dioxolan, 4-methyl-1,3-dioxolan, sulfolane, methylsulfolane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and the like can be used.

As the electrolyte, LiClO ₄ , LiAs
F ₆ , LiPF ₆ , LiBF ₄ , LiB (C
_{6 H 5) 4, CH 3} SO 3 Li, CF 3 SO 3 Li, L
iN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ ,
LiCl, LiBr and the like can be used.

[0020]

FIG. 1 shows a non-aqueous electrolyte secondary battery and a positive electrode binder according to the present invention.
This will be described with reference to the configurations and characteristics measurement results of Comparative Examples 1 to 9 and Comparative Examples 1 to 9. Note that the present invention is not limited to these examples.

Example 1 A positive electrode was produced as follows. Cobalt carbonate and lithium carbonate were mixed at a ratio of Li / Co = 1, and calcined in air at 900 ° C. for 5 hours to obtain LiCoO ₂ . X-ray diffraction measurement of this material showed a good match with the JCPDS card.

89% by weight of this LiCoO ₂ , 6% by weight of graphite as a conductive agent, and 5% by weight of a mixture of polyvinylidene fluoride and polyimide as a binder to prepare a positive electrode mixture, which is used as a solvent. N-methyl-
The slurry was dispersed in 2-pyrrolidone to form a paste-like slurry. The slurry was applied to both surfaces of an aluminum foil serving as a positive electrode current collector, dried, and then compression-molded with a roller press to form a positive electrode. At this time, the mixing ratio of the mixture of polyvinylidene fluoride and polyimide was 95.0% by weight of polyvinylidene fluoride and 5.0% by weight of polyimide. In addition, NI1001 manufactured by Sony Chemical Co., Ltd. was used as the polyimide, and its volume expansion coefficient was 2%.

A negative electrode was produced as follows. As a negative electrode active material, petroleum pitch was used as a starting material, and after introducing 10 to 20% of a functional group containing oxygen, oxygen-crosslinking was performed, followed by firing at 1000 ° C. in an inert gas to obtain a glassy carbon material. A non-graphitizable carbon material having properties close to the above was used. 90% by weight of this non-graphitizable carbon material and 10% by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone as a solvent to form a paste. Slurried. Further, this slurry was applied to both surfaces of a copper foil serving as a negative electrode current collector, dried, and then subjected to compression molding with a roller press to form a negative electrode.

Next, as shown in FIG. 1, the negative electrode 1, the positive electrode 2 and the negative electrode 1, the positive electrode 2, the negative electrode 1, the positive electrode 2, and the negative electrode 1 were formed through a separator 3 made of a microporous polypropylene film having a thickness of 25 μm. The separator 3 was laminated in this order, and this was wound many times around the center pin 14 to produce a spiral electrode body.

The spirally wound electrode body manufactured in this manner is housed in a battery can 5, and an insulating plate 4 is formed on the upper and lower surfaces of the spirally wound electrode.
The aluminum positive electrode lead 13 was led out of the positive electrode current collector 11 and welded to the battery cover 7, and the nickel negative electrode lead 12 was drawn out of the negative electrode current collector 10 and welded to the battery can 5. .

Into the battery can 5, an electrolytic solution obtained by dissolving LiPF ₆ at a ratio of 1 mol / l in a mixed solvent of propylene carbonate 50% by volume and diethyl carbonate 50% by volume was injected. Then, by caulking the battery can 5 through the sealing gasket 6 coated with asphalt,
The safety valve device 8 and the battery cover 7 were fixed, and a cylindrical non-aqueous electrolyte secondary battery having a diameter of 18 mm and a height of 65 mm was produced.

Examples 2 to 4 A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the binder composition ratio between polyvinylidene fluoride and polyimide NV1001 was as shown in Table 1. Was prepared.

Comparative Examples 1 to 3 A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the binder composition ratio between polyvinylidene fluoride and polyimide NV1001 was as shown in Table 1. Was prepared.

