JP2000021388A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery excellent in a large electric current discharge characteristic and a charge/discharge cycle characteristic by setting the atomic number ratio Co/F of Co to F determined from a relative sensitivity factor and F1s and Co2 p3/2 photoelectron intensity when a detecting angle from the surface by X-ray electron spectroscopy using an Al-Kαray in a positive electrode active material layer is a specific angle, to a specific range. SOLUTION: When a detecting angle from the surface is 90 deg., the atomic number ratio Co/F is 0.05 to 0.30. An insulator 2 is arranged in the bottom part of a bottomed cylindrical vessel 1 composed of stainless steel. An electrode group 3 is housed in the vessel 1 by spirally winding a belt-like material by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order so that the negative electrode 6 is positioned on the outside. Nonwoven fabric and a polypropylene microporous film are used as the separator 5. An electrolyte is housed in the vessel 1. An insulating sealing plate 8 is arranged in the upper opening part of the vessel 1, and the vicinity of the upper opening part is calked inside so that the sealing plate 8 is liquid tightly fixed to the vessel 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art Recent advances in electronic technology and packaging technology have made many electronic devices, such as personal computers and telephones, smaller and more portable. Accordingly, there is a demand for higher performance of a secondary battery as a power supply of these electronic devices.

In such a secondary battery, a negative electrode is made of carbonaceous material or a chalcogen compound which stores and releases lithium metal and lithium ions, and a positive electrode is made of LiTiS ₂ , Li
MoS ₂ , LiV ₂ O ₅ , LiV ₆ O ₁₃ , LiMnO
₄ , a compound such as LiCoO ₂ that undergoes a topochemical reaction with lithium, using LiClO ₄ , LiBF ₄ , Li
Lithium salts such as AsF ₆ are converted to propylene carbonate, 1,2-
Non-aqueous electrolyte secondary batteries using an electrolyte dissolved in an organic solvent such as dimethoxyethane, γ-butyrolactone, and tetrahydrofuran have been developed.Particularly, carbonaceous materials that occlude and release lithium ions in the negative electrode, such as graphite and spherical carbon, Lithium-ion secondary batteries using carbon fibers and the like are currently widely used.

At present, an electrode for a non-aqueous electrolyte secondary battery is prepared by adding an electrode active material to a solution in which a binder is dispersed in an organic solvent, and dispersing and mixing the resulting slurry onto a current collector. It is manufactured by rolling and drying to form a thin plate.

[0005] Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PV).
DF), ethylene-propylene-diene copolymer (EP
DM), styrene-butadiene rubber (SBR), and the like.

[0006] Among these binders, polyvinylidene fluoride is excellent in solubility resistance to an electrolyte, adhesion to a current collector, and ion conductivity, and is used as a binder for an electrode for a non-aqueous electrolyte secondary battery. Is one of the preferred materials.

By the way, a non-aqueous electrolyte secondary battery having more excellent large current discharge characteristics and charge / discharge cycle characteristics has been demanded at present. Not obtained.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery excellent in large current discharge characteristics and charge / discharge cycle characteristics.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above object, and as a result, the quality of the electrode characteristics varies depending on the distribution of the binder on the surface of the electrode active material layer. Was found. That is, the non-aqueous electrolyte secondary battery using an electrode in which the atomic ratio of a specific element in X-ray photoelectron spectroscopy (XPS), which is an index indicating the distribution state of the binder, is within a certain range, has capacity characteristics, It has been found that large current characteristics and cycle life characteristics are satisfied in a well-balanced manner.

That is, the first non-aqueous electrolyte secondary battery according to the present invention has a positive electrode active material layer including a binder of LiCoO ₂ and a vinylidene fluoride-based fluororesin formed on the surface of a current collector. X-ray photoelectron spectroscopy using Al-Kα radiation in a positive electrode active material layer in a non-aqueous electrolyte secondary battery composed of a non-aqueous electrolyte, a negative electrode including a substance that absorbs and releases lithium ions, and a non-aqueous electrolyte And Co2p _3/2 when the detection angle from the surface by the XPS method is 90 ° and the atomic ratio of Co and F (Co / F) determined from the photoelectron intensity and the relative sensitivity coefficient.
F) is 0.05 or more and 0.30 or less.

