JP2000012035A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wettability and conductivity of a carbon material relative to a nonaqueous electrolyte and suppress the generation of dendrite by using, as a negative-electrode active material, a mixture comprising a carbon material capable of storing/discharging lithium and a conductive material made up by coating surfaces of cores with a conductive layer of tin oxide. SOLUTION: For cores, particles of aluminum borate coated with titanium oxide, barium sulfate, or aluminum oxide and having spherical, plate-like, or fibrous shape are used. As a negative-electrode active material, a non graphitizable, an easily graphitizable carbon, or a graphite low in crystallinity, is used. A polyethylene oxide of an average molecular weight of 200 to 1,000 with ends changed into acrylate, or an ethylene-oxide additional body changed into acrylate of bisphenol A of an average molecular weight of 300 to 1,000, is used as a monomer, which is polymerized with an electrolyte, such as propylene carbonate and ethylene carbonate, by heating them or subjecting them to irradiation such as gamma rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a negative electrode used for a lithium battery.

[0002]

2. Description of the Related Art In recent years, lithium batteries having a high energy density have been used in the electronics field. In particular, the market for portable devices such as cellular phones and PHSs and small personal computers is rapidly expanding. Against this background, the development of smaller, lighter, and thinner lithium-ion batteries with higher functionality is expected.

At present, in a lithium ion battery, a carbon material capable of storing lithium is used as a negative electrode active material.

[0004] The carbon materials are roughly classified into two types: non-graphitic carbon materials and easily graphitic carbon materials. Difficult-graphite carbon materials differ from graphite in the form of lithium doping. In addition to the lithium capacity in the ionic state close to the covalent bond intercalating between the layers, the lithium capacity is considered to exist near the surface closer to the ionic state. As a result, the doping / undoping capacity is large. Also, with respect to the cycleability, it has good characteristics because the crystal orientation is poor and the crystallinity is low, so that anisotropy hardly occurs in the volume change due to expansion and contraction. However, there is a problem that the potential gradually changes as the discharge proceeds. On the other hand, the graphite-based carbon material has an advantage that it can be easily applied to equipment because it has a flat discharge potential.

[0005] However, the graphite-based carbon material expands and contracts with the occlusion and release of lithium ions, making it impossible for the carbon active materials to conduct electricity and isolating the active material. Particularly in the case of a thin battery, it is difficult to apply pressure, and there has been a problem that these phenomena lead to cycle deterioration.

[0006] In order to improve such a problem, a conductive material such as metal powder or carbon black has been added to a carbon material. By adding these conductive materials to the carbon material and performing charge and discharge, it was possible to suppress the isolation of the active material.However, since these conductive materials have poor wettability with the non-aqueous electrolytic solution, they were not charged. In some cases, current is concentrated on a certain portion to generate lithium dendrite, leading to cycle deterioration and poor storage characteristics.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a lithium ion battery having excellent cycle characteristics.

[0008]

SUMMARY OF THE INVENTION The present invention provides a carbon material capable of inserting and extracting lithium, by adding a conductive material having a core material coated with a tin oxide-based conductive layer on the surface of a core material, thereby making the carbon material non-aqueous. By improving the wettability with the electrolytic solution and the conductivity and suppressing the generation of dendrites, it is possible to provide a secondary battery having excellent cycle characteristics.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A mixture of a carbon material capable of inserting and extracting lithium and a conductive material having a core material coated with a tin oxide-based conductive layer is used as a negative electrode active material. It is composed of aluminum oxide, titanium oxide coated with aluminum borate, barium sulfate or aluminum oxide, and the particle shape is spherical, plate-like or fibrous. To form a lithium battery, the negative electrode is an electrolyte of the negative electrode mixture. The binder is a polymer that can be formed by polymerizing a monomer, and is prepared by polymerizing a mixture of the electrolyte and the monomer that is a precursor of the polymer that functions as the binder and the electrolyte. It is a lithium battery characterized by the above-mentioned.

