JPH10188977A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery having excellent cycle characteristic and rate characteristics by using LiVTiO4 as an active material for a positive electrode or negative electrode. SOLUTION: LiVTiO4 has the cubic crystal structure of spinel structure, and in the case where it is used as a positive electrode active material, lithium is inserted into a crystal by discharging, and lithium is drawn from the crystal by charging. In the case where LiVTiO4 is used as a negative electrode active material, lithium is inserted into a crystal by charge, and lithium is drawn from the crystal by discharge. An electrode having LiVTiO4 as the active material can be manufactured by mixing a conductive agent and binder agent with LiVTiO4 in an ordinary way and pressure-molding them. As a conductive agent, a carbon material is sued in usual. Preferably, carbon black such as graphite and acetylene black is used. As a binder agent, fluororesin is used in usual. Preferably, polytetrafluoroethylene and polyvinylidene fluoride is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery provided with an improved positive electrode or negative electrode and having excellent cycle characteristics and rate characteristics.

[0002]

2. Description of the Related Art Lithium secondary batteries are known. This one
Is, for example, LiCoO_TwoAnd LiNi _1-xCo_xO_Two,
LiNiO_Two, LiMn_TwoO_Four, LiMnO_TwoRepresented by etc.
Positive electrode with the material to be used as the positive electrode active material, lithium metal,
Lithium alloy or a substance that absorbs and releases lithium
A negative electrode as an active material is provided. Lithium rechargeable batteries are
High pressure and large charge / discharge capacity
Has been sent.

[0003]

However, the conventional lithium secondary battery has a problem that its capacity is apt to decrease when charge and discharge are repeated, that is, the cycle characteristics are not good. In addition, there is a need to improve the charge / discharge current density dependence of the charge / discharge capacity, that is, the rate characteristics. Accordingly, an object of the present invention is to provide a lithium secondary battery having excellent cycle characteristics and rate characteristics.

[0004]

According to the present invention, LiV
By using a positive electrode or a negative electrode containing a composite oxide represented by TiO ₄ as an active material, cycle characteristics and rate characteristics of a lithium secondary battery can be improved.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail.
The lithium-vanadium-titanium composite oxide represented by VTiO ₄ is known, but has not been known to be used as an active material of a lithium secondary battery. LiV
TiO ₄ has a cubic crystal structure having a spinel structure. When used as a positive electrode active material, lithium is inserted into the crystal by discharging, and lithium is extracted from the crystal by charging. Conversely, when used as a negative electrode active material, lithium is inserted into the crystal by charging, and lithium is extracted from the crystal by discharging. The production of LiVTiO ₄ may be carried out by a known method. For example, titanium dioxide (TiO ₂ ) and LiVO ₂ are mixed at a ratio of 1: 1 (molar ratio), and calcined at 600 to 800 ° C. for 10 to 48 hours. It can be easily manufactured.

[0006] LiVTiO_FourAn electrode using the active material
To do, LiVTiO_FourConductive agent and binder in the usual way
And pressure molding. Electricity as conductive agent
Those that are chemically stable and have high conductivity without being attacked by the electrolyte are preferred.
Preferably, a carbon material is usually used. Preferably graphite
And carbon black such as acetylene black
It is. The binder is also electrochemically stable and eroded by the electrolyte
Is not preferred, usually a fluororesin is used
You. Preferably polytetrafluoroethylene or polyvinyl alcohol
Redenfluoride is used. When creating electrodes
LiVTiO _Four, Conductive agent and binder mixing ratio (weight
The amount of the conductive agent is usually 10 to 10
30, the binder is 3 to 10, the balance is LiVTiO_FourTo be
Is appropriate.

The lithium secondary battery according to the present invention can be manufactured by a conventional method except that the above-mentioned electrode using LiVTiO ₄ as an active material is used for a positive electrode or a negative electrode. For example, as a counter electrode of an electrode using LiVTiO ₄ as an active material, various types known as a positive electrode or a negative electrode of a lithium secondary battery can be used. Although various known separators can be used for the separator separating the positive electrode and the negative electrode, it is usually preferable to use a porous polyolefin film, particularly a porous polypropylene film. A known electrolyte in which a lithium salt is dissolved in a non-aqueous solvent can be used as the electrolyte.

