JPH07302587A - Nonaqueous electrolyte lithium secondary battery - Google Patents

Abstract

PURPOSE:To improve discharge performance in a discharge final stage by using a transition metal oxide alone or its mixture in a negative electrode. CONSTITUTION:A negative mix obtained by mixing anatase type titanium dioxide with lithium hydroxide, heating the mixture, then further mixing with WO3, a conductive material, and a binder is press-molded, then dried to form a negative electrode 5. Li2MNO3 is obtained by mixing manganese dioxide with lithium hydroxide, then drying the mixture is mixed with a conductive material and a binder to obtain a positive mix, and the positive mix is press-molded, then dried to form a positive electrode 4. A lithium metal sheet is pressed against a negative case 2, the negative electrode 5 is brought into contact with the lithium sheet, an electrolyte is poured, and lithium is reacted with the negative electrode 5 to store lithium in the negative electrode 5. Voltage decrease is slow until the voltage enters a lithium ion releasing potential region. Charge/ discharge cycles are stable up to 100 cycles and reversibility loss caused by using the mixture of the active material in the negative electrode 5 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte lithium secondary battery using a transition metal oxide for both positive and negative electrodes.

[0002]

2. Description of the Related Art Numerous substances such as vanadium pentoxide, manganese oxide, spinel-type manganese oxide, lithium cobalt oxide, and lithium nickel oxide have been investigated and used as suitable positive electrode active materials for non-aqueous electrolyte lithium secondary batteries. The discharge cycle life, voltage, and capacity have been obtained, and some have already entered the practical stage. On the other hand, as a negative electrode, lithium metal or lithium alloy is being studied. However, these metals do not always have sufficient charge / discharge cycle characteristics, and there is a tendency that the battery life is significantly shortened by the deposition of lithium dendride on the negative electrode or by the miniaturization. In order to solve this problem, a carbon negative electrode capable of inserting and extracting lithium has been developed, and the charge / discharge cycle characteristics of the battery have been significantly improved. Also,
Japanese Patent Laid-Open No. 63-114064 discloses that the charge / discharge cycle characteristics of a battery are stabilized for a long period of time by using a transition metal oxide for the negative electrode. Further, as one of the attempts, a battery using a spinel type lithium-titanium oxide as a negative electrode active material has been reported. Since spinel-type lithium-titanium oxide shows a very flat potential of about 1.5 V with respect to lithium when lithium is released, vanadium pentoxide, manganese oxide, spinel-type manganese oxide, lithium cobalt oxide, and A lithium secondary battery having a voltage of about 1.5 V or 2.0 V can be obtained by combining with any one of lithium nickel oxides.

On the other hand, recent electronic devices using a small secondary battery have a type having an alarm function for displaying the remaining capacity of the power battery at the end of discharge, but most of them measure the capacity by detecting the battery voltage. is doing.

[0004]

However, the spinel type lithium-titanium oxide has the characteristic of showing a rapid potential change at the end of the lithium discharge, and the lithium secondary battery using this as a negative electrode is Showed a sharp voltage drop. For this reason, when the lithium secondary battery is used in an electronic device that measures the remaining capacity of the power supply battery by detecting the battery voltage, a rapid voltage drop occurs at the end of battery discharge. It was difficult to detect.

The present invention is intended to solve such a problem, and improves the discharge characteristics in the final stage of discharge by improving the flatness of the discharge curve of a lithium secondary battery using a spinel type lithium-titanium oxide as a negative electrode. In addition, the present invention provides a lithium secondary battery that facilitates detection of the battery remaining capacity of electronic devices and has excellent charge / discharge cycle characteristics.

[0006]

In order to solve the above-mentioned problems, the non-aqueous electrolyte lithium secondary battery of the present invention has WO ₃ , L for a negative electrode of spinel type lithium-titanium oxide.
One of iWO _{2 and} Nb ₂ O ₅ or a mixture of two or more thereof is used as a negative electrode active material.