[0010] The core material is not limited to the second aspect.

Examples of the negative electrode active material include, but are not limited to, hard graphite, easy graphite, and graphite having low crystallinity.

The monomer has an average molecular weight of 200 to 10
Examples include those obtained by acrylate-forming the terminal of polyethylene oxide of Example 00, and those obtained by acrylate-forming an ethylene oxide adduct of bisphenol A having an average molecular weight of 300 to 1,000.

Examples of the polymerization method include, but are not limited to, heating, irradiation of radiation such as ultraviolet rays, electron beams or gamma rays.

Examples of the electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate and γ-butyrolactone, dimethyl carbonate, and the like.
Chain carbonates such as diethyl carbonate, tetrahydrofuran, 1,2-dimethoxyethane, ethers such as methyl propionate, and esters alone or in a mixed solvent of two or more, for example, LiCF ₃ SO ₃ , LiBF ₄ ,
Examples thereof include those in which an electrolyte such as LiPF ₆ or LiAsF _{6 is} dissolved alone or in combination of two or more, but is not limited thereto.

[0015]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

(Invention 1) An electrolyte prepared by dissolving LiBF ₄ at 1 mol / l in γ-butyrolactone was prepared. The precursor monomer of the binder polymer of the electrode used was an acrylated bisphenol A ethylene oxide adduct. The average molecular weight is about 500.

The method for preparing the positive electrode is such that a mixture of 60 parts by weight of LiCoO ₂ , 1 part by weight of Ketjen black, 30 parts by weight of the above-mentioned electrolyte solution and 9 parts by weight of the above-mentioned monomer is used as a current collector. It was applied to an aluminum foil having a thickness of 50 μm and irradiated with an electron beam to perform polymerization. Incidentally, the electrode thickness was 155 μm.

In the negative electrode, 95 parts by weight of fibrous artificial graphite and 5 parts by weight of a conductive material whose surface is coated with tin oxide are mixed in advance with 60 parts by weight of the mixture. A paste obtained by mixing 10 parts by weight of the above-mentioned monomer and 10 parts by weight of the above-mentioned monomer was coated on a 35 μm-thick copper foil as a current collector, and irradiated with an electron beam to perform polymerization. The thickness of the electrode was 100 μm.

The electrolyte layer is prepared by impregnating a non-woven fabric made of polypropylene with a mixture of a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide and the above-mentioned electrolyte solution at a ratio of 3: 7, and irradiating with an electron beam to carry out polymerization. Was done. Incidentally, the thickness of the gel electrolyte layer was 45 μm.

After the prepared positive electrode / negative electrode / electrolyte was bonded and a hot melt adhesive was placed around the electrodes, three sides of the square were heat-sealed, and the other side was sealed under vacuum.

(Invention 2) An electrolyte prepared by dissolving LiBF ₄ at 1 mol / l in γ-butyrolactone was prepared. The precursor monomer of the binder polymer of the electrode used was an acrylated bisphenol A ethylene oxide adduct. The average molecular weight is about 500.

The method for preparing the positive electrode is as follows. A mixture of 60 parts by weight of LiCoO ₂ , 1 part by weight of Ketjen black, 30 parts by weight of the above-mentioned electrolyte solution and 9 parts by weight of the above-mentioned monomer is used as a current collector. It was applied to an aluminum foil having a thickness of 50 μm and irradiated with an electron beam to perform polymerization. Incidentally, the thickness of the electrode was 155 μm.

The negative electrode was prepared by previously mixing 95 parts by weight of fibrous artificial graphite and 5 parts by weight of a conductive material in which the surface of titanium oxide coated with aluminum borate was coated with tin oxide, and 60 parts by weight of the mixture. A paste obtained by mixing 30 parts by weight of the above-mentioned electrolytic solution and 10 parts by weight of the above-mentioned monomer was coated on a 35 μm-thick copper foil as a current collector, and irradiated with an electron beam to perform polymerization. . The electrode thickness is 100 μm
Met.