[0008]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples. Production of LiVTiO ₄ : Lithium carbonate and vanadium pentoxide were mixed well in an equimolar ratio. This mixture was heated at 500 ° C. for 6 hours in a hydrogen stream, and further heated at 700 ° C. for 10 hours in a hydrogen stream to synthesize LiVO ₂ . After mixing LiVO ₂ and titanium dioxide in an equimolar ratio, the mixture was press-molded and wrapped in platinum foil. This is vacuum-sealed in a quartz glass tube,
After heating at 0 ° C. for 24 hours, annealing at 400 ° C. for 48 hours produced LiVTiO ₄ . This LiVT
As a result of powder X-ray diffraction, iO ₄ was a cubic single phase.

Example 1 LiVTiO ₄ obtained above was pulverized, and acetylene black and polytetrafluoroethylene were added in a weight ratio of 7 to the pulverized LiVTiO _4.
The mixture was mixed to give a ratio of 5: 20: 5. This mixture 0.1
g was press-molded at a pressure of 1 ton / cm ^{2 to} a diameter of 16 mm to obtain a positive electrode. With a porous polypropylene film separator in between, the above positive electrode and negative electrode having a diameter of 1
6mm, 0.4mm thick lithium metal plate is arranged,
An electrolyte was added thereto and sealed, to produce a lithium secondary battery. As the electrolyte, propylene carbonate and 1,
A solution obtained by dissolving lithium perchlorate in an equal volume mixture with 2-dimethoxyethane so as to be 1 mol / liter was used.

Using this lithium secondary battery, a constant current charge / discharge cycle test was performed at a charge / discharge current of 2 mA and a voltage range of 1.0 V to 3.0 V. As a result, the initial discharge capacity was 146 mAh / g-LiVTiO ₄ , and the ratio of the discharge capacity at the 200th cycle to the initial discharge capacity was 89.
It was 0%. FIG. 1 shows a charge / discharge voltage curve of this lithium secondary battery. From this figure, it can be seen that this battery exhibits a flat voltage of about 1.7V. FIG. 2 shows the rate characteristics of this battery.

Example 2 LiVTiO obtained above_FourCrush the acetylene
Black and polytetrafluoroethylene in a weight ratio of 7
The mixture was mixed to give a ratio of 5: 20: 5. This mixture 0.1
g is 1 ton / cm^TwoPress to 16mm in diameter
It was molded and used as a negative electrode. LiCoO_TwoAnd acetylene bra
And polytetrafluoroethylene in a weight ratio of 75:
0.125 g mixed to give 20: 5 is 1 t
on / cm ^TwoPress molding to a diameter of 16mm with pressure of
Pole. Porous polypropylene film separator
The positive electrode and the negative electrode are arranged with the electrode interposed therebetween.
Add the same electrolyte solution as used in Step 2 and seal it.
A battery was manufactured.

Using this lithium secondary battery, a constant current charge / discharge cycle test was performed at a charge / discharge current of 2 mA and a voltage range of 1.0 V to 3.3 V. As a result, the initial discharge capacity was 140 mAh / g-LiVTiO ₄ , and the ratio of the discharge capacity at the 200th cycle to the initial discharge capacity was 87.
2%. FIG. 3 shows a charge / discharge voltage curve of this lithium secondary battery. From this figure, it can be seen that this battery shows a flat voltage of about 2.3V.

[Brief description of the drawings]

FIG. 1 is a charge / discharge voltage curve of a lithium secondary battery including a positive electrode using LiVTiO ₄ as a positive electrode active material and a negative electrode of lithium metal.

FIG. 2 is a diagram showing rate characteristics of the battery of FIG.

FIG. 3 shows a negative electrode using LiVTiO ₄ as a negative electrode active material;
9 is a charge / discharge voltage curve of a lithium secondary battery including a positive electrode using iCoO ₂ as a positive electrode active material.

Claims (2)

[Claims] 1. A lithium secondary battery comprising a positive electrode using a composite oxide represented by LiVTiO ₄ as a positive electrode active material. 2. A lithium secondary battery comprising a negative electrode using a composite oxide represented by LiVTiO ₄ as a negative electrode active material.