[0007]

The spinel type lithium-titanium oxide can be obtained by heat treating a lithium compound and titanium oxide at 800 to 1100 ° C. This shows a relatively low and flat potential change of around 1.5 V with respect to lithium in the middle stage of lithium ion release, but shows a sharp potential rise at the end stage of lithium ion release. Therefore, when a lithium secondary battery is constructed by using spinel type lithium-titanium oxide for the negative electrode, it is possible to realize a lithium secondary battery having high energy density and excellent charge / discharge cycle characteristics. In, the battery voltage drops sharply, and it becomes difficult to detect the battery remaining capacity from the voltage change when incorporated in an electronic device.

On the other hand, transition metal oxides such as LiWO ₂ , Nb ₂ O ₅ and WO ₃ have a flat portion having a small potential change around 1.7 to 2.1 V on the basis of lithium when releasing lithium ions. It has a capacitance of 20 to 100 mAh / g. Therefore, spinel type lithium-
When a lithium secondary battery is constructed by using a mixture of titanium oxide and the above oxide as a negative electrode active material, a discharge curve with a high sustaining voltage is obtained at the start of discharge by taking advantage of the characteristics of spinel type lithium-titanium oxide. In addition, in the final stage of discharge, a gradually decreasing discharge curve that takes advantage of the characteristics of the transition metal oxides of LiWO ₂ , Nb ₂ O ₅ , and WO ₃ is obtained. Then, by using this negative electrode, it is possible to obtain a lithium secondary battery having a high energy density and in which the battery residual capacity can be easily recognized by detecting the battery voltage at the end of discharge. On the other hand, as the positive electrode active material, vanadium pentoxide, manganese oxide, spinel-type manganese oxide, lithium cobalt oxide, lithium nickel oxide, or the like can be used. In addition, as the electrolyte, propylene carbonate (PC), ethylene carbonate (E
C), butylene carbonate (BC) and other high viscosity solvents, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), diethyl carbonate (DE)
In a mixed solvent in which C) and the like are mixed, as a solute, LiCl
O ₄ , LiBF ₄ , LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ ,
LiCF ₃ SO ₃ or the like can be dissolved and used.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

Spinel type lithium-titanium oxide is
Titanium dioxide and lithium hydroxide 5: 4 atom
After mixing in the ratio, add in air at 900 ℃ for 15 hours.
Obtained by heat treatment. This and WO₃, With conductive agent
Carbon black and fluorocarbon resin as a binder
Mix the dispersion at a weight ratio of 60: 30: 5: 5.
As a negative electrode mixture. This negative electrode mixture is 2 ton / cm²Direct
After pressure molding into pellets with a diameter of 16 mm, water content is 1% or less
In a dry atmosphere at 250 ° C for 24 hours
This was used as the negative electrode. The positive electrode active material is manganese dioxide
In the air after mixing lithium hydroxide in a molar ratio of 1: 2
Heat treatment at 400 ° C for 15 hours at Li ₂MnO₃Got
It was The active material powder thus obtained, and the conductive agent
Carbon black, fluororesin dispa as binder
Of the positive electrode mixture by mixing the mixture in a weight ratio of 90: 5: 5.
did. This positive electrode mixture is 2 ton / cm²With a diameter of 16 mm
In a dry atmosphere with a water content of 1% or less after pressure molding
Dry in air at 250 ° C for 24 hours and
It was a pole. In addition, the electrolyte contains propylene carbonate
Li as a solute in a mixed solvent of 1,2-dimethoxyethane
N (CF₃SO₂)₂1mol / l dissolved in
I was there. Assembled in FIG. 1 using the above positive electrode, negative electrode and electrolyte
The cross section of the coin type lithium secondary battery which was erected is shown. 1,
2 is a positive and negative case made of stainless steel. 3 is poly
Insulating packing made of propylene. 4 is a positive electrode
It 5 is a negative electrode, a lithium metal sheet is a negative electrode case
In advance, and after contacting the negative electrode to this,
Inject electrolyte to react lithium with negative electrode
The negative electrode is used for storage. 6 is polypropy
It is a separator made of ren. in this way
The battery thus obtained is referred to as Battery A of the present invention.

Next, WO ₃ and lithium hydroxide were mixed at a molar ratio of 1: 1 and then heat-treated in air at 400 ° C. for 15 hours to obtain LiWO ₂ powder. And, the spinel type lithium-titanium oxide and LiW
O _2, carbon black as a conductive agent, a fluorine resin dispersion as a binder 60: 30: 5: was mixed in a weight ratio of 5 anode mixture. 2t of this negative electrode mixture
After pressure-molding into a pellet having a diameter of 16 mm at a pressure of on / cm ² , the pellet was dried at 250 ° C. for 24 hours in a dry atmosphere having a water content of 1% or less, to obtain a negative electrode. A coin-type lithium secondary battery similar to that of the present invention was prepared except that this negative electrode was used, and the battery thus obtained was designated as Battery B of the present invention.