The electrolyte layer is formed by impregnating a non-woven fabric made of polypropylene with a mixture of a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide and the above-mentioned electrolyte solution at a ratio of 3: 7, and irradiating an electron beam to polymerize the non-woven fabric. Was done. Incidentally, the thickness of the gel electrolyte layer was 45 μm.

After the prepared positive electrode / negative electrode / electrolyte is bonded, a hot melt adhesive is placed around the electrodes, and then a square 3
One side was heat sealed and the other was sealed under vacuum.

(Invention 3) An electrolyte prepared by dissolving LiBF ₄ at 1 mol / l in γ-butyrolactone was prepared. The precursor monomer of the binder polymer of the electrode used was an acrylated bisphenol A ethylene oxide adduct. The average molecular weight is about 500.

The method for preparing the positive electrode is such that a mixture of 60 parts by weight of LiCoO ₂ , 1 part by weight of Ketjen black, 30 parts by weight of the above-mentioned electrolyte solution and 9 parts by weight of the above-mentioned monomer is used as a current collector. It was applied to an aluminum foil having a thickness of 50 μm and irradiated with an electron beam to perform polymerization. Incidentally, the thickness of the electrode was 155 μm.

The negative electrode was prepared by previously mixing 95 parts by weight of fibrous artificial graphite and 5 parts by weight of a conductive substance coating the surface of titanium oxide coated with barium sulfate with tin oxide.
A mixture obtained by mixing 60 parts by weight of the mixture, 30 parts by weight of the above-mentioned electrolyte solution and 10 parts by weight of the above-mentioned monomer to form a paste was applied on a 35 μm-thick copper foil as a current collector, and irradiated with an electron beam. To perform polymerization. The thickness of the electrode was 100 μm.

The electrolyte layer is formed by impregnating a non-woven fabric made of polypropylene with a mixture of a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide and the above-mentioned electrolyte solution at a ratio of 3: 7, and irradiating an electron beam. Polymerization was performed. Incidentally, the thickness of the gel electrolyte layer was 45 μm.

After the prepared positive electrode, negative electrode, and electrolyte are bonded together and a hot melt adhesive is placed around the electrodes, a square 3
One side was heat sealed and the other was sealed under vacuum.

Comparative Example 1 An electrolytic solution prepared by dissolving LiBF ₄ at 1 mol / l in γ-butyrolactone was prepared. The precursor monomer of the binder polymer of the electrode used was an acrylated bisphenol A ethylene oxide adduct. The average molecular weight is about 500.

The method of preparing the positive electrode is such that a mixture of 60 parts by weight of LiCoO ₂ , 1 part by weight of Ketjen black, 30 parts by weight of the above-mentioned electrolyte solution and 9 parts by weight of the above-mentioned monomer is used as a current collector. It was applied to an aluminum foil having a thickness of 50 μm and irradiated with an electron beam to perform polymerization. Incidentally, the thickness of the electrode was 155 μm.

The negative electrode is a current collector having a thickness of 35 μm, which is a paste obtained by mixing 60 parts by weight of fibrous artificial graphite, 30 parts by weight of the above-mentioned electrolytic solution and 10 parts by weight of the above-mentioned monomer.
Was coated on a copper foil, and irradiated with an electron beam to perform polymerization.
The thickness of the electrode was 100 μm.

The electrolyte layer is formed by impregnating a non-woven fabric made of polypropylene with a mixture of a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide and the above-mentioned electrolyte solution at a ratio of 3: 7, and irradiating the non-woven fabric with an electron beam. Polymerization was performed. Incidentally, the thickness of the gel electrolyte layer was 45 μm.

After the prepared positive electrode / negative electrode / electrolyte are bonded together and a hot melt adhesive is placed around the electrodes, a square 3
One side was heat sealed and the other was sealed under vacuum.

