JP2003173817A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with lithium manganese complex oxide contained in a positive electrode keeping an excellent high-temperature preservation characteristics without degrading charge/discharge characteristics of the battery such as cycle characteristics. <P>SOLUTION: The nonaqueous electrolyte secondary battery provided with a positive electrode containing a lithium manganese complex oxide and a negative electrode made of a matter capable of storing and discharging lithium ion, is also provided with a positive electrode active material containing a lithium manganese complex oxide and a lithium nickel cobalt complex oxide and electrolyte containing lithium salt in a nonaqueous solvent in a concentration of 0.8 to 1 M. <P>COPYRIGHT: (C)2003,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention relates to various portable machines.
It is a highly secure and usable power source for
The present invention relates to a non-aqueous electrolyte secondary battery having good discharge characteristics. [0002] 2. Description of the Related Art Mobile phones, notebook computers, camcorders
A small, large-capacity sealed battery
Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are used.
Have been. These non-aqueous electrolyte secondary batteries are
Volume capacity density and weight compared to secondary batteries using electrolyte
Large capacity density, etc., and can take out high voltage
Power supply for small equipment.
For electric assist bicycles, electric wheelchairs, electric vehicles, etc.
It is also expected for power sources. [0003] Lithium ion secondary batteries use lithium as a source.
Active material such as carbonaceous material that can be
Composite oxide of lithium and transition metal oxide
A positive electrode using an active material as the active material
Apply to side current collector and positive electrode current collector, and stack via separator
Cover the layers with exterior materials or swirl them.
The battery element is wound in a battery
Building. As a positive electrode active material of a lithium ion secondary battery,
In addition to lithium cobalt composite oxide, lithium
A manganese composite oxide is used. Manganese
It is much more abundant compared to cobalt,
Battery using lithium manganese composite oxide as positive electrode active material
Uses lithium cobalt composite oxide as the positive electrode active material.
Abnormal reactions occur due to short-circuiting of battery terminals, etc.
It has the feature that the safety is high even if it
Suitable for large batteries. [0005] However, lithium manganese composite oxides
A battery used as a positive electrode active material repeatedly charges and discharges.
Lithium ion using lithium cobalt composite oxide
When used at a high temperature of 40 ° C to 60 ° C compared to the secondary battery
Is known to be greatly deteriorated by charge and discharge cycles.
And the storage characteristics at high temperatures deteriorate.
The point is pointed out. This is the storage characteristics under high temperature
As one of the causes of deterioration of cycle characteristics
Substances such as lithium hexafluorophosphate used in the electrolyte
Reacts with moisture to produce acids such as hydrofluoric acid, which
Dissolves the gun complex oxide, adversely affecting battery characteristics
It is thought to have an effect. In order to solve such problems, Japanese Patent Laid-Open Publication No.
JP-A-11-297354 discloses manganese oxide or manganese oxide.
Positive electrode containing composite oxide of titanium and manganese
In a non-aqueous solvent containing ethylene carbonate.
At least LiBF_Four Is 2.0 mol / l to 5.0 mol
Non-aqueous electrolyte using a non-aqueous electrolyte dissolved at a concentration of / l
Secondary batteries have been proposed, but use of high-concentration lithium salts
There was a problem as a practical battery. Further, Japanese Patent Application Laid-Open No. 2000-21441 discloses
Has spinel-structured lithium manganate and is
LiPF as lithium salt in the medium₆ , LiBF_Four To 0.4
Using an electrolyte dissolved at a concentration of ~ 0.8 mol / l
Water electrolyte secondary batteries have been proposed.
The problem is that important cycle characteristics are sacrificed.
Was. [0008] SUMMARY OF THE INVENTION The present invention relates to a cycle
High-temperature storage without degrading battery charge / discharge characteristics such as durability
Lithium manganese with spinel structure for positive electrode with good characteristics
To provide a non-aqueous electrolyte secondary battery containing a composite oxide
It is an issue. [0009] SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a lithium ion battery.
Of positive electrode containing lithium manganese composite oxide and lithium ion absorption
Non-aqueous electrolyte secondary battery with negative electrode made of material that can be stored and released
The lithium manganate complex oxidation as the positive electrode active material
Contains lithium nickel cobalt composite oxide
And a lithium salt in a nonaqueous solvent at a concentration of 0.8 to 1 M.