Further, the second non-aqueous electrolyte secondary battery according to the present invention has a positive electrode, an active material layer containing a carbonaceous material that occludes / releases lithium ions and a binder of vinylidene fluoride-based fluororesin. In a non-aqueous electrolyte secondary battery including a negative electrode formed on the surface of a current collector and a non-aqueous electrolyte, X-ray photoelectron spectroscopy (XPS) using Al-Kα radiation in the negative electrode active material layer The atomic ratio (C / F) of C and F obtained from the F1s and C1s photoelectron intensities and the relative sensitivity coefficient when the detection angle from the surface is 90 ° is 1.0 or more and 3.0 or less. Is a non-aqueous electrolyte secondary battery.

Hereinafter, first and second nonaqueous electrolyte secondary batteries (for example, cylindrical nonaqueous electrolyte secondary batteries) according to the present invention will be described with reference to FIG. FIG. 1 is a perspective view showing one configuration example of the nonaqueous electrolyte secondary battery of the present invention. The structure of the lithium secondary battery of the present invention is not limited to the structure shown in FIG.

A bottomed cylindrical container 1 made of, for example, stainless steel has an insulator 2 disposed at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 includes a positive electrode 4,
A belt-like material in which the separator 5 and the negative electrode 6 are laminated in this order is wound on a spiral so that the negative electrode 6 is located outside. As the separator 5, for example, a nonwoven fabric, a microporous polypropylene film, a microporous polyethylene film, a polyethylene-polypropylene microporous laminated film, or the like can be used.

An electrolyte is contained in the container 1. The insulating paper 7 having a central opening is placed above the electrode group 3 in the container 1. The insulating sealing plate 8 is disposed in the upper opening of the container 1 and the vicinity of the upper opening is caulked inward to fix the sealing plate 8 to the container 1 in a liquid-tight manner. The positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. One end of the positive electrode lead 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9. The negative electrode 6 is connected to the container 1 as a negative electrode terminal via a negative electrode lead.

Next, the electrolyte, the positive electrode 4 and the negative electrode 6 will be specifically described. a) Electrolyte The electrolyte has a composition in which an electrolyte is dissolved in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), for example, dimethyl carbonate (D
MC), linear carbonates such as methyl ethyl carbonate (MEC), diethyl carbonate (DEC),
Chain ethers such as 1,2-dimethoxyethane (DME) and diethoxyethane (DEE), tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-Me
Cyclic ethers such as THF) and crown ethers;
At least one selected from fatty acid esters such as butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethylsulfoxide (DMSO) can be used.

[0017] Among them, those composed of at least one selected from EC, PC and γ-BL, EC, PC and γ-B
L, DMC, MEC, DE
It is desirable to use a mixed solvent comprising at least one selected from C, DME, DEE, THF, 2-MeTHF, and AN. In particular, when a negative electrode containing a carbonaceous material that absorbs and releases lithium ions is used, from the viewpoint of improving the cycle life of the secondary battery including the negative electrode,
C and PC and γ-BL, EC and PC and MEC, EC and PC
And DEC, EC and PC and DEE, EC and AN, EC and M
EC, PC and DMC, PC and DEC, or EC and DE
It is desirable to use a mixed solvent composed of C.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (LiPF).
₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ), lithium bistrifluoromethylsulfonylimide [ LiN (CF ₃ SO ₂ )
₂ ] and the like. Among them L
It is preferable to use iPF ₆ , LiBF ₄ , and LiN (CF ₃ SO ₂ ) ₂ because conductivity and safety are improved.

The amount of the electrolyte dissolved in the non-aqueous solvent is 0.1.
It is preferred to be in the range of 5 mol / l to 2.0 mol / l. Next, the positive electrode and the negative electrode will be described. b) Positive Electrode The positive electrode is prepared by suspending a conductive agent and a binder as necessary in a positive electrode active material in an appropriate solvent, and mixing the mixture slurry on one side or both sides of a current collector substrate with a size larger than a desired size. It can be produced by applying the material to an area, drying it and forming it into a thin plate, and cutting it into a desired size. Also, pellets formed by molding a positive electrode active material together with a conductive agent and a binder,
In addition, the positive electrode active material is kneaded with a conductive material and a binder,
The positive electrode may be prepared by attaching the sheet to a current collector. A ball mill, a bead mill, a dissolver, a sand grinder, a roll mill, or the like is used as a dispersing device for preparing the slurry.

