JPH09213368A - Non-aqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress swell of a non-aqueous secondary battery and a drop of its charge/discharge performance by including tetrahydropyrane or its derivative in the electrolytic solution or solid electrolyte of the battery. SOLUTION: A non-aqueous secondary battery concerned is composed of a positive electrode consisting of oxide or chalcogenide of a transition metal and an electroconductive polyer, a negative electrode consisting of carbon occuluding and releasing lithium or a lithium alloy, and an organic electrolytic solution or highpolymer solid electrolyte, wherein tetrahydropyrane or its derivative is included in the electrolytic solution or solid electrolyte. This suppresses a swell of the battery at the time of charging caused by decomposition of the electrolytic solution and inhibits a drop of the charge/discharge performance generated in association with an increase of the internal impedance to lead to enhancement of the safety of the battery and its reliability.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode made of a transition metal oxide or chalcogenide, a conductive polymer, a negative electrode made of carbon or lithium alloy capable of absorbing and releasing lithium, and an electrolytic solution made of an organic electrolytic solution or a solid polymer electrolyte. The present invention relates to a non-aqueous secondary battery.

[0002]

2. Description of the Related Art Among non-aqueous secondary batteries in which the positive electrode is made of a transition metal oxide or chalcogenide and a conductive polymer, the positive electrode is particularly LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄
3.5-based on lithium electrode (Li / Li ⁺ ) standards such as
Batteries operating at 4.3V have been commercialized due to their high energy density. Carbonic acid esters such as ethylene carbonate, propylene carbonate, and diethyl carbonate are generally used as the solvent of the electrolytic solution of these batteries.

[0003]

In the conventional battery, the carbonic acid ester constituting the solvent of the electrolytic solution undergoes a chemical decomposition reaction on the surfaces of the positive electrode and the negative electrode, particularly during the first cycle charging, and CO, H Gases such as ₂ , CH ₄ , and C ₂ H ₆ are generated. This generated gas raises the internal pressure of the battery, so in flat batteries and prismatic batteries where the mechanical strength of the battery case is not particularly strong, the battery swells or the internal impedance of the battery rises, causing charging and discharging. There were problems such as being disabled.

[0004]

A 6-membered cyclic ether having excellent oxidation resistance and reduction resistance is used as a solvent of an electrolytic solution or a plasticizer of a polymer solid electrolyte. Specifically, tetrahydropyran or tetrahydro-γ-pyrone is used. Furthermore, when a hydrogen at the β-position is substituted with an alkoxyl group such as a methoxy group or an ethoxy group, tetrahydropyran, if a derivative of tetrahydro-γ-pyrone is used, the acid resistance is further improved,
It is preferable for suppressing gas generation due to decomposition of the solvent of the electrolytic solution.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION As an example, the positive electrode is LiCo.
In a non-aqueous secondary battery in which O ₂ and the negative electrode are 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 an electrolytic 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 the β position is substituted with a methoxy group or an ethoxy group is used.

Further, as an example of application to the plasticizer of the polymer solid electrolyte, a liquid random copolymer of polyethylene oxide (PEO) and polypropylene oxide (PPO) having a functional group such as acrylate at the terminal is added to the LiPF. After mixing a solution of tetrahydropyran, tetrahydro-γ-pyrone or a derivative thereof in which ₆ is dissolved, the polymer is cross-linked by, for example, electron beam irradiation to obtain a solid electrolyte.

[0007]

The present invention will now be described by way of examples, which should not be construed as limiting the invention. (Invention 1) N-methyl-pyrrolidone (hereinafter referred to as NMP) 10% solution of polyvinylidene fluoride (hereinafter referred to as PVDF) in a mixture of 90 parts by weight of LiCoO _{2 having an} average particle size of 10 μm and 5 parts by weight of Ketjenblack 50 Add parts by weight and knead. The kneaded product is applied on an aluminum foil current collector, dried, and pressed to obtain a positive electrode. The coating amount was adjusted so that the thickness of the coating layer after pressing was 100 μm.

Coke-based carbon particles 9 having an average particle size of 15 μm
50 parts by weight of a 10% solution of PVDF in NMP was added to 5 parts by weight, and the mixture was kneaded, applied on a copper foil current collector, and then dried.
Press to make a negative electrode. The thickness of the coating layer after pressing is 10
The coating amount was adjusted to be 0 μm. As the separator, 3 was used as a separator made of a polyethylene microporous film having a thickness of about 25 μm. 0.5 M L for electrolyte
An iPF ₆ -tetrahydropyran solution was used. Then, it is sealed by a conventional method to a size of 50 × 50 mm and a thickness of about 0.
The test cell was 5 mm.

