JPH1027609A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

[PROBLEMS] To improve charge / discharge cycle characteristics and storage characteristics. SOLUTION: A negative electrode 5 is made of lithium or a lithium alloy or a lithium-titanium oxide having a spinel structure.
The positive electrode 4 is made of an active material containing a lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ having a spinel structure, and the electrolyte is LiN (CF ₃ S
O ₂ ) ₂ , and a mixed solvent of two or more components containing ethylene carbonate as a solvent is used.

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 secondary battery used as a main power supply and a backup power supply for electronic equipment,
In particular, it relates to a non-aqueous electrolyte lithium secondary battery.

[0002]

2. Description of the Related Art In general, non-aqueous electrolyte batteries have a high energy density, can be made smaller and lighter, and have excellent storage characteristics and leakage resistance. Although the demand as a power source for memory backup is increasing year by year, primary batteries which cannot charge such batteries are mainly used. However, with the remarkable development of portable electronic devices in recent years, there has been a strong demand for secondary batteries that take advantage of the characteristics of nonaqueous electrolyte batteries from the viewpoints of further miniaturization, economy, and maintenance-free equipment. I have.
For this reason, non-aqueous electrolyte secondary batteries have been actively proposed and developed, and some have been put to practical use and commercialized, but there is still room for improvement.

As a material for a negative electrode of a conventional nonaqueous electrolyte secondary battery, lithium metal or a lithium alloy of lithium and lead or aluminum has been studied.
Later, carbon anodes doped with lithium appeared, and the charge / discharge cycle characteristics were greatly improved. Also,
It has been proposed to stabilize charge / discharge cycle characteristics over a long period of time by using a transition metal oxide for the negative electrode (see, for example, JP-A-2-49364).

On the other hand, as the material of the positive electrode, V ₂ O ₅ , Nb
₂ O ₅ , MnO ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂
Materials that allow lithium ions to enter and leave between layers of metal oxide crystals such as O ₄ and between lattice positions or lattice gaps have been widely studied, and appropriate charge / discharge cycle life, voltage, and capacity have been obtained. Some are.

[0005]

In the conventional positive electrode material of a non-aqueous electrolyte secondary battery, LiCoO ₂ is difficult to obtain in a stable and continuous manner from the viewpoint of a long term. In addition, LiNiO ₂ needs to mix a binder and a conductive agent, and this mixing process must be performed in a non-aqueous environment, and there is a problem that handling is complicated.

[0006] The battery characteristics are greatly affected by the type of electrolyte used. Generally, when manganese oxide is used for the positive electrode, the positive electrode side becomes an oxidizing atmosphere during charging, and depending on the charging voltage, the manganese oxide is decomposed by oxidation of the electrolytic solution. May act as a catalyst for the reaction. At that time, intense gas generation and manganese ion elution into the electrolyte occur,
As a result, there is a problem that the battery characteristics are rapidly deteriorated. This action is achieved by using LiCF ₃ SO ₃ ,
It becomes remarkable when LiBF ₄ is used.

[0007]

In order to solve the above problems, a non-aqueous electrolyte secondary battery according to the present invention comprises lithium or a lithium alloy or a lithium-titanium oxide having a spinel structure. Is used as an active material of a negative electrode, and a spinel-type lithium-manganese oxide Li _4/3 Mn _5/3 O ₄
The active material containing is used as the positive electrode.

The charge and discharge cycle characteristics are improved by using an active material containing a lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ having a spinel-type structure which is easy to synthesize and handle and is inexpensive for the positive electrode. And excellent storage characteristics.

It is to be noted that lithium perfluoromethylsulfonylimide (LiN (C
By using F ₃ SO ₂ ) ₂ ) and using a mixed solvent of at least a two-component system containing ethylene carbonate (EC), which is a high-viscosity solvent, as a solvent, the battery characteristics can be further improved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, lithium or a lithium alloy is used as an active material of a negative electrode, and an active material containing a lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ having a spinel structure is used as a positive electrode. Things.

Further, a lithium-titanium oxide having a spinel structure is used as an active material of a negative electrode, and an active material containing a lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ having a spinel structure is used as a positive electrode. It is.

Also, lithium-titanium having a spinel structure
As the oxide, Li_4/3Ti_5/3O _Four, LiTi_TwoO_FourTo
Can be used.

Furthermore, lithium perfluoromethylsulfonylimide (LiN (CF
It is effective to use ₃ SO ₂ ) ₂ ) and to use a mixed solvent of at least a two-component system containing ethylene carbonate (EC) which is a high-viscosity solvent as a solvent.