The thickness of the positive electrode active material layer formed on the current collector surface (excluding the thickness of the current collector) is desirably 50 μm or more and 200 μm or less. Examples of the current collector include an aluminum foil, a stainless steel foil, and a titanium foil. In particular, aluminum foil is most preferable because it is excellent in workability and inexpensive. At this time, the thickness of the foil is 10 μm.
When the thickness is at least 40 μm, the strength of the foil is high, and it is desirable in terms of increasing the capacity of the battery. c) Negative electrode The negative electrode is prepared by suspending a conductive agent and a binder as necessary in a negative electrode active material in an appropriate solvent, and applying the mixture slurry to a substrate serving as a current collector on one side or both sides of the negative electrode. It can be produced by applying the material to an area, drying it and forming it into a thin plate, and cutting it into a desired size. Further, a negative electrode 6 was prepared by forming a pellet obtained by molding the negative electrode active material together with the conductive agent and the binder, or kneading the negative electrode active material together with the conductive agent and the binder and forming a sheet into a current collector. You may. A ball mill, a bead mill, a dissolver, a sand grinder, a roll mill, or the like is used as a dispersing device for preparing the slurry.

The thickness of the negative electrode active material layer formed on the surface of the current collector (excluding the thickness of the current collector) is preferably not less than 50 μm and not more than 200 μm to facilitate the production of the electrode, It is desirable in terms of, for example, electrochemical characteristics.

As the current collector, for example, a copper foil, a nickel foil or the like can be used, but a copper foil is most preferable in consideration of electrochemical stability and flexibility at the time of winding.
The thickness of the foil at this time is preferably 8 μm or more and 20 μm or less, from the viewpoint of high strength of the foil and high capacity of the battery.

Further, the positive electrode and the negative electrode according to the first invention of the present invention will be described in detail. b-1) Positive electrode LiCoO ₂ is used as the positive electrode active material according to the first nonaqueous electrolyte secondary battery of the present invention. LiCoO ₂ is Li
_x CoO ₂ (0.05 ≦ x ≦ 1.10.) is also included.

LiCoO ₂ has an average diameter of 2 to 20 μm in consideration of the adhesion to the substrate and the electrochemical characteristics during electrode fabrication.
Preferably, the powder has a range of m. The specific surface area is preferably 0.5 to ² m ² / g. If the specific surface area is less than 0.5 m ² / g, the packing density of the positive electrode active material may be reduced during the production of the electrode, and a sufficient capacity may not be obtained. Furthermore, the charging / discharging efficiency may decrease due to the decrease in the reaction area. On the other hand, when the specific surface area is 2
If it exceeds m ² / g, the adhesiveness between the positive electrode active material and the substrate or between the positive electrode active materials during the production of the electrode may be reduced.

In the first nonaqueous electrolyte secondary battery of the present invention, a vinylidene fluoride-based fluororesin is used as a binder for the positive electrode. In the positive electrode active material layer, Al
-F by X-ray photoelectron spectroscopy (XPS) using Kα ray
1s and C2p C calculated from _3/2 photoelectron intensity and relative sensitivity coefficient
The atomic ratio (Co / F) of o to F is 0.05 or more and 0.30
It is as follows. This value is the value when the photoelectron detection angle is 90 ° from the surface during XPS measurement.

This atomic ratio (Co / F) is the atomic ratio of Co in the positive electrode active material LiCoO _{2 on the} electrode surface to F in the binder vinylidene fluoride-based fluororesin, that is, the positive electrode active material LiCoO _2. This is an index indicating how much the particles are covered with the binder vinylidene fluoride-based fluororesin.

If the atomic ratio (Co / F) is less than 0.05, the coating thickness or coverage of the binder on the surface of the positive electrode active material increases, the resistance increases, and the ion diffusivity decreases. As a result, the large current characteristics of the battery deteriorate. Further, the number of conductive paths between the electrode active materials is reduced, the utilization factor is reduced, and the cycle characteristics are also reduced. When the value is larger than 0.30, the amount of the binder decreases, and the binding force between the active materials,
The adhesion to the current collector cannot be maintained, and the battery characteristics deteriorate. It is more preferable that the content be in the range of 0.05 or more and 0.30 or less from the viewpoint of improving battery characteristics.

