JP3580336B2 - Rechargeable battery - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a secondary battery using a non-aqueous electrolyte as an electrolyte or a secondary battery using a polymer gel electrolyte as an electrolyte. More specifically, the present invention relates to a Li _1-X MO ₂ (M is Co , Ni, Fe, V, and Mn).
[0002]
[Prior art]
A secondary battery using a non-aqueous electrolyte as the electrolyte or a polymer gel electrolyte as the electrolyte includes Li _1-X CoO ₂ , Li _1-X NiO ₂ , and Li _1-X Mn ₂ O ₄ as the positive electrode active material. In particular, a secondary battery using a non-aqueous electrolyte as an electrolyte and having an output voltage of about 4 V has been put into practical use as a high energy density lithium ion battery.
[0003]
In a secondary battery such as a lithium ion battery, Li _1-X CoO ₂ , Li _1-X NiO ₂ , and Li _1-X Mn ₂ O ₄ used as a positive electrode active material have a strong oxidizing action, and Since carbon or the like used as an active material has a strong reducing action, and a flammable organic solvent is used for the non-aqueous electrolyte, the activity increases when _X of Li _1-X increases due to overcharging. It is known that the reactivity with the non-aqueous electrolyte increases, and heat is generated when an excessive current flows due to a short circuit or the like.
[0004]
Therefore, in a secondary battery such as the above-mentioned conventional lithium ion battery, the upper limit of the charging voltage is set at the time of charging so that _X of Li _1-X does not become excessive, or a protection circuit is added to the secondary battery. This prevents excessive current from flowing due to overcharging or short circuit.
[0005]
[Problems to be solved by the invention]
In the above-described conventional secondary battery, the weight efficiency is reduced by the protection circuit added for improving the safety, and the _X of Li _1-X is prevented from becoming excessive. There was a problem that the capacity could not be secured.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention provides a method for preparing a positive electrode containing Li _1-X MO ₂ (M is at least one element selected from Co, Ni, Fe, V, and Mn) as a positive electrode active material. A secondary battery comprising a capture agent, which captures radicals generated on the surface of a peroxide represented by MO ₂ in Li _1-X MO _{2 of a} positive electrode active material by charging. Since this can be changed to a stable substance, it is possible to suppress the generated radicals from reacting with the electrolytic solution to generate heat.
[0007]
Also, the present invention provides the secondary battery, the radical scavenger is characterized in that it is arranged on the particle surface of the positive electrode active material, thereby, it is possible to reliably capture the generated radical .
[0008]
Also, the present invention provides the secondary battery, the radical scavenger is characterized in that contained in the electrolytic solution in the positive electrode, thereby, the generated radicals with heat by the reaction with the electrolyte solution This can be suppressed.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on the embodiments.
[0010]
FIG. 1 is a sectional view of a secondary battery according to an embodiment of the present invention, which is an example of a cylindrical lithium ion battery.
[0011]
In FIG. 1, reference numeral 1 denotes a positive electrode, which is obtained by kneading a mixed powder comprising a positive electrode active material, a conductive agent and a binder together with an electrolytic solution. Reference numeral 2 denotes a negative electrode, which is obtained by kneading a mixture of a negative electrode active material and a binder together with an electrolytic solution. Reference numeral 3 denotes a separator which contains an electrolytic solution and is spirally wound together with the positive electrode 1 and the negative electrode 2 while being interposed between the positive electrode 1 and the negative electrode 2. The spirally wound electrode group is housed in a battery case 4 also serving as a negative electrode terminal, and a gasket 6 is arranged at an open end of the battery case 4 to be electrically connected to the positive electrode 1. 5 sealed. Reference numeral 7 denotes a safety valve, and reference numeral 8 denotes a PTC element, which prevents an abnormal rise in battery temperature and internal pressure.
[0012]
(Battery 1 of the present invention)
LiNiO ₂ powder as a positive electrode active material having 1% by weight of trivalent iron chloride as a radical scavenger disposed on the surface thereof; acetylene black as a conductive agent having a weight ratio of 5% to the positive electrode active material; A mixed powder composed of polyvinylidene fluoride as a binder having a weight ratio of 5% with respect to the positive electrode active material is kneaded with an electrolytic solution obtained by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate and dimethyl carbonate. A negative electrode current collector made of a copper foil is prepared by kneading a mixture of carbon particles as a negative electrode active material and a binder used for the positive electrode 1 on both surfaces of a positive electrode current collector made of A negative electrode group is formed by spirally winding a negative electrode 2 coated on both surfaces of a positive electrode 1 and a negative electrode 2 with a separator 3 made of a polyethylene film having micropores interposed between the positive electrode 1 and the negative electrode 2. Formed, was prepared present battery 1 was sealed by a lid 5 is housed in the container 4. Incidentally, trivalent iron chloride as a radical capturing material arranged in the LiNiO ₂ powder was immersed in an acetone solution of trivalent iron chloride LiNiO ₂ powder, in which was deposited by drying.
[0013]