This cell was charged to 4.2V at a charge rate of 0.5C, and then a constant voltage of 4.2V was charged. The total charging time was 3 hours. No swelling was observed in the battery after charging. The internal impedance was 12Ω. After that, the discharge rate is 0.5 C and the final voltage is 2.7.
The V discharge showed a discharge capacity of 50 mAh and a normal capacity.

(Invention 2) As an electrolytic solution, 0.5 M L
The battery configuration, test conditions, etc. were the same as those of the present invention 1 except that iPF ₆ -2,6 dimethoxydihydropyran was used. After charging, the battery did not swell and the internal impedance was 13Ω as in the case of the present invention 1. The subsequent discharge showed a discharge capacity of 47 mAh and a normal capacity.

(Invention 3) 0.5 M Li as an electrolytic solution
The battery configuration, test conditions, etc. were the same as those of the present invention 1 except that PF ₆ -tetrahydro-γ-pyrone was used. The internal impedance was 11Ω, the discharge capacity was 49 mAh, and good test results were obtained as in the case of the present inventions 1 and 2.

(Invention 4) 0.5 M Li as an electrolytic solution
The battery configuration, test conditions, etc. were the same as those of the present invention 1 except that PF ₆ -2,6 dimethoxydihydro-γ-pyrone was used.
With an internal impedance of 15Ω and a discharge capacity of 45 mAh, good test results were obtained as in the case of the present inventions 1 to 3.

(Invention 5) 30 parts by weight of a random copolymer of PEO and PPO having acrylate groups at both ends and having a molecular weight of about 10,000 is mixed with 70 parts by weight of a 0.5 M LiPF ₆ -2,6 dimethoxydihydropyran solution. It was mucus.

90 parts by weight of LiCoO _{2 having an} average particle size 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.
Apply this paste on aluminum foil with a thickness of approx.
Coated with 00 μm. The coating portion was irradiated with an electron beam to cure the coating portion to obtain a positive electrode.

Coke-based carbon powder 6 having an average particle size of 15 μm
0 parts by weight and 40 parts by weight of the mucus were kneaded into 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 portion was irradiated with an electron beam to cure the coating portion, thereby obtaining a negative electrode.

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. The paste was coated on the surface of the positive electrode to a thickness of about 50 μm and then irradiated with an electron beam to form a separator layer. The positive electrode thus produced, a separator,
After stacking the negative electrodes, the test cells were sealed in the same manner as in the first embodiment.

3. This test cell was charged at a charge rate of 0.2C.
It was charged up to 2V and further charged at a constant voltage of 4.2V. The total charging time was 8 hours. After charging, no swelling was observed in the cell, internal impedance was 28Ω, then
When discharged at a discharge rate of 0.2 C and a final voltage of 2.7 V, it showed a normal capacity of 49 mAh.

(Invention 6) The same battery configuration as in Invention 5 was used, except that 2,6 dimethoxydihydro-γ-pyrone was used as the plasticizer instead of 2,6 dimethoxydihydropyran, and the same test was conducted. I served. Internal impedance 31
Ω, discharge capacity of 47 mAh, and good results similar to those of the present invention 5 were obtained.

Comparative Example 1 0.5 M Li as an electrolyte
Other than using a PF ₆ -Popyrylene carbonate / dimethyl carbonate mixed system (hereinafter referred to as PC / DEC),
The configuration of the battery and the test conditions were the same as those of the first invention. After the charging, swelling was observed in the cell, the impedance increased to 1000Ω or more, and the subsequent discharge charging became impossible.

Comparative Example 2 PC / DEC as a plasticizer
The configuration of the battery and the test conditions were the same as those of the present invention 5 except that the above was used. After the charging, swelling was observed in the cell, the impedance increased to 1000Ω or more, and the subsequent discharge charging became impossible.

[0021]

INDUSTRIAL APPLICABILITY The present invention relates to a non-aqueous secondary battery in which a negative electrode is made of carbon or a transition metal oxide or chalcogenide capable of inserting and extracting lithium. Swelling of the battery, which suppresses deterioration of charge / discharge performance due to increase in internal impedance, is effective for improving safety, reliability, and safety of the battery.
It is of high industrial value.

Claims (4)

[Claims] 1. A non-aqueous secondary battery containing tetrahydropyran or a derivative thereof in an electrolytic solution or a solid electrolyte. 2. The non-aqueous secondary battery according to claim 1, wherein the derivative is a tetrahydropyran derivative having an alkoxyl group introduced at the β-position. 3. A non-aqueous secondary battery containing tetrahydro-γ-pyrone or a derivative thereof in an electrolytic solution or a solid electrolyte. 4. The non-aqueous secondary battery according to claim 3, wherein the derivative is a tetrahydro-γ-pyrone derivative having an alkoxyl group introduced at the β-position.