JPH07312216A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To elongate battery life by using metal chalcogen compound formed by fluorinating at least a part of chalcogen as a positive electrode material. CONSTITUTION:Metal chalcogen compound is used as a positive electrode. Namely, metal chalcogen compound formed by fluorinating at least a part of chalcogen is used as the positive electrode. Oxide such as MnO2, V2O5, Cr3O8, MoO3, WO3, TeO2, V3O8, and LiCoO2, sulfide such as TiS2, FeS2, and Nb3S4, and selenide such as MoSe4, VSe2, and NbSe3 are used as metal chalcogen compound. These metal chalcogen compounds are treated by fluorine agent and fluorine gas and HF are used as fluorine agent. Leakage between electrolyte and the positive electrode is thus improved and oxygen generated by attack of F radical which is generated from LiPF6 used as solute of the electrolyte is reduced so as to suppress deterioration of the electrolyte and elongate its life.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery.

[0002]

2. Description of the Related Art With the recent rapid progress of electronic technology, the size and weight of electronic devices have been remarkably reduced, and there are great expectations for batteries as the power source for these devices. In other words, there are great expectations for batteries having high energy density such as small size and light weight, and superior storage properties. As one of the most promising battery systems that can meet these expectations, lithium batteries with lithium as a negative electrode are being actively developed. Lithium secondary batteries are recognized for their excellent characteristics, and VTR cameras,
It has rapidly penetrated the market as a portable power source for mobile phones and personal computers.

However, when metallic lithium is used as lithium, there is a drawback that a sufficient charge / discharge cycle life cannot be obtained despite its excellent characteristics. Therefore, it has been proposed to use a carbon-lithium intercalation compound obtained by intercalating lithium ions in various carbon materials as a negative electrode, and various carbon materials suitable for it and further various positive electrode materials have been investigated. .

[0004]

For example, it has been proposed to use graphite such as natural graphite or the like, a carbon material obtained by firing various resins or pitches as a negative electrode material, and various chalcogen compounds as a positive electrode material. However, in order to be applicable to large-sized batteries used for so-called distributed power storage systems such as electric vehicles and home nighttime power storage, further improvement in battery performance is required. .

[0005]

Therefore, the present inventor has conducted various studies to obtain a positive electrode material for a lithium secondary battery which can further extend the battery life, and arrived at the present invention. That is, the gist of the present invention is a lithium secondary battery using a metal chalcogen compound in which at least a part of chalcogen is fluorinated as a positive electrode material.

The present invention will be described in detail below. First, as the metal chalcogen compound in the present invention, Mn
_{O 2, V 2 O 5,} Cr 3 O 8, MoO 3, WO 3, Te
O ₂ , V ₃ O ₈ , oxides such as LiCoO ₂ , TiS ₂ ,
FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ S
_5, sulfides such as _{Cr 0. 25 V 0.75 S 2,} MoSe 4, V
Examples thereof include selenides such as Se ₂ and NbSe ₃ .

In the present invention, these metal chalcogen compounds are treated with a fluorinating agent. This treatment may be performed before or after molding as a positive electrode material. Examples of the fluorinating agent include fluorine gas and HF, and the treatment temperature is -10.
It is generally 0 ° C. to the melting point of the compound or less, for example, 10
About 0 to 300 ° C is suitable.

Further, the fluorination time may be a short time if the fluorinating agent is uniformly supplied to the metal chalcogen compound, and even if the time is long, a corresponding effect cannot be expected, and therefore it is usually 1 minute to 2 minutes. It is a daily processing time, more preferably 30 minutes or less. The fluorine partial pressure of the fluorinating agent is not particularly limited from pressurization to depressurization, but preferably 500 mmH
It is better to treat with g to 760 mmHg.

The fluorine gas and HF may be used alone or in combination, and may be used by mixing an inert gas such as nitrogen or argon. Furthermore, it can be used even if it contains a gas such as oxygen. The fluorinating agent-treated metal chalcogen compound thus obtained is
It has the following characteristics.

That is, the wettability of the electrolytic solution is improved and the deterioration due to oxygen is reduced. In the present invention, this metal chalcogen compound is used as the positive electrode. Regarding the electrolytic solution obtained by dissolving the electrolyte in the negative electrode and the non-aqueous solvent,
Conventionally, it may be one used for a non-aqueous secondary battery,
There is no particular limitation. Specifically, as the negative electrode, carbon,
Examples include graphite and conductive polymers. Examples of the electrolyte include LiClO ₄ , LiBF ₄ , and LiPF ₆ , and examples of the non-aqueous solvent that dissolves the electrolyte include propylene carbonate, tetrahydrofuran, 1,2-dimethoxyethane, dimethyl sulfoxide, dioxolane, dimethylformamide, dimethylacetamide, and A mixed solvent of two or more of these is used.

The separator is preferably a porous body for reducing the internal resistance of the battery, and a non-woven fabric such as polypropylene or an organic solvent resistant material such as a glass filter is used. The negative electrode, the positive electrode, the electrolytic solution, and the separator can form a secondary battery by a general method such as incorporation in a battery case plated with stainless steel or nickel.

As a battery structure, a spiral structure in which a band-shaped positive electrode and a negative electrode are spirally wound with a separator interposed therebetween, or a method in which a pellet-shaped positive electrode and a disk-shaped negative electrode are inserted into a button type case through a separator is adopted. However, when it is applied to a large-sized battery, it is general that the battery structure has a so-called rectangular structure and the unit cells are stacked.

[0013]

EXAMPLES The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example 1 As a positive electrode material, LiCoO ₂ having a diameter of about 10 μm was placed in a fluorination reactor, the inside of the container was kept in vacuum, and then a fluorine-containing gas (F ₂ 10 vol%, N ₂ 90 vol%).
Was introduced and fluorination treatment was performed at 200 ° C. and atmospheric pressure for 1 hour.

The obtained powder was mixed with acetylene black as a conductive material and fluororesin as a binder at 85: 10: 5.
The mixture was used by mixing at a weight ratio of
It heat-processed at -350 degreeC and it was set as the positive electrode. As the negative electrode material,
A lithium secondary battery was prepared by a conventional method using a carbon material and an electrolyte solution prepared by dissolving LiPF ₆ in propylene carbonate at a concentration of 1 mol / l.

Next, the discharge characteristics of the lithium secondary battery were measured. The measurement was usually performed under a constant current charge / discharge of 50 mA / g (negative electrode carbon standard), and the discharge capacity was defined as the capacity until the battery voltage dropped to 2.0V. For comparison, the measurement was performed under the same conditions also in the conventional lithium secondary battery using LiCoO ₂ which was not subjected to the fluorination treatment.
The results are shown in Table 1.

As is clear from Table 1, the lithium secondary battery of the present invention using fluorinated LiCoO ₂ is compared with the conventional lithium secondary battery using LiCoO ₂ which is not fluorinated. In a battery, the wetting of the electrolytic solution and the positive electrode is improved, and the O generated by the attack of F radicals generated from LiPF ₆ used as a solute of the electrolytic solution is reduced, whereby deterioration of the electrolytic solution is suppressed, and A long-life lithium secondary battery can be obtained.

[0017]

[Table 1]

[0018]

EFFECT OF THE INVENTION A lithium secondary battery having an improved battery life can be obtained.

Claims (1)

[Claims] 1. A lithium secondary battery comprising, as a positive electrode material, a metal chalcogen compound in which at least a part of chalcogen is fluorinated.