Solution with a non-aqueous electrolyte secondary battery
Can be decided. The lithium salt is phosphorus hexafluoride.
At least one of lithium oxide and lithium tetrafluoroborate
The above non-aqueous electrolyte secondary battery containing at least one of them.
You. Lithium manganese composite oxide and lithium nickel
The mixing ratio of the Baltic composite oxide is 1: 1 to 19: 1 by mass.
The non-aqueous electrolyte secondary battery described above. [0010] BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to the use of lithium as a cathode material.
Non-aqueous electrolyte secondary batteries using manganese composite oxide
And the positive electrode material is lithium manganese composite oxide and lithium
Nickel-cobalt composite oxide and non-aqueous
The concentration of the lithium salt present as a supporting salt in the solvent,
By setting the value to 0.8 to 1M, the electric characteristics such as cycle characteristics can be reduced.
After storage at high temperature without deteriorating pond characteristics,
It was also found that pond characteristics could be improved
It is. The positive electrode material of the non-aqueous electrolyte secondary battery of the present invention
Lithium-manganese composite oxides contained include Li
_{1 + x}Mn_2-XO_FourSpinel represented by (0 <x ≦ 0.2)
Structural type lithium manganese composite oxide
And also as lithium nickel cobalt composite oxide
Is lithium nickel cobaltate (LiNi_1-xCo_xO
_Two ). [0012] Lithium nickel cobaltate is lithium
Suppresses elution of manganese from manganese composite oxide
Lithium manganese composite oxidation
It has a charge / discharge capacity equal to or greater than that of
It also leads to an increase in the charge / discharge capacity of the pond. [0013] Lithium manganese composite oxide and nickel
The mixing ratio with lithium baltoate is 1: 1 to 1 by mass.
It is preferably 9: 1. Occupies in both composite oxides
The amount of lithium nickel cobaltate is 5% by mass or more.
By the lithium manganese composite oxide manganese
Can be obtained, but the mixing ratio is 50%
Above, the characteristics of lithium manganese composite oxide
Safety effect is relatively reduced, lithium manganese
The same battery protection circuit as when no composite oxide is used is required.
It is not preferable because it is necessary. Also preferably, nickel
The amount of lithium cobaltate is 10 to 40% by mass.
And more preferably 15 to 30% by mass. Further, the present invention is applied to a non-aqueous electrolyte secondary battery of the present invention.
The non-aqueous electrolyte to be used is LiPF as an electrolyte.₆ Using
Preferably, the concentration in the electrolyte is 0.8 to 1M.
More preferably, the concentration of the lithium salt is
0.8-0.95M. More preferably, 0.9 to
0.95M. As a lithium salt, LiPF₆ To
In addition, LiBF_Four Using a mixture of lithium salts such as
Can be The mixing ratio is as follows:
20% by mass or less can be mixed. When the concentration of the lithium salt is less than 0.8M
When the temperature rises, the rate characteristics after high temperature storage, that is, the discharge load characteristics
And the lithium salt concentration is greater than 1M
The impedance change after storage at high temperature becomes large
It is not preferred. Further, the non-aqueous electrolyte used in the present invention
Are ethylene carbonate and propylene as non-aqueous solvents.
Carbonate, dimethyl carbonate, diethyl carbonate
Carbonate, methyl ethyl carbonate, 1,2-dimethoate
Xyethane, methyl propylene carbonate, vinylene
Carbonate, r-butyrolactone, methyl propionate
At least one selected from ethyl and ethyl propionate
Can be mentioned. Also, among these, Echire
Containing carbonate and diethyl carbonate
Solvents are preferred because of their high dielectric constant and low viscosity.
Mixing of ethylene carbonate and diethyl carbonate
The ratio should be 30:70 to 40:60 by volume.
Is preferably 30:70 to 35:65.
More preferred. Here, the content of ethylene carbonate is
If it is less than 30% by volume, the electric conductivity of the non-aqueous electrolyte solution
Lower the initial capacity, output characteristics, and high temperature.
Cycle characteristics deteriorate. Also, ethylene carbonate
If the content of glass is more than 40% by volume,
The water electrolyte becomes viscous, reducing its capacity at low temperatures.
You. In the present invention, lithium ions are occluded and released.