In the above-described battery 1 of the present invention, LiNiO ₂ powder containing 1% by weight of trivalent iron chloride as a radical scavenger was used as a positive electrode active material, but if the weight ratio was 0.5% or less, radical The effect of trapping is reduced, and if it is 5% or more, the movement of ions is hindered. In addition, acetylene black as a conductive agent was distributed in 5% by weight but may be 1 to 10% in weight ratio, and polyvinylidene fluoride as binder was distributed in 5% in weight ratio but 2% in weight ratio. It is sufficient if it is 10% or less. Although trivalent iron chloride was dissolved in acetone, it may be dissolved in methyl ethyl ketone, tetrahydrofuran, or dimethoxyethane other than acetone.
[0014]
(Invention Battery 2)
Instead of disposing trivalent iron chloride as a radical scavenger on the surface of the positive electrode active material of the battery 1 of the present invention, α, α′-diphenyl-β-picrylhydrazyl as a radical scavenger is added to the positive electrode 1. A battery 2 of the present invention was prepared, which was the same as the battery 1 of the present invention, except that it was dissolved in a mixed solvent of the contained electrolyte so that the weight ratio to the positive electrode active material was 1%.
[0015]
(Conventional battery)
A conventional battery was prepared which was the same as the battery 1 of the present invention except that the radical scavenger was not disposed on the surface of the positive electrode active material.
[0016]
(Evaluation test 1)
The above-described batteries 1 and 2 of the present invention and the conventional battery were charged at a constant current of 0.5 C until the terminal voltage reached 4.3 V, then charged at a constant voltage of 4.3 V, and then short-circuited. In Nos. 1 and 2, the internal pressure did not increase and the safety valve did not operate, whereas in the conventional battery, it was recognized that the safety valve operated due to the internal pressure increase.
[0017]
(Evaluation test 2)
Next, the above-described batteries 1 and 2 of the present invention and the conventional battery were charged at a constant current of 0.5 C until the terminal voltage reached 4.3 V, and then charged at a constant voltage of 4.0 V, and then charged at a constant voltage of 4.0 V. The batteries charged at a constant voltage were prepared, and each was discharged at a constant current of 0.5 C to a final voltage of 2.7 V to compare the discharge capacities. The batteries 1 and 2 of the present invention were charged at a constant voltage of 4.0 V. All batteries were 510 mAh, and those charged at a constant voltage of 4.3 V were 560 mAh for the battery 1 of the present invention, and 550 mAh for the battery 2 of the present invention. For the battery, the one charged at a constant voltage of 4.0 V was 490 mAh, and the one charged at a constant voltage of 4.3 V was 560 mAh, but the one charged at a constant voltage of 4.3 V had the safety valve operated at the end of charging. Recognized It was.
[0018]
(Evaluation test 3)
Next, the batteries 1 and 2 of the present invention and the conventional battery prepared in the evaluation test 2 were heated on a hot plate at 200 ° C. and examined for changes. When the conventional battery charged at a constant voltage of 4.3 V operated the safety valve. However, no change was observed in the other batteries.
[0019]
From the evaluation tests 1 to 3 described above, it is considered that there is no problem in safety when the conventional battery is charged at a constant voltage of 4.0 V at the expense of a decrease in discharge capacity. It has been found that when the battery is charged at a constant voltage of 4.3 V without sacrificing, a problem occurs in safety. On the other hand, in the batteries 1 and 2 of the present invention, it was found that there was no problem in safety even when the battery was charged at a constant voltage of 4.3 V to increase the discharge capacity.
[0020]
In the embodiment described above, the radical scavenger may be disposed on the surface of the particles of the positive electrode active material as in the battery 1 of the present invention, or the radical scavenger may be contained in the electrolyte in the positive electrode as in the battery 2 of the present invention. Although effective, it may be placed on the surface of the particles of the positive electrode active material and may be included in the electrolyte solution in the positive electrode. It is preferable to dissolve the radical scavenger in a solvent when preparing the electrolytic solution when the electrolytic solution is included.
[0021]
Examples of the radical scavenger include tetraethyl-p-phenylenediamine, in addition to trivalent iron chloride such as Battery 1 of the present invention and α, α′-diphenyl-β-picrylhydrazyl such as Battery 2 of the present invention. Hydroquinone, quinone, t-butylcatechol, chloranil, dimethylcarbamic acid and the like can be used.
[0022]
Further, in the above-described embodiment, a secondary battery using a non-aqueous electrolyte as an electrolyte has been described. However, a secondary battery using a polymer gel electrolyte composed of polymethyl methacrylate or polyacrylonitrile and an electrolyte as an electrolyte is described. Even in a battery, the same effect can be obtained by disposing a radical scavenger on the particle surface of the positive electrode active material.
[0023]
【The invention's effect】
As described above, the secondary battery according to the present invention can improve safety without lowering the discharge capacity, and thus contributes to an increase in discharge capacity and an improvement in safety in a secondary battery such as a lithium ion battery. The big thing is.
[Brief description of the drawings]
FIG. 1 is a sectional view of a secondary battery according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery case 5 Cover 6 Gasket 7 Safety valve 8 PTC element

Claims (3)

A terminal containing, as a positive electrode active material, a positive electrode containing Li _1-X MO ₂ (M is at least one element selected from Co, Ni, Fe, V, and Mn) and trivalent iron chloride as a radical scavenger ; A secondary battery that is used after being charged at a constant voltage of 4.3 V. 2. The secondary battery according to claim 1, wherein a positive electrode active material in which the trivalent iron chloride is arranged in a weight ratio of 0.5 to 5% is used. 3. 3. The secondary battery according to claim 1, wherein a non-aqueous electrolyte or a polymer gel electrolyte is used.

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