JP3077508B2 - Non-aqueous electrolyte lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte lithium secondary battery in which both positive and negative electrodes use a transition metal oxide.

[0002]

2. Description of the Related Art Numerous substances such as vanadium pentoxide, manganese oxide, spinel-type manganese oxide, lithium cobaltate, and lithium nickelate have been studied as positive electrode active materials for nonaqueous 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, lithium metal and lithium alloy are being studied as the negative electrode. However, these metals do not always have sufficient charge / discharge cycle characteristics, and the dendrites of lithium are deposited on the negative electrode or are miniaturized, so that the battery life tends to be significantly shortened. In order to solve this problem, a carbon anode capable of inserting and extracting lithium has been developed, and the charge / discharge cycle characteristics of the battery have been greatly improved. Also,
JP-A-63-114064 discloses that the use of a transition metal oxide for the negative electrode stabilizes the charge / discharge cycle characteristics of the battery for a long period of time. Further, as one of such attempts, a battery using a spinel-type lithium-titanium oxide as a negative electrode active material has been reported. The spinel-type lithium-titanium oxide exhibits a very flat potential of about 1.5 V on the basis of lithium when lithium is released. Therefore, vanadium pentoxide, manganese oxide, spinel-type manganese oxide, lithium cobalt oxide, By combining with any one of lithium nickel oxide, a lithium secondary battery having a voltage of about 1.5 V or about 2.0 V can be obtained.

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

[0004]

However, the spinel-type lithium-titanium oxide has a characteristic that shows a sudden change in potential at the end of release of lithium. 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 sharp voltage drop occurs at the end of battery discharge. It was difficult to detect.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and improves the flatness of the discharge curve of a lithium secondary battery using a spinel type lithium-titanium oxide as a negative electrode to improve the discharge characteristics at the end of discharge. It is another object of the present invention to provide a lithium secondary battery that facilitates detection of the remaining battery capacity of an electronic device and has excellent charge / discharge cycle characteristics.

[0006]

Means for Solving the Problems In order to solve the above problems, a nonaqueous electrolyte lithium secondary battery of the present invention comprises a Li-based battery.
The negative electrode of titanium oxide, spinel type lithium - - spinel-type lithium having a discharge potential near 1.5V quasi titanium
Any one of WO ₃ , LiWO _2, or Nb ₂ O ₅ having a higher discharge potential than an oxide, 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 indicates 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 rise in potential at the end of lithium ion release. Therefore, when a lithium secondary battery is configured using a spinel-type lithium-titanium oxide for the negative electrode, a lithium secondary battery having a high energy density and excellent charge-discharge cycle characteristics can be realized. In, the battery voltage drops rapidly, and it is difficult to detect the remaining battery capacity from the voltage change when the battery is incorporated in an electronic device.

On the other hand, transition metal oxides such as LiWO ₂ , Nb ₂ O ₅ and WO ₃ form a flat portion having a small potential change at about 1.7 to 2.1 V on the basis of lithium when lithium ions are released. It has an electric capacity of 20 to 100 mAh / g. Therefore, spinel lithium
If a lithium secondary battery is formed using a mixture of titanium oxide and the above oxide as a negative electrode active material, a discharge curve with a high sustaining voltage can be obtained at the start of discharge, taking advantage of the characteristics of the spinel lithium-titanium oxide. Further, at the end of discharge, a gently falling discharge curve utilizing the characteristics of transition metal oxides of LiWO ₂ , Nb ₂ O ₅ and WO ₃ is obtained. By using this negative electrode, a lithium secondary battery having a high energy density and easily recognizing the remaining battery capacity by detecting the battery voltage at the end of discharging can be obtained. On the other hand, as the positive electrode active material, vanadium pentoxide, manganese oxide, spinel-type manganese oxide, lithium cobaltate, lithium nickelate, or the like can be used. As the electrolyte, propylene carbonate (PC), ethylene carbonate (E
C), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), diethyl carbonate (DE) in a high-viscosity solvent such as butylene carbonate (BC).
C) as a solute in a mixed solvent containing
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.