As the vinylidene fluoride-based fluororesin,
Polyvinylidene fluoride, a copolymer of vinylidene fluoride-6-propylene fluoride, a terpolymer of polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride,
Examples thereof include a vinylidene fluoride-pentafluoropropylene copolymer, a vinylidene fluoride-chlorotrifluoroethylene copolymer, and a copolymer obtained by copolymerizing another fluorine-based monomer with vinylidene fluoride.
Examples of such a copolymer of a fluorine-based monomer and vinylidene fluoride include a copolymer of tetrafluoroethylene-vinylidene fluoride and a terpolymer of tetrafluoroethylene-perfluoroalkylvinyl ether (PFA) -vinylidene fluoride. 3 of tetrafluoroethylene-hexafluoropropylene (FEP) -vinylidene fluoride
Copolymer, tetrafluoroethylene-ethylene-vinylidene fluoride copolymer, chlorotrifluoroethylene-vinylidene fluoride copolymer, chlorotrifluoroethylene-ethylene-vinylidene fluoride terpolymer,
A copolymer of vinyl fluoride and vinylidene fluoride can be given. Particularly preferred is polyvinylidene fluoride in view of battery characteristics and ease of electrode production. These binders may be used alone or may be mixed with other binders.

As an organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), ethyl acetate, acetone, toluene and the like can be used.

Examples of the conductive agent incorporated in the positive electrode include acetylene black, Ketjen black, graphite, carbon black and the like. When the total amount of the positive electrode active material and the conductive agent is 100 parts by weight, the amount of the binder may be in the range of 2 parts by weight to 10 parts by weight. Is preferred. If the amount is too large, the large current characteristics and the cycle characteristics may be deteriorated. If the amount is too small, the binding force between the active materials and the adhesion to the current collector cannot be maintained, and the battery characteristics deteriorate.

The amount of the conductive agent is preferably in the range of 1 to 20 parts by weight based on 100 parts by weight of the positive electrode active material. The amount of the organic solvent is preferably in the range of 50 parts by weight to 150 parts by weight based on 100 parts by weight of the total of the positive electrode active material, the binder, and the conductive agent. If the amount is too large, the stability of the slurry may be deteriorated, and it may be difficult to obtain an electrode having a uniform film thickness. If the amount is too small, the viscosity of the slurry may be increased and the coatability may be deteriorated.

The positive electrode according to the present invention preferably has a coating amount of only one side in the range of 100 to 400 g / m ^{2 from} the viewpoint of battery characteristics and ease of battery production. The atomic ratio (Co / F) of the electrode depends on the dispersion method, dispersion time, drying conditions of the electrode, particle size of the active material, specific surface area, and composition of the binder in the dispersion mixing step for preparing the slurry. The value changes. Therefore, it is necessary to appropriately optimize the manufacturing conditions according to the material, battery specifications, and the like.

C-1) Negative electrode As an active material of the negative electrode, for example, lithium ions are occluded.
Containing carbonaceous or chalcogen compounds to be released,
Examples thereof include those made of light metal. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions is preferable because battery characteristics such as cycle life of a secondary battery are improved.

Examples of the carbonaceous materials that occlude and release lithium ions include coke, carbon fibers, pyrolytic gas phase carbonaceous materials, graphite, fired resins, fired mesophase pitch-based carbon fibers, and fired mesophase spherical carbon. Can be. Above all, mesophase pitch-based carbon fiber or mesophase spherical carbon which is graphitized at 2500 ° C. or higher is preferable because the electrode capacity is increased.

The chalcogen compounds that occlude and release lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbSe).
₂ ) and the like. When such a chalcogen compound is used for the negative electrode, the capacity of the negative electrode is increased although the voltage of the secondary battery is reduced, so that the capacity of the secondary battery is improved. Furthermore, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like. Examples of the binder used at the time of manufacturing the negative electrode include polytetrafluoroethylene (PTFE), a vinylidene fluoride-based fluororesin such as polyvinylidene fluoride (PVdF), an ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene. Rubber (SBR) or the like can be used.

As an organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), acetone and the like are used. The amount of the binder is 2 to 1 based on 100 parts by weight of the negative electrode active material.
The range of 5 parts by weight is preferable in terms of battery characteristics, retention of electrode strength, and ease of electrode production.

In particular, when a carbonaceous material is used as the negative electrode active material, it is desirable to use polyvinylidene fluoride as the binder, and the compounding amount is 2 parts by weight with respect to 100 parts by weight of the negative electrode active material.
It is preferable that the content be in the range of 15 to 15 parts by weight from the viewpoint of maintaining battery characteristics and electrode strength.

The amount of the organic solvent is preferably in the range of 50 parts by weight to 150 parts by weight based on 100 parts by weight of the total of the negative electrode active material and the binder. If the amount is too large, the stability of the slurry may be deteriorated, and it may be difficult to obtain an electrode having a uniform film thickness. If the amount is too small, the viscosity of the slurry may be increased and the coatability may be deteriorated.