Then, niobium hydroxide Nb (OH) ₅ was added to 900
Heat treatment was performed at 6 ° C. for 6 hours to obtain H-type Nb ₂ O ₅ powder.
Then, the spinel type lithium-titanium oxide and Li
WO ₂ ; carbon black as a conductive agent; fluororesin dispersion as a binder, 60: 30: 5: 5
To prepare a negative electrode mixture. This negative electrode mixture is 2
After pressure molding to a pellet having a diameter of 16 mm at ton / cm ² , the pellet was dried at 250 ° C. for 24 hours in a dry atmosphere having a water content of 1% or less to obtain a negative electrode. A coin-type lithium secondary battery similar to that of the present invention was produced except that this negative electrode was used, and the battery thus obtained was designated as Battery C of the present invention.

For comparison, the spinel type lithium-titanium oxide is used for the negative electrode, carbon black is used as the conductive agent, and fluororesin dispersion is used as the binder.
A battery similar to that of the present invention was prepared except that the mixture was carried out at a weight ratio of 0: 5: 5, and this was used as a comparative battery D.

Next, using the above batteries A, B, C and D,
After performing constant voltage charging at 2.0 V, discharging was performed at a constant current of 2 mA. The discharge curve of each battery at this time is shown in FIG.

As is apparent from FIG. 2, in Comparative Battery D in which the negative electrode active material was only spinel type lithium-titanium oxide, the battery voltage dropped sharply at the end of discharge, whereas in Battery A of the present invention. , B, and C, the battery voltage at the end of discharge gradually inclines from around 1.2V to around 0.8V. This is because when the battery voltage of the battery of the present invention was 1.2 V, WO ₃ and LiW were obtained, respectively.
This is because the emission potential region of lithium ions of O ₂ and Nb ₂ O ₅ is entered.

Next, in FIG. 3, 2.4 mA is applied at a constant current of 2 mA.
It shows a change in discharge capacity of each battery obtained when charging and discharging between V and 1.0V. All the batteries remained stable up to 100 cycles, and reversibility was not lost by using the mixture of the active materials for the negative electrode. Further, WO ₃ , LiWO ₂ , and Nb ₂ O ₅ were mixed in a combination of two or more kinds and the same evaluation was performed, but the effect was exactly the same. Further, as a positive electrode, vanadium pentoxide,
The same evaluation was performed using manganese oxide, spinel-type manganese oxide, lithium cobalt oxide, and lithium nickel oxide, but the effect was exactly the same.

[0017]

As is evident from the foregoing description, a lithium secondary battery of the present invention, the spinel-type lithium - WO ₃ with respect to the negative electrode in a lithium secondary battery using titanium oxide in the negative electrode, Li
One of WO _2, Nb ₂ O _5, or by mixing these mixtures can improve the discharge characteristics of the discharge end.

Therefore, it is possible to easily detect the battery remaining capacity from the voltage change at the end of discharge.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a lithium secondary battery of the present invention.

FIG. 2 is a discharge characteristic diagram of a battery of the present invention and a comparative battery.

FIG. 3 is a charge / discharge cycle characteristic diagram of a battery of the present invention and a comparative battery.

[Explanation of symbols]

 1 Positive Case 2 Negative Case 3 Insulating Packing 4 Positive 5 Negative 6 Separator

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Nobuharu Koshiba 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolytic solution, wherein a mixture of spinel type lithium-titanium oxide and tungsten oxide is used for the negative electrode. 2. The non-aqueous electrolyte lithium secondary battery according to claim 1, wherein the tungsten oxide is WO ₃ . 3. The non-aqueous electrolyte lithium secondary battery according to claim 1, wherein the tungsten oxide is LiWO ₂ . 4. A lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the negative electrode uses a mixture of spinel type lithium-titanium oxide and Nb ₂ O ₅ for the non-aqueous electrolyte lithium secondary battery.