Lithium having a spinel structure used for a positive electrode
Manganese oxide Li _4/3 Mn _5/3 O ₄ is obtained from Moniq
e. N. Richard, E .; W. Fuller, J .;
R. Dahn, Solid State Ionics
73 (1994) 81-91, it can be obtained by heat-treating a mixture of manganese oxyhydroxide (γ-MnOOH) and a lithium salt, and has a voltage of 3V class based on lithium. However, a capacity of 0.3 to 1.0 electrons per mole can be obtained, the reversibility of charge / discharge is excellent, and it can be manufactured at low cost.

Further, among lithium alloys used for the negative electrode,
Lithium-aluminum alloy is 0.2 ~
By having a voltage of 0.5 V and combining with the positive electrode using Li _4/3 Mn _5/3 O ₄ , a voltage of about 2.5 V can be developed.

The spinel type lithium-titanium oxide (hereinafter abbreviated as titanium spinel) used for the negative electrode is Li
It is represented by _{1 + x} Ti _2-x O ₄ (x = −0.2 to 1/3), and typical examples include Li _4/3 Ti _5/3 O ₄ and LiTi ₂ O ₄ . This titanium spinel has a voltage of about 1.5 V based on lithium, and can theoretically obtain a capacity of one electron per mole. Therefore, this Li _4/3 Mn _5/3 O
By combining the positive electrode using No. ₄ with the negative electrode using titanium spinel, a voltage of about 1.5 V can be developed.

The conditions for synthesizing the lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ having a spinel structure are not limited to manganese oxyhydroxide as a raw material, but may be gamma manganese dioxide (γ-manganese dioxide). It can also be synthesized using MnO ₂ ), trimanganese tetroxide (Mn ₃ O ₄ ), or the like.

As the electrolytic solution, 1,2-2-butane is used in a high-viscosity solvent such as propylene carbonate (PC), ethylene carbonate (EC) and butylene carbonate (BC).
A mixture of a low-viscosity solvent such as dimethoxyethane (DME), 1,2-diethoxyethane (DEE) and diethyl carbonate (DEC) is mixed with LiC as an electrolyte.
10 ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiPF ₆ , Li
N (CF ₃ SO ₂ ) ₂ or the like can be dissolved and used.

The battery characteristics include storage characteristics, overcharge resistance characteristics, overdischarge resistance characteristics, etc. in addition to charge / discharge characteristics, and it is necessary to select an electrolyte in consideration of these characteristics. When emphasis is placed on storage characteristics, L
It was confirmed that the use of a mixed system containing iN (CF ₃ SO ₂ ) ₂ and ethylene carbonate (EC) as a solvent was effective.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

Example 1 After mixing manganese oxyhydroxide and lithium hydroxide in a molar ratio of 5: 4, the mixture was heated in air at 450 ° C. for 8 hours to obtain Li.
_4/3 Mn _5/3 O ₄ is obtained. Li _4/3 Mn thus obtained
_5/3 O ₄ was used as an active material powder, carbon black was used as a conductive agent, a fluororesin dispersion was used as a binder, and the active material powder, the conductive agent, and the binder were 88: 6: 6 as solids. The mixture was mixed at a weight ratio of 2 to form a positive electrode mixture. The positive electrode mixture was pressed into pellets having a diameter of 16 mm at ² ton / cm ² and then dried at 250 ° C. for 24 hours in a dry atmosphere having a moisture content of 1% or less. This was used as a positive electrode.

Anatase type titanium dioxide and lithium hydroxide
And a 5: 4 molar ratio, and heat at 900 ° C for 15 hours.
Calcined, Li_4/3Ti_5/3O_FourWas obtained. This Li_4/3
Ti _5/3O_FourIs used as the active material powder and carbon is used as the conductive agent.
Black, fluororesin dispurge as binder
The active material powder, conductive agent, and binder are solidified
In a weight ratio of 85: 8: 7, and
Then, this negative electrode mixture is 2 ton / cm^TwoWith a diameter of 16mm
After pressure molding into pellets, dry atmosphere with moisture of 1% or less
It was dried at 250 ° C. in an atmosphere to obtain a negative electrode.

