JP3567954B2 - Non-aqueous secondary battery - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous secondary battery in which the positive electrode is a transition metal oxide or chalcogenide, a conductive polymer, the negative electrode is carbon or a lithium alloy capable of inserting and extracting lithium, and the electrolyte is an organic electrolyte or a polymer solid electrolyte. Things.
[0002]
[Prior art]
Among nonaqueous secondary batteries in which the positive electrode is made of a transition metal oxide or chalcogenide or a conductive polymer, the positive electrode is particularly based on a lithium electrode (Li / Li ⁺ ) such as LiCoO ₂ , LiNiO ₂ , or LiMn ₂ O _4. Batteries operating at 3.5 to 4.3 V have attracted attention because of their high energy density and have been commercialized. These ethylene carbonate Ne chromatography TMG as a solvent of the electrolyte of the battery, propylene carbonate ne over preparative, carbonic esters such as diethyl carbonate Ne over bets are commonly used.
[0003]
[Problems to be solved by the invention]
In the conventional battery, particularly at the time of charging in the first cycle, a chemical decomposition reaction of the carbonate ester constituting the solvent of the electrolytic solution occurs on the surfaces of the positive electrode and the negative electrode, and CO, H ₂ , CH ₄ , C ₂ H ₆ Gas is generated. Because the generated gas increases the internal pressure of the battery, the battery swells and the internal impedance of the battery increases, especially in flat batteries and square batteries, where the mechanical strength of the battery case cannot be increased. There were problems such as becoming impossible.
[0004]
[Means for Solving the Problems]
As a solvent for the electrolytic solution or a plasticizer for the solid polymer electrolyte, a 6-membered cyclic ether having excellent oxidation resistance and reduction resistance is used. Specifically, tetrahydropyran or tetrahydro-γ-pyrone is used.
Further, when a derivative of tetrahydropyran or tetrahydro-γ-pyrone in which the hydrogen at the β-position is substituted with an alkoxyl group such as a methoxy group or an ethoxy group is used, the acid resistance is further improved, and the gas resulting from the decomposition of the solvent of the electrolytic solution is used. It is preferable for suppressing generation.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
As an example, in a non-aqueous secondary battery in which the positive electrode is made of LiCoO ₂ and the negative electrode is made of carbon capable of inserting and extracting lithium, a solution of tetrahydropyran, tetrahydro-γ-pyrone or a derivative thereof in which LiPF ₆ is dissolved in the electrolyte solution Is used. As the derivative, 2,6 dimethoxy or 2,6 diethoxydihydropyran, 2,6 dimethoxy, or 2,6 diethoxydihydro-γ-pyrone in which the hydrogen at position β is substituted with a methoxy group or an ethoxy group is used.
[0006]
In addition, as an example of application to the plasticizer of the polymer solid electrolyte, LiPF ₆ is dissolved in a liquid random copolymer of polyethylene oxide (PEO) and polypropylene oxide (PPO) having a functional group such as acrylate at the end. After mixing the thus-prepared solution of tetrahydropyran, tetrahydro-γ-pyrone or a derivative thereof, the polymer is crosslinked by, for example, irradiation with an electron beam to obtain a solid electrolyte.
[0007]
【Example】
Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.
(Invention 1)
To a mixture of 90 parts by weight of LiCoO _{2 having an} average particle diameter of 10 μm and 5 parts by weight of Ketjen black, 50 parts by weight of a 10% solution of N-methyl-pyrrolidone (hereinafter referred to as NMP) of polyvinylidene fluoride (hereinafter referred to as PVDF) is added. , Knead. The kneaded material is applied on an aluminum foil current collector, dried, and pressed to obtain a positive electrode. The amount of coating was adjusted so that the thickness of the coating layer after pressing was 100 μm.
[0008]
To 95 parts by weight of coke-based carbon particles having an average particle size of 15 μm, 50 parts by weight of a 10% solution of PVDF in NMP is added, kneaded, applied on a copper foil current collector, dried, and pressed to form a negative electrode. The amount of coating was adjusted so that the thickness of the coating layer after pressing was 100 μm.
As the separator 3, a separator made of a polyethylene microporous film having a thickness of about 25 μm was used.
The electrolyte used was a 0.5 M LiPF ₆ -tetrahydropyran solution. Next, the test cell was sealed by a conventional method to obtain a test cell having a size of 50 × 50 mm and a thickness of about 0.5 mm.
[0009]
This cell was charged to 4.2 V at a charge rate of 0.5 C, and then was charged at a constant voltage of 4.2 V. The total charging time was 3 hours. No swelling was observed in the battery after charging. The internal impedance was 12Ω. Thereafter, a discharge capacity of 50 mAh and a normal capacity were exhibited at a discharge rate of 0.5 C and a discharge voltage of 2.7 V.
[0010]
(Invention 2)
Except that 0.5 M LiPF ₆ -2,6 dimethoxydihydropyran was used as the electrolytic solution, the battery configuration, test conditions, and the like were the same as those of the first invention. After charging, the battery did not swell and the internal impedance was 13Ω as in the case of Invention 1. The subsequent discharge showed a normal discharge capacity of 47 mAh.