[0029]

[Table 1]

Examples 5 to 8 Example 1 was repeated except that the binder was a mixture of polyvinylidene fluoride and polyimide E1 manufactured by Sony Chemical Co., Ltd., and the composition ratio was as shown in Table 2. In the same manner as in the above, a cylindrical nonaqueous electrolyte secondary battery was produced. Incidentally, the volume expansion coefficient of the polyimide E1 is 20%.

Comparative Examples 4 to 5 Example 1 was repeated except that the binder was a mixture of polyvinylidene fluoride and polyimide E1 manufactured by Sony Chemical Co., Ltd., and the composition ratio was as shown in Table 2. In the same manner as in the above, a cylindrical nonaqueous electrolyte secondary battery was produced.

[0032]

[Table 2]

Comparative Examples 6 to 9 The binder was a mixture of polyvinylidene fluoride and polyimide NIV1200 manufactured by Sony Chemical Co., Ltd., except that the composition ratio was as shown in Table 3.
A cylindrical non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1. The volume expansion coefficient of the polyimide NIV1200 is 3
4%.

[0034]

[Table 3]

Examples 1 to 5 produced as described above
8. Regarding the cylindrical nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 9, at each temperature of 23 ° C., 45 ° C., and 60 ° C., the charging voltage is 4.20 V, the charging current is 1000 mA, and the charging time is 2.5.
h, and then discharge current 700 mA,
Discharge was repeated under the condition of a final voltage of 2.75 V, and the ratio between the first discharge capacity and the 200th discharge capacity was determined. The results are shown in Tables 1 to 3 above. In addition, environmental temperature 23 ℃,
Measure the internal impedance of the battery at 1 KHz,
The results are also shown in Tables 1 to 3.

From the above results, a mixture of polyvinylidene fluoride and a polyimide having a volume expansion coefficient of 20% or less was used as the positive electrode binder, and the composition ratio of the polyimide in the binder was 5% by weight or more and 90% by weight or less. By doing so, it can be seen that a non-aqueous electrolyte secondary battery having a large initial charge capacity and excellent cycle characteristics under a high temperature environment can be obtained.

On the other hand, when the composition ratio of the polyimide was less than 5% by weight, the cycle characteristics in a high temperature environment were not improved. When the composition ratio of polyimide exceeded 90% by weight, the internal impedance of the battery increased, and the discharge capacity decreased. Furthermore, when a mixture of polyvinylidene fluoride and a polyimide having a volume expansion coefficient exceeding 20% was used as a positive electrode binder, the cycle characteristics in a high temperature environment were not improved.

In Examples 1 to 8, the volume expansion coefficient was 2
As polyimide of 0% or less, polyimide NIV1001 and E1 manufactured by Sony Chemical Co., Ltd. were used, but the polyimide is not limited to this.

Next, the nonaqueous electrolyte secondary battery and the negative electrode binder according to the present invention will be described with reference to FIG. 1 and the structures and the results of characteristic measurements of Examples 9 to 14 and Comparative Examples 10 to 13 prepared. explain. In addition, polyparaphenylene terephthalamide (hereinafter abbreviated as “PPTA”) is used as the aromatic polyamide to be mixed with the negative electrode binder.

Example 9 LiCoO ₂ obtained in the same manner as in Example 1 as a positive electrode
Was used. 91% by weight of this LiCoO ₂ , 6% by weight of graphite as a conductive agent, and 3% by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture, which was added to N-methyl-2-pyrrolidone as a solvent. The slurry was dispersed to form a paste-like slurry. The slurry was applied to both surfaces of an aluminum foil serving as a positive electrode current collector, dried, and then compression-molded with a roller press to form a positive electrode.

As the negative electrode, a non-graphitizable carbon material obtained in the same manner as in Example 1 was used. This non-graphitizable carbon material is
0% by weight, polyvinylidene fluoride as binder and P
A mixture of PTA was mixed at a ratio of 10% by weight to prepare a negative electrode mixture, and the mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a paste slurry. At this time, the mixing ratio of polyvinylidene fluoride and PPTA was 99.0% by weight: 1.0% by weight. Further, this slurry was applied to both surfaces of a copper foil serving as a negative electrode current collector, dried, and then subjected to compression molding with a roller press to form a negative electrode.