[0010] The spinel type lithium-titanium oxide is an analog.
5: 4 atoms of titanium dioxide and lithium hydroxide
After mixing at the same ratio, heat in air at 900 ° C for 15 hours.
Obtained by heat treatment. This and WO_Three, Conductive agent and
Carbon black and fluorocarbon resin as binder
Mix the dispersion in a weight ratio of 60: 30: 5: 5
To form a negative electrode mixture. This negative electrode mixture is 2 ton / cm^TwoDirectly
Moisture less than 1% after pressure molding into 16mm diameter pellet
In a dry atmosphere at 250 ° C for 24 hours.
This was used as a negative electrode. The positive electrode active material is manganese dioxide.
After mixing lithium hydroxide in a molar ratio of 1: 2,
Heat treatment at 400 ° C for 15 hours with Li _TwoMnO_ThreeGet
Was. The active material powder thus obtained is used as a conductive agent.
Carbon black, fluororesin disperser as binder
And the positive electrode mixture was mixed at a weight ratio of 90: 5: 5.
did. This positive electrode mixture is 2 ton / cm^TwoWith a 16mm diameter pen
After pressure molding into a ret, dry atmosphere with moisture of 1% or less
Dry in the air at 250 ° C. for 24 hours,
Pole. In addition, propylene carbonate is used as the electrolyte.
Li as a solute in a mixed solvent of 1,2-dimethoxyethane
N (CF_ThreeSO_Two)_Two1mol / l dissolved
Was. FIG. 1 shows an assembly using the above positive electrode, negative electrode, and electrolyte solution.
FIG. 1 shows a cross-sectional view of an upright coin-type lithium secondary battery. 1,
Reference numeral 2 denotes positive and negative electrode cases made of stainless steel. 3 is poly
It is an insulating packing made of propylene. 4 is a positive electrode
You. Reference numeral 5 denotes a negative electrode, and a lithium metal sheet is a negative electrode case.
To the negative electrode in advance,
Inject electrolyte to allow lithium to react with negative electrode
Is stored in the negative electrode. 6 is polypropylene
This is a separator made of a non-woven fabric 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. Then, the spinel-type lithium-titanium oxide and LiW
O ₂ , carbon black as a conductive agent, and a fluororesin dispersion as a binder were mixed at a weight ratio of 60: 30: 5: 5 to prepare a negative electrode mixture. 2t of this negative electrode mixture
After being formed 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 was produced in the same manner as in the present invention except that this negative electrode was used, and the battery thus obtained was designated as Battery B of the present invention.

Next, 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, a fluorine resin dispersion as a binder 60: 30: 5: 5
To obtain a negative electrode mixture. This negative electrode mixture is
After being pressed into 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 the present invention was produced except that this negative electrode was used, and the battery thus obtained was used as Battery C of the present invention.

For comparison, the negative electrode was made of the spinel-type lithium-titanium oxide, carbon black as a conductive agent, and fluororesin dispersion as a binder.
A battery similar to the present invention was prepared except that the mixture was mixed at a weight ratio of 0: 5: 5, and this was designated as Comparative Battery D.

Next, using the batteries A, B, C, and D,
After charging at a constant voltage of 2.0 V, the battery was discharged at a constant current of 2 mA. FIG. 2 shows a discharge curve of each battery at this time.

As is apparent from FIG. 2, in the battery D of the comparative example in which the negative electrode active material was only the spinel type lithium-titanium oxide, the battery voltage dropped sharply at the end of discharge, whereas the battery A of the present invention was used. , B and C all have a gradual slope of the battery voltage at the end of discharge from around 1.2 V to around 0.8 V. This is because when the battery voltage of the battery of the present invention reaches 1.2 V, WO ₃ and LiW
This is because it enters the emission potential region of lithium ions of O ₂ and Nb ₂ O ₅ .

FIG. 3 shows a constant current of 2 mA at 2.4.
It shows a change in the discharge capacity of each battery obtained when charging and discharging between V and 1.0V. All of the batteries are stable up to 100 cycles, and the reversibility is not lost by using the active material mixture 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 completely the same. Further, as a positive electrode, vanadium pentoxide,
The same evaluation was performed using manganese oxide, spinel-type manganese oxide, lithium cobaltate, and lithium nickelate, but the effects were completely the same.

[0017]

As described above, according to the lithium secondary battery of the present invention, in the lithium secondary battery using the spinel type lithium-titanium oxide for the negative electrode, WO ₃ and Li
By mixing any of WO ₂ , Nb ₂ O ₅ , or a mixture thereof, the discharge characteristics at the end of discharge can be improved.

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

[Brief description of the drawings]

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

FIG. 2 is a discharge characteristic diagram of a battery in comparison with the present invention.

FIG. 3 is a diagram showing charge / discharge cycle characteristics of a battery in comparison with the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode case 2 Negative electrode case 3 Insulating packing 4 Positive electrode 5 Negative electrode 6 Separator

──────────────────────────────────────────────────続 き Continuation of the front page (72) Nobuharu Koshiba, Inventor 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-6-318458 (JP, A) JP-A-5- 299089 (JP, A) JP-A-6-60867 (JP, A) JP-A-6-215770 (JP, A) JP-A-6-310143 (JP, A) JP-A-6-318457 (JP, A) JP-A-6-333569 (JP, A) JP-A-7-14580 (JP, A) JP-A-7-14581 (JP, A) JP-A-7-29604 (JP, A) JP-A-7-29606 (JP, A) JP-A-7-29607 (JP, A) JP-A-7-85878 (JP, A) JP-A-7-122298 (JP, A) JP-A-7-161348 (JP, A) JP-A-7-235291 (JP, A) JP-A-7-288124 (JP, A) The Chemical Society of Japan [Fundamentals] revised third edition (58) investigated the field (Int.Cl. ^7, DB name) H01M 4/02 H01M 4/58 H01M 10/40

Claims (4)

(57) [Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the negative electrode has a voltage of about 1.5 V on the basis of Li.
And a discharge potential higher than the spinel lithium-titanium oxide.
A non-aqueous electrolyte lithium secondary battery comprising a mixture of a tungsten oxide having an electric potential . 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 has a voltage of about 1.5 V on the basis of Li.
And a discharge potential higher than the spinel lithium-titanium oxide.
A non-aqueous electrolyte lithium secondary battery comprising a mixture of Nb ₂ O ₅ having an electric potential.