[0011]
(Invention 3)
Except that 0.5 M LiPF ₆ -tetrahydro-γ-pyrone was used as the electrolytic solution, the battery configuration, test conditions, and the like were the same as those of the first invention. The internal impedance was 11Ω and the discharge capacity was 49 mAh, which was the same as the results of the present inventions 1 and 2 and good test results.
[0012]
(Invention 4)
Except that 0.5 M LiPF ₆ -2,6 dimethoxydihydro-γ-pyrone was used as the electrolytic solution, the battery configuration, test conditions, and the like were the same as those of the first invention. The internal impedance was 15Ω, the discharge capacity was 45 mAh, and good test results were obtained as in the case of the first to third inventions.
[0013]
(Invention 5)
Both ends by mixing LiPF ₆ -2,6-dimethoxy-dihydropyran solution 70 parts by weight of 0.5M in 30 parts by weight of a random copolymer having a molecular weight of about 10000 of PEO and PPO having an acrylate group, and a mucus-like.
[0014]
90 parts by weight of LiCoO _{2 having an} average particle diameter of 10 μm, 70 parts by weight of a mixed powder of 5 parts by weight of Ketjen black, and 30 parts by weight of the mucus were kneaded to form a paste. This paste was coated on an aluminum foil having a thickness of about 30 μm to a thickness of about 100 μm. The coating was irradiated with an electron beam and cured to obtain a positive electrode.
[0015]
60 parts by weight of a coke-based carbon powder having an average particle size of 15 μm and 40 parts by weight of the mucus were kneaded to form a paste. This paste was coated on a copper foil having a thickness of about 20 μm to a thickness of about 100 μm. The coating was irradiated with an electron beam and cured to obtain a negative electrode.
[0016]
50 parts by weight of the above-mentioned mucus and 50 parts by weight of fine alumina powder having a submicron particle size were kneaded to form a paste. This paste was coated on the surface of the positive electrode with a thickness of about 50 μm, and then irradiated with an electron beam to form a separator layer. After laminating the positive electrode, the separator and the negative electrode produced in this way, they were sealed in the same manner as in the present invention 1 to obtain a test cell.
[0017]
This test cell was charged at a charging rate of 0.2 C up to 4.2 V, and further charged at a constant voltage of 4.2 V. The total charging time was 8 hours.
After charging, no swelling was observed in the cell, and the cell was discharged at an internal impedance of 28Ω and a discharge rate of 0.2 C and a cutoff voltage of 2.7 V. As a result, a normal capacity of 49 mAh was shown.
[0018]
(Invention 6)
Except that 2,6 dimethoxydihydro-γ-pyrone was used in place of 2,6 dimethoxydihydropyran as the plasticizer, the battery configuration was the same as that of the fifth invention, and the same test was performed. The internal impedance was 31Ω and the discharge capacity was 47 mAh.
[0019]
(Comparative Example 1) LiPF of 0.5M ₆ as an electrolytic solution - except using flop Ropirenkabone over DOO / di et Chirukabone over preparative mixing system (hereinafter referred to as PC / DEC), the configuration of the battery, the test conditions present invention Same as 1. After charging, swelling was observed in the cell, and the impedance was increased to 1000Ω or more, so that subsequent discharging and charging became impossible.
[0020]
(Comparative Example 2)
Except that PC / DEC was used as the plasticizer, the configuration of the battery, the test conditions, and the like were the same as those of the fifth invention.
After charging, swelling was observed in the cell, and the impedance was increased to 1000Ω or more, so that subsequent discharging and charging became impossible.
[0021]
【The invention's effect】
The present invention is directed to a non-aqueous secondary battery in which the negative electrode is made of an oxide or chalcogenide of carbon or a transition metal capable of inserting and extracting lithium, and the battery swells due to decomposition of the electrolytic solution during the first cycle of charging, It suppresses a decrease in charge / discharge performance due to an increase in internal impedance, is effective for improving the safety, reliability, and safety of a battery, and has high industrial value.

Claims (3)

In the nonaqueous secondary battery in which the positive electrode is an oxide of a transition metal, a chalcogenide or a conductive polymer, the negative electrode is carbon capable of inserting and extracting lithium, and the electrolytic solution is an organic electrolytic solution or a polymer solid electrolyte, the electrolytic solution or the solid A non-aqueous secondary battery characterized in that the electrolyte does not contain a carbonate ester and contains a derivative of tetrahydropyran having an alkoxyl group introduced at the β-position . In the nonaqueous secondary battery in which the positive electrode is an oxide of a transition metal, a chalcogenide or a conductive polymer, the negative electrode is carbon capable of inserting and extracting lithium, and the electrolytic solution is an organic electrolytic solution or a polymer solid electrolyte, the electrolytic solution or the solid A non-aqueous secondary battery characterized in that the electrolyte does not contain carbonate and contains tetrahydro-γ-pyrone or a derivative thereof. The non-aqueous secondary battery according to claim 2 , wherein the derivative is a derivative of tetrahydro-γ-pyrone having an alkoxyl group introduced at the β-position.