In the negative electrode according to the present invention, it is preferable that the coating amount on one side is in the range of 50 to 300 g / m ² in terms of battery characteristics.
It is preferable from the viewpoint of easy battery production. When a carbonaceous material is used as the negative electrode active material, it is preferable that the amount of coating on one side be in the range of 50 to 200 g / m ² in terms of battery characteristics or ease of battery production in the state where the negative electrode is prepared.

Further, the positive electrode and the negative electrode according to the second invention of the present invention will be described. b-2) Positive Electrode As the active material of the positive electrode, for example, lithium cobalt oxide (LiCoO ₂ , lithium nickel oxide (LiNiO 2)
₂ ), lithium manganese oxide (LiMnO ₂ , LiM
n ₂ O ₄ ). Among them, a positive electrode using lithium cobalt oxide is particularly preferable because it has excellent battery characteristics such as large current characteristics, cycle life, and charge / discharge efficiency.

The binder used in the production of the positive electrode is described in the column of polytetrafluoroethylene (PTFE), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), or b-1). Vinylidene fluoride-based fluororesin can be used. As the vinylidene fluoride-based fluororesin, polyvinylidene fluoride is particularly preferred in view of battery characteristics and ease of electrode preparation.
These binders may be used alone or may be mixed with other binders.

As an organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), ethyl acetate, acetone, toluene and the like are used.

Examples of the conductive agent to be incorporated in the positive electrode include acetylene black, Ketjen black, graphite, carbon black and the like. When the total amount of the positive electrode active material and the conductive agent is 100 parts by weight, the amount of the binder may be in the range of 2 parts by weight to 10 parts by weight. Is preferred. If the amount is too large, the large current characteristics and the cycle characteristics may be deteriorated. If the amount is too small, the binding force between the active materials and the adhesion to the current collector cannot be maintained, and the battery characteristics deteriorate.

The amount of the conductive agent is preferably in the range of 1 to 20 parts by weight based on 100 parts by weight of the positive electrode active material. The amount of the organic solvent is preferably in the range of 50 parts by weight to 150 parts by weight based on 100 parts by weight of the total of the positive electrode active material, the binder, and the conductive agent. If the amount is too large, the stability of the slurry may be deteriorated, and it may be difficult to obtain an electrode having a uniform film thickness. If the amount is too small, the viscosity of the slurry may be increased and the coatability may be deteriorated.

The positive electrode according to the present invention preferably has a coating amount of only one side in the range of 100 to 400 g / m ² in terms of battery characteristics and ease of battery production. C-2) Negative Electrode For the negative electrode active material according to the second nonaqueous electrolyte secondary battery of the present invention, a lithium ion-absorbing carbonaceous material is used. Examples of the carbonaceous material include coke, carbon fiber, pyrolysis gas phase carbon material, graphite, resin fired body, mesophase pitch-based carbon fiber, and fired body of mesophase spherical carbon. Above all, mesophase pitch-based carbon fiber or mesophase spherical carbon which is graphitized at 2500 ° C. or higher is preferable because the electrode capacity is increased.

The carbonaceous material has an average diameter of 3 in consideration of battery characteristics.
It is preferred that the powder be in the range of ５０50 μm. In the second nonaqueous electrolyte secondary battery of the present invention, a vinylidene fluoride-based fluororesin is used as a binder for the positive electrode.
In the negative electrode active material layer, the atomic ratio of C and F (C / F) obtained from the F1s and C2p3 _{/ 2} photoelectron intensity and the relative sensitivity coefficient by X-ray photoelectron spectroscopy (XPS) using Al-Kα radiation. F) is 1.0 or more and 3.0 or less. Note that XP
This is the value when the photoelectron detection angle is 90 ° from the surface during S measurement.

The atomic ratio (C / F) is the atomic ratio of C in carbon of the negative electrode active material on the electrode surface to F in the binder vinylidene fluoride-based fluororesin, that is, the carbon number of the negative electrode active material. This is an index indicating how much the particles are covered with the binder vinylidene fluoride-based fluororesin.

If the atomic ratio (C / F) is less than 1.0, the coating thickness or coverage of the binder on the surface of the negative electrode active material increases, the resistance increases, and the ion diffusivity decreases. As a result, the large current characteristics of the battery deteriorate. Further, the number of conductive paths between the electrode active materials is reduced, the utilization factor is reduced, and the cycle characteristics are also reduced. On the other hand, when the value is larger than 3.0, the amount of the binder decreases, and the binding force between the active materials and the adhesion to the current collector cannot be maintained. Yes, and the cycle characteristics deteriorate. From the viewpoint of battery characteristics, the ratio is preferably 1.2 or more and 2.5 or less.