A coil assembled using the above-described positive electrode and negative electrode
Fig. 1 shows a cross-sectional view of a non-aqueous electrolyte lithium secondary battery.
1 is a stainless steel positive electrode case, 2 is stainless steel
Negative case, 3 is an insulating packing made of polypropylene resin
And 4 for Li_4/3Mn_5/3O _FourPositive electrode using as active material, 5
Is Li that has absorbed lithium_4/3Ti_5/3O_FourWith active material
Negative electrode, and the lithium metal is
Pre-compressed, Li _4/3Ti_5/3O_FourContact with
And Li naturally becomes Li when the electrolyte is injected._4/3Ti
_5/3O_FourReacts with Li_4/3Ti_5/3O_FourTo Dopi
It will be the one that was done. No. 6 is made of polypropylene resin
This is a separator made of woven fabric. Propium as the electrolyte
Lencarbonate (PC), ethylene carbonate (E
C) Mixed solvent of 1,1,2-dimethoxyethane (DME)
And LiClO_Four, LiBF_Four, LiCF _ThreeSO_Three, LiP
F₆, LiN (CF_ThreeSO_Two)_TwoEach electrolyte
Using a solution dissolved at a concentration of
B, C, D, and E. The dimensions of the battery were 20.
0 mm and a thickness of 2.0 mm.

(Embodiment 2) The same configuration as that of Embodiment 1 was adopted, and PC: EC: DME was used as an electrolytic solution in a volume ratio of
Using a solution in which LiN (CF ₃ SO ₂ ) ₂ was dissolved at a concentration of 1 mol / liter in a mixed solvent of 1: 1: 2, 1: 0: 1, 0: 1: 1, and a battery F, G and H.

(Embodiment 3) In the case of Embodiment 1, L
The i _4/3 Mn _5/3 O ₄ active material powder, the carbon black conductive agent, and the fluororesin dispersion binder were mixed at a solid content of 88: 6: 6 by weight to form a positive electrode mixture. The mixture was press-molded into pellets having a diameter of 16 mm at ² ton / cm ² and then dried at 250 ° C. for 24 hours in a dry atmosphere having a water content of 1% or less to obtain a positive electrode.

The structure of the battery is almost the same as that of FIG. 1 except that aluminum and lithium are melted and alloyed in an argon atmosphere, and the thickness of the anode 5 is reduced to 0.3 mm in the same atmosphere.
A lithium-aluminum alloy punched out to a diameter of 15 mm after being rolled into a sheet shape as described above is brought into close contact with the negative electrode case 2. The electrolyte used was exactly the same as in Example 1, and the respective electrolytes LiClO ₄ , LiBF ₄ ,
Batteries I, J, K, L, and M were made using LiCF ₃ SO ₃ , LiPF ₆ , and LiN (CF ₃ SO ₂ ) ₂ .

Next, the battery characteristics of the thirteen types of batteries A to M in Examples 1 to 3 described above will be described. The characteristics in the case of the first embodiment are as shown in FIGS. FIG. 2 shows batteries A, B, C,
The discharge characteristics at 2 mA for D and E are about 20 mAh when the voltage is from 2 V to 1 V.
Battery A using 10 ₄ , Battery D using LiPF ₆ , Li
Battery E using N (CF ₃ SO ₂ ) ₂ was good and LiBF ₄
And B using LiCF ₃ SO ₃ tend to be slightly lower. FIG. 3 shows the electric capacity of each cycle of discharge obtained when charging and discharging between 2.4 V and 1 V at a constant current of 2 mA. The battery C has a lower capacity than the initial state, but changes to 50 cycles in a low state, and the battery B deteriorates more rapidly than the initial state.

FIG. 4 shows that batteries A, D, and E having good discharge characteristics and charge / discharge cycle characteristics were stored in a high-temperature atmosphere at 60 ° C. for 20 days, and then charged at room temperature to 2.4 V at a constant current of 2 mA. The battery shows discharge characteristics when discharged to 1 V at the same current. The batteries D and E have relatively high recovery due to charging, particularly the battery E is high, and the battery A is greatly deteriorated. From this fact, those having good discharge characteristics, charge-discharge cycle characteristics and high-temperature storage characteristics are the cases where LiN (CF ₃ SO ₂ ) ₂ and LiPF ₆ are used as the electrolyte of the electrolytic solution, and in particular, LiN (CF ₃ SO _{2 2} ) is excellent when used.

Next, the characteristics of the second embodiment are as follows.
This is as shown in FIGS. FIG. 5 shows the discharge characteristics at 2 mA of the battery using each mixed solvent.
About 20 mAh is obtained from V to 1 V. Among them, batteries F and H are good, and battery G tends to be slightly low. FIG. 6 shows the electric capacity of each cycle of discharge obtained when charging and discharging between 2.4 V and 1 V at a constant current of 2 mA at −10 ° C., and the batteries F and G are stable. To 100 cycles, and the battery H stably changes to 100 cycles, but the capacity is lower than the initial period. FIG. 7 shows the discharge characteristics when the batteries F, G, and H were stored in a high-temperature atmosphere of 60 ° C. for 20 days, charged at room temperature with a constant current of 2 mA to 2.4 V, and discharged to 1 V with the same current. Is shown. Batteries F and H have relatively high recoveries due to charging, particularly battery F is high, and battery G is significantly degraded. This shows that the batteries F and H have excellent discharge characteristics, charge / discharge cycle characteristics, and high-temperature storage characteristics, and that the battery F is particularly excellent.