Comparative Example 2 An electrolytic solution prepared by dissolving LiBF ₄ at 1 mol / l in γ-butyrolactone was prepared. The precursor monomer of the binder polymer of the electrode used was an acrylated bisphenol A ethylene oxide adduct. The average molecular weight is about 500.

The method of preparing the positive electrode is as follows. A mixture of 60 parts by weight of LiCoO ₂ , 1 part by weight of Ketjen black, 30 parts by weight of the above-mentioned electrolytic solution and 9 parts by weight of the above-mentioned monomer is used as a current collector. It was applied to an aluminum foil having a thickness of 50 μm and irradiated with an electron beam to perform polymerization. Incidentally, the thickness of the electrode was 155 μm.

The negative electrode was prepared by previously mixing 95 parts by weight of fibrous artificial graphite and 5 parts by weight of acetylene black, and mixing 60 parts by weight of the mixture, 30 parts by weight of the above-mentioned electrolytic solution and 10 parts by weight of the above-mentioned monomer to form a paste. The resultant was coated on a 35 μm thick copper foil as a current collector, and irradiated with an electron beam to perform polymerization. The thickness of the electrode was 100 μm.

The electrolyte layer is formed by impregnating a non-woven fabric made of polypropylene with a mixture of a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide and the above-mentioned electrolytic solution at a ratio of 3: 7, and irradiating an electron beam to polymerize the non-woven fabric. Was done. Incidentally, the thickness of the gel electrolyte layer was 45 μm.

The prepared positive electrode / negative electrode / electrolyte are bonded together and a hot melt adhesive is placed around the electrodes.
One side was heat sealed and the other was sealed under vacuum.

The batteries of the present invention 1, the present invention 2, the present invention 3, the comparative examples 1 and 2 were subjected to a constant voltage constant current charge / discharge test. The test condition is a constant current of 0.2 CmA of charging current.
The battery was charged to 1 V, and when the voltage reached 4.1 V, the battery was charged at a constant voltage so that the battery voltage was maintained at 4.1 V. When the total charging time reached 8 hours, charging was stopped. After a pause of one hour, a constant current discharge was performed at 0.2 CmA with a discharge end voltage of 2.7 V. Thereafter, a cycle test was performed under these conditions.

FIG. 1 shows the cycle test results of the batteries of the present invention 1, the present invention 2, the present invention 3, the comparative examples 1 and 2. It can be seen that the cycle life of the present invention is significantly improved as compared with the comparative example. The reason for this is that by adding a conductive material coated with a tin oxide-based conductive layer to the negative electrode active material, the wettability and conductivity between the carbon material and the non-aqueous electrolyte are improved, and the active material is electrically isolated. It is considered that the cycle life was improved because the generation of dendrites was suppressed.

[0043]

As described above, according to the battery of the present invention, an electrically isolated active material is obtained by adding a conductive material having a core material coated with a tin oxide-based conductive layer to a carbon material capable of inserting and extracting lithium. And the wettability between the carbon material and the non-aqueous electrolyte is improved, and the generation of dendrites due to the concentration of current is suppressed, so that the cycle life can be improved.

[Brief description of the drawings]

FIG. 1 is a view showing cycle characteristics of lithium batteries of the present inventions 1, 2, and 3 and Comparative Examples 1 and 2.

Continued on the front page F term (reference) 5H003 AA00 AA04 BB01 BB02 BB04 BB14 BC01 BC02 BC05 5H014 AA02 EE08 EE10 5H029 AJ05 AK03 AL06 AL07 AM01 AM02 AM03 AM04 AM05 AM07 AM16 BJ04 DJ08 DJ15 DJ16 EJ03 EJ05

Claims (2)

[Claims] 1. A carbon material capable of inserting and extracting lithium,
A lithium battery, wherein a mixture of a conductive material having a core material coated with a tin oxide-based conductive layer is used as a negative electrode active material. 2. The core material is made of aluminum borate, titanium oxide coated with aluminum borate, barium sulfate or aluminum oxide, and the particle shape is spherical, plate-like or fibrous. The lithium battery according to claim 1, wherein