As the vinylidene fluoride-based fluororesin,
Those described in column b-1) can be used. Particularly preferred is polyvinylidene fluoride in terms of battery characteristics and ease of electrode preparation. These binders may be used alone or may be mixed with other binders.

As an organic solvent for dispersing the binder, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or the like is used. Examples of the conductive agent to be mixed into the negative electrode and the positive electrode include those described in column C-1).

The amount of the binder is preferably in the range of 2 to 15 parts by weight, where the total of the negative electrode active material and the conductive agent is 100 parts by weight. If the amount is too large, the large current characteristics and the cycle life characteristics may be deteriorated. If the amount is too small, the electrode strength may be reduced and the electrode production may be difficult.

The amount of the conductive agent is preferably in the range of 1 to 20 parts by weight based on 100 parts by weight of the negative electrode active material. The amount of the organic solvent is preferably in the range of 50 to 150 parts by weight based on 100 parts by weight of the total of the positive electrode active material, the binder, and the conductive agent. If the amount is too large, the stability of the slurry may be reduced, and it may be difficult to obtain an electrode having a uniform film thickness. If the amount is too small, the slurry may have a high viscosity and coating may be difficult.

The positive electrode according to the present invention preferably has a coating amount on one side of 100 to 400 g / m ² in terms of facilitating battery production and improving battery characteristics. The atomic ratio (C / F) of the electrode depends on the dispersion method, dispersion time, drying conditions of the electrode, particle size of the active material, specific surface area, and composition of the binder in the dispersion and mixing step for slurry preparation. The value changes. Therefore, it is necessary to appropriately optimize the manufacturing conditions according to the material, battery specifications, and the like.

As described above, by using an electrode whose atomic ratio by XPS is controlled within a certain range as in the present invention, the resistance in the electrode is reduced,
Since the ion diffusivity is also improved, it is possible to provide a non-aqueous electrolyte secondary battery that satisfies large current discharge characteristics and cycle life characteristics in a well-balanced manner. Furthermore, it is more preferable to use both the positive electrode according to the first non-aqueous electrolyte secondary battery of the present application and the negative electrode according to the second non-aqueous electrolyte secondary battery of the present invention because excellent battery characteristics can be obtained.

[0056]

BEST MODE FOR CARRYING OUT THE INVENTION

[0057]

Embodiments of the present invention will be described below. (Example 1) (Preparation of positive electrode) First, an average particle diameter of 3 μm as a positive electrode active material was used.
Lithium cobalt oxide (LiCoO ₂ ) powder 100
3 parts by weight of acetylene black and 3 parts by weight of graphite, and 5 parts by weight of polyvinylidene fluoride (PVDF) (based on 100 parts by weight of active material and conductive agent in total) are N-methyl-2 parts by weight. -Pyrrolidone (NMP)
And mixed with a general-purpose disperser for 4 hours.

Next, the obtained slurry was applied to both sides of an aluminum foil (15 μm thickness) as a current collector substrate so that the coating amount per one side was 200 to 300 g / m ² .

The electrode thus obtained was rolled to obtain a positive electrode. (Preparation of Negative Electrode) First, mesophase pitch carbon fiber (MCF) using mesophase pitch as a raw material was carbonized at 1000 ° C. in an argon atmosphere, and then the average fiber length was 20 μm.
m, average fiber diameter 8 μm, particle size 1-80 μm, 90% by volume
Was appropriately pulverized so as to reduce the number of particles having a particle size of 0.5 μm or less (5% or less), and then graphitized at 3000 ° C. in an argon atmosphere to produce a carbonaceous material.

Next, a carbonaceous substance was added to a solution of polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone, and dispersed and mixed for 3 hours using a general-purpose dispersing machine. A slurry comprising 5 parts by weight of vinylidene chloride was prepared. This was applied to both surfaces of a copper foil as a current collector so that the application amount per one surface was 100 to 150 g / m ² , dried, and then pressed to produce a negative electrode.

(Assembly of Battery) A positive electrode, a separator made of a porous film made of polyethylene, and a negative electrode were respectively laminated in this order, and then spirally wound so that the negative electrode was located outside, thereby producing an electrode group.

As the electrolytic solution, a solution prepared by dissolving 1 M of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2) is used. Then, the electrode group and the electrolyte were stored in a stainless steel bottomed cylindrical container, respectively, to assemble the above-mentioned cylindrical non-aqueous electrolyte secondary battery (18650 size) shown in FIG.