Further, a cylindrical non-aqueous electrolyte secondary battery similar to that of Example 1 was produced using the positive electrode and the negative electrode produced as described above.

Examples 10 to 14 Except that the binder composition ratio is as shown in Table 4,
A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 9.

Comparative Examples 10 to 13 Except that the binder composition ratio is as shown in Table 4,
A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 9.

[0045]

[Table 4]

Examples 9-1 produced as described above
4. Regarding the cylindrical non-aqueous electrolyte secondary batteries of Comparative Examples 10 to 13, the charging voltage is 4.20 V, the charging current is 1000 mA, and the charging time is 2.
The battery is charged under the condition of 5 h, and then the discharge current is 700 m
A, The discharge is repeatedly performed under the condition of a final voltage of 2.75 V,
The ratio between the first discharge capacity and the 200th discharge capacity was determined.
The results are shown in Table 4 above. In addition, environmental temperature 23 ℃,
Measure the internal impedance of the battery at 1 KHz,
Table 4 also shows the results.

From the above results, by using a mixture of polyvinylidene fluoride and an aromatic polyamide as a negative electrode binder and setting the composition ratio of the aromatic polyamide in the binder to 1% by weight or more and 90% by weight or less, It can be seen that a nonaqueous electrolyte secondary battery having a large initial charge capacity and excellent cycle characteristics under a high temperature environment can be obtained.

On the other hand, when the composition ratio of the aromatic polyamide was less than 1% by weight, the cycle characteristics in a high temperature environment were not improved. When the composition ratio of the aromatic polyamide exceeded 90% by weight, it was observed that the internal impedance of the battery increased and the discharge capacity decreased.

In Examples 9 to 14, PPTA was used as the aromatic polyamide, but the present invention is not limited to this.

Although Li _X CoO ₂ was used as the positive electrode active material in Examples 1 to 14 described above, the present invention is not limited to this. Li _X NiO ₂ , Li _X Mn ₂ O ₄ , Li _{X
X Co y Ni 1-y O} 2 and lithium composite oxides may be used. Further, it goes without saying that the present invention is not limited to a cylindrical battery, but may be used for a square battery, a flat battery, a coin battery, and a button battery.

[0051]

As is clear from the above description, a mixture of polyvinylidene fluoride and a polyimide having a volume expansion coefficient of 20% or less is used as a positive electrode binder, and the composition ratio of the polyimide in the binder is 5% by weight. When the content is 90% by weight or less, a mixture of polyvinylidene fluoride and an aromatic polyamide is used as a negative electrode binder, and the composition ratio of the aromatic polyamide in the binder is 1% by weight or more and 90% by weight or less. By doing so, it becomes possible to provide a nonaqueous electrolyte secondary battery having excellent cycle characteristics under a high temperature environment.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a nonaqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Insulating plate, 5
... battery can, 6 ... sealing gasket, 7 ... battery lid, 8 ... safety valve device, 10 ... negative electrode current collector, 11 ... positive electrode current collector, 12 ...
Negative electrode lead, 13 ... Positive electrode lead, 14 ... Center pin

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode using a lithium-containing compound, a negative electrode using a lithium-doped and undoped material, and a non-aqueous electrolyte. As at least one of the binders,
A non-aqueous electrolyte secondary battery comprising polyvinylidene fluoride, wherein a polyimide is mixed in the binder of the positive electrode, and an aromatic polyamide is mixed in the binder of the negative electrode. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polyimide has a volume expansion coefficient of 20% or less. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a composition ratio of the polyimide mixed with the binder of the positive electrode is 5% by weight or more and 90% by weight or less. . 4. The non-aqueous electrolyte solution according to claim 1, wherein the composition ratio of the aromatic polyamide mixed with the binder of the negative electrode is 1% by weight or more and 90% by weight or less. Next battery.