Next, the characteristics of the third embodiment are as follows.
This is as shown in FIGS. 8, 9, and 10. FIG. 8 shows the charge / discharge characteristics at 2 mA using each of the electrolytes. A voltage of about 25 mAh was obtained from a voltage of 3 V to 2 V, a battery I using LiClO ₄ , a battery L using LiPF _6, and a battery L, LiN (C
The battery M using F ₃ SO ₂ ) ₂ is good, and the battery J using LiBF ₄ and the battery K using LiCF ₃ SO ₃ tend to be slightly lower. FIG. 9 shows that a constant current of 2 mA changes from 3.1 V to 2.0 V.
5 shows the electric capacity of the discharge obtained in each cycle when charging / discharging between V. The batteries I, L, and M have been stably shifted up to 30 cycles, and the capacity of the battery K has been changed from the beginning. Although the battery J is low, it has been changed to 15 cycles in a low state, and the deterioration of the battery J has progressed rapidly from the initial stage.
FIG. 10 shows that batteries I, L, and M having good discharge characteristics and charge / discharge cycle characteristics were stored in a high-temperature atmosphere at 60 ° C. for 20 days, then charged at room temperature at a constant current of 2 mA to 3.1 V, and charged at the same current. It shows the discharge characteristics when discharging to 2.0V. The batteries L and M have a high recovery due to charging, particularly the battery M is high, and the battery I is greatly deteriorated. For this reason, even in this battery system, those having good discharge characteristics, charge / discharge cycle characteristics, and high-temperature storage characteristics are considered to be LiN (CF ₃ SO ₂ ) ₂ and Li
This is the case where PF ₆ is used, and in particular, LiN (CF ₃ SO ₂ ) ₂
Is excellent.

[0031]

As described above, the non-aqueous electrolyte secondary battery of the present invention uses the active material containing the lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ having the spinel structure as the positive electrode. ,
Lithium or a lithium alloy, or a lithium-titanium oxide having a spinel structure is used in the form of using as an active material of the negative electrode, and has a great industrial value.In particular, lithium perfluoromethylsulfonylimide is used as an electrolyte, When an electrolyte containing carbonate is used, the charge / discharge cycle characteristics and the high-temperature storage characteristics are excellent.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a coin-type nonaqueous electrolyte lithium secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing discharge characteristics of the nonaqueous electrolyte lithium secondary battery in Example 1 of the present invention.

FIG. 3 is a diagram showing charge / discharge cycle characteristics of the nonaqueous electrolyte lithium secondary battery.

FIG. 4 is a diagram showing discharge characteristics of the nonaqueous electrolyte lithium secondary battery.

FIG. 5 is a diagram showing discharge characteristics of a non-aqueous electrolyte lithium secondary battery in Example 2 of the present invention.

FIG. 6 is a diagram showing charge / discharge cycle characteristics of the nonaqueous electrolyte lithium secondary battery.

FIG. 7 is a diagram showing discharge characteristics of the nonaqueous electrolyte lithium secondary battery.

FIG. 8 is a diagram showing discharge characteristics of a non-aqueous electrolyte lithium secondary battery in Example 3 of the present invention.

FIG. 9 is a diagram showing charge / discharge cycle characteristics of the nonaqueous electrolyte lithium secondary battery.

FIG. 10 is a diagram showing discharge characteristics of the nonaqueous electrolyte lithium secondary battery.

[Explanation of symbols]

 4 Positive electrode 5 Negative electrode

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary using lithium or a lithium alloy as an active material of a negative electrode and an active material containing a lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ having a spinel structure as a positive electrode. battery. 2. A non-electrode comprising a spinel-type lithium-titanium oxide as an active material for a negative electrode and an active material containing a spinel-type lithium-manganese oxide Li _4/3 Mn _5/3 O ₄ as a positive electrode. Water electrolyte secondary battery. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the lithium-titanium oxide having a spinel structure is Li _4/3 Ti _5/3 O ₄ . 4. The non-aqueous electrolyte secondary battery according to claim ₂ , wherein the lithium-titanium oxide having a spinel structure is LiTi ₂ O ₄ . 5. An electrolyte for a non-aqueous electrolyte, comprising lithium perfluoromethylsulfonylimide (LiN (CF ₃ S
O _{2) 2)} using, as a solvent containing ethylene carbonate (EC) is a high-viscosity solvent, a non-aqueous electrolyte secondary according to any one of claims 1 to 4 using a mixed solvent of at least two-component battery.