(Example 2) The positive electrode was dispersed by a general-purpose disperser,
Except that mixing was performed for 2 hours, it was prepared in the same manner as in Example 1.

On the other hand, the negative electrode was produced in the same manner as in Example 1 except that the dispersion and mixing in the general-purpose disperser were performed for 2 hours. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

Example 3 A positive electrode was produced in the same manner as in Example 2. On the other hand, the negative electrode was produced in the same manner as in Example 1 except that the dispersion and mixing with a general-purpose disperser were performed for 4 hours. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

(Example 4) A positive electrode was made of L having an average particle size of 5 µm.
Except for using iCoO ₂ powder, it was produced in the same manner as in Example 1. On the other hand, the negative electrode was prepared in the same manner as in Example 2.

A cylindrical non-aqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode. (Example 5) A positive electrode was prepared in the same manner as in Example 4, except that dispersion and mixing with a general-purpose disperser were performed for 3 hours.

On the other hand, a negative electrode was produced in the same manner as in Example 3. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

(Example 6) A positive electrode was produced in the same manner as in Example 1 except that dispersion and mixing with a general-purpose disperser were performed for 1 hour.

On the other hand, a negative electrode was produced in the same manner as in Example 1. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

Example 7 A positive electrode was prepared in the same manner as in Example 1 except that a LiCoO ₂ powder having an average particle diameter of 10 μm as a positive electrode active material was used.

On the other hand, a negative electrode was produced in the same manner as in Example 1. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

Example 8 A positive electrode was prepared in the same manner as in Example 1 except that mixing and dispersion in a general-purpose dispersing machine was performed for 3 hours.

On the other hand, a negative electrode was produced in the same manner as in Example 1 except that mixing and dispersion were performed for 6 hours using a general-purpose disperser. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

Example 9 A positive electrode was produced in the same manner as in Example 8. On the other hand, a negative electrode was produced in the same manner as in Example 1 except that dispersion and mixing with a general-purpose disperser were performed for 1 hour.

A cylindrical non-aqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode. (Comparative Example 1) Dispersion and mixing with a general-purpose dispersing machine
Except for the time, it was prepared in the same manner as in Example 1. The negative electrode was produced in the same manner as in Example 8. A cylindrical non-aqueous electrolyte secondary battery (18
650 size).

(Comparative Example 2) The positive electrode was dispersed by a general-purpose disperser,
The preparation was performed in the same manner as in Example 7 except that the mixing was performed for 2 hours. The negative electrode was produced in the same manner as in Example 9. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

Comparative Example 3 A positive electrode was prepared in the same manner as in Comparative Example 1. The negative electrode was produced in the same manner as in Example 9. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode.

(Comparative Example 4) A positive electrode was prepared in the same manner as in Example 7. The negative electrode was produced in the same manner as in Example 8. A cylindrical nonaqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 by combining the positive electrode and the negative electrode. In Table 1,
The values such as the dispersion processing time of the positive electrode and the negative electrode are collectively shown.

[0080]

[Table 1]

(Large-Current Characteristics Test) The large-current discharge characteristics of the batteries of the above Examples and Comparative Examples were measured. As a method of defining the large current discharge characteristics, a method of defining a ratio of respective discharge capacities obtained when discharging at three current values is adopted here. That is, the nominal capacity of the battery is 1500
When the current of 1500 mA for discharging mAh in 1 hour is 1 C, the discharge capacity when discharging at 0.2 C (0.2
C) Discharge capacity when discharging at 1C (1C), 1.5C
, The discharge capacity (1.5 C) when discharged at 2 C, and the discharge capacity (2 C) when discharged at 2 C, respectively, and the discharge capacity (1 C) / discharge capacity (0.2
C), discharge capacity (1.5 C) / discharge capacity (0.2 C),
The value of the discharge capacity (3C) / discharge capacity (0.2C) is defined as the large current discharge capacity ratio, and will be used hereinafter in the text.

First, the measurement was performed at a charging current of 0.2 C (300 m
After charging at 4.2V constant voltage for 8 hours in A), 0.2C
The battery was discharged at 2.7 V cut. After three cycles of this charge / discharge, the discharge current was changed in the order of 1C, 1.5C, and 2C, and the large current characteristics were examined.

The large current discharge capacity ratio was calculated based on the discharge capacity of 0.2 C at the third cycle. (Cycle test) The cycle life characteristics of the batteries of the above Examples and Comparative Examples were measured. A charge / discharge cycle of charging at 4.2 A for 3 hours at a charging current of 1.5 A (1 C) under an environment of 20 ° C. and discharging at 1.5 A (1 C) to 2.7 V is repeated, and the capacity retention rate at that time Was examined.

Table 2 shows the Co / F atomic ratio by XPS analysis of the LiCoO2 positive electrode and the C / F atomic ratio by XPS of the carbon negative electrode. The discharge capacity (1 C) / discharge capacity (0.2 C), which is the ratio of the discharge capacity in the measurement of the large current characteristics of each battery, and the discharge capacity (1.5 C) / discharge capacity (0.
2C) and the value of discharge capacity (3C) / discharge capacity (0.2C) are also shown in Table 2.

Table 2 also shows the results of the cycle test of each battery. The value of the capacity retention ratio as a result of the cycle test is the discharge capacity at the first cycle (100
%) With respect to the discharge capacity at the 500th cycle.

In this example and the comparative example, the XPS
And the calculation of the atomic ratio were performed as follows.
The XPS measurement device is ESCA- manufactured by Gamma Data Sienta.
300 were used. Monochromatic Al-Kα ray (148
6.6 eV) and output 13 kV × 310 mA (4 k
w), measurement was performed with a photoelectron detection angle from the surface of 90 °. The pass energy was 150 eV and the energy step was 0.1 eV. Under the above conditions, F1s and Co2
p3 _{/ 2} , F1s photoelectron intensity, and C1s, F1s photoelectron intensity were measured. The background was approximated as a straight line, and the peak area was calculated. Note that the relative sensitivity coefficients for Al-Kα radiation are F1s = 4.43, C1s = 1.00, and Co2p _3/2 =
The atomic ratio was determined as 12.62.

[0087]

[Table 2]

As is clear from Table 2, the non-aqueous electrolysis of Examples 1 to 9 in which the Co / F atomic ratio of the positive electrode by XPS and the C / F atomic ratio of the negative electrode by the analytical method are within the scope of the present invention. With the liquid secondary battery, good results were also obtained for the large current discharge characteristics. In the embodiment, an example in which the present invention is applied to a cylindrical lithium secondary battery is described, but the present invention is also applicable to a prismatic lithium secondary battery.

[0089]

As described above, according to the non-aqueous electrolyte secondary battery of the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that satisfies a large current discharge characteristic and a cycle life characteristic in a well-balanced manner. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cylindrical lithium secondary battery according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Insulator, 3 ... Electrode group, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 7 ... Insulating paper, 8
... Insulating sealing plate, 9 ... Positive terminal, 10 ... Positive lead

Continued on the front page (72) Inventor Asako Sato 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Kawasaki Office (72) Inventor Masahiko Yoshiki 1st Kogashi-Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Stock Company Inside the Toshiba R & D Center (72) Inventor Takahisa Osaki 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term (reference) 5H014 AA02 AA04 EE02 EE08 EE10 HH00 HH01 5H029 AJ02 AJ05 AK03 AL07 AM03 AM05 AM06 BJ02 BJ14 EJ12 HJ00 HJ02

Claims (2)

[Claims] 1. A positive electrode having a positive electrode active material layer containing a binder of LiCoO ₂ and vinylidene fluoride-based fluororesin formed on the surface of a current collector; a negative electrode containing a substance that occludes and releases lithium ions; In a non-aqueous electrolyte secondary battery composed of an aqueous electrolyte and a non-aqueous electrolyte secondary battery, when the detection angle from the surface of the positive electrode active material layer by X-ray photoelectron spectroscopy (XPS) using Al-Kα radiation is 90 °, F1s and Co2p _3/2 The atomic ratio of Co and F (Co
/ F) is 0.05 or more and 0.30 or less. 2. A non-aqueous electrolyte comprising: a positive electrode; a negative electrode having an active material layer containing a carbonaceous substance that occludes and releases lithium ions and a binder of vinylidene fluoride-based fluororesin formed on the surface of the current collector; And C1s photoelectrons when the detection angle from the surface of the negative electrode active material layer by X-ray photoelectron spectroscopy (XPS) using Al-Kα radiation is 90 ° in the nonaqueous electrolyte secondary battery composed of A non-aqueous electrolyte secondary battery, wherein an atomic ratio (C / F) of C and F obtained from strength and a relative sensitivity coefficient is 1.0 or more and 3.0 or less.