As a negative electrode, a graphite (black)
Lead), non-graphitizable carbon (hard carbon), easily graphitizable carbon
(Soft carbon) and carbon black
Can be used in combination. [0019] The present invention will be described below with reference to examples and comparative examples.
You. Example 1 (Production of Battery) Width 42 mm, length 483 mm, thickness 20
μm aluminum foil with a spinel structure on both sides
Lithium ganate (Li_{1 + x}Mn_2-xO_Four ) Powder: 78.
2 parts by weight, lithium nickel cobaltate (LiNi_1-x
Co_xO_Two 1) 13.8 parts by weight, carbon black 5 parts by weight
Parts, a mixture consisting of 3 parts by weight of polyvinylidene fluoride,
Thickness after drying including aluminum foil is 188 μm
It was applied in the same manner to form a positive electrode. The negative electrode has a width of 43.5 mm,
A graphite powder 91 on a copper foil having a length of 513 mm and a thickness of 10 μm.
Parts by weight, carbon black 1 part by weight, polyvinyl fluoride
Thickness of a mixture consisting of 8 parts by weight of den after drying including copper foil
Was made to be 121 μm. Microporous
Polyethylene membrane separator / positive electrode / microporous polyethylene
Laminated in the order of a separator / negative electrode of a ren film and spirally wound
Then, a battery element was prepared and housed in a battery can. Inside the battery can
, 30 parts by volume of ethylene carbonate, diethyl carbonate
Concentration in a mixed solvent consisting of 70 parts by volume
M, 0.9M and 1.0M₆ To
Prepare a dissolved electrolyte solution, inject the electrolyte solution, and then close it.
Lithium ion secondary batteries with different lithium salt concentrations
And the obtained lithium ion secondary battery is connected to a terminal voltage.
Is charged with a constant current up to 4.2V, and is charged with a constant voltage from 4.2V.
6. The total charging time from the start of constant current charging after switching to electricity
Charging was completed in 5 hours. Leave them at 30 ° C for 14 days
To stabilize the battery and remove defective products.
Then, 12 were subjected to the following test. (Cycle test) 2 for each lithium salt concentration
Up to 3.0V at 45 ° C with 1C discharge rate
After discharging, constant current charging again at 1C, reaching 4.2V
Switch to constant voltage charging and start constant current charging
Charge so that the total charge time of the battery becomes 2.5 hours
Perform a cycle test to determine the initial battery capacity
The average value of the battery capacity of each battery for each cycle is
This is shown in FIG. (High temperature storage test)
The battery was discharged at a discharge rate of 1 C to obtain an initial 1 C capacity. Next
After charging, discharge at a discharge rate of 0.2 C
The capacity was 0.2 C. In addition, their capacity ratio is 1.0C capacity
/0.2C capacity was used as the initial rate characteristic. These contents
After measuring the volume, adjust the depth of discharge to different
Measure the impedance with a 1 kHz AC
The initial impedance was used. Discharge these batteries at each discharge depth.
Make two per degree, store at 60 ° C for 2 weeks,
The following test was performed. (Impedance change after storage) 2 weeks at 60 ° C
Remove the batteries after storage for a while, and
Measure dance and save against impedance before saving
The subsequent impedance is defined as the amount of impedance change, and
The average was determined for each electric charge depth and is shown in FIG. (Rate characteristics after storage) Impedance after storage
After measuring the capacitance, discharge at a discharge rate of 1 C and measure the remaining capacity.
After charging, recharge the battery and discharge at a discharge rate of 1C.
It was 1C capacity after existence. Then, after charging, release 0.2C.
The battery was discharged at the electric power to obtain a capacity of 0.2 C after storage. these
Capacitance ratio (1.0C capacity / 0.2C capacity) at 100%
Expressed as rate characteristics after storage, averaged for each discharge depth
Was obtained and shown in FIG. (Capacity maintenance rate after storage) Initial 0.2 C capacity
Ratio of 0.2C capacity after storage to 0.2C capacity after storage
Volume / initial 0.2 C capacity) expressed as a percentage and the volume after storage
The average was calculated for each discharge depth as the volume maintenance rate.
did. Comparative Example 1 The concentration of the lithium salt in the electrolyte was 0.7 M, 1.2 M,
And 1.5 M in the same manner as in Example 1.
A battery was prepared, and the battery characteristics were evaluated in the same manner as in Example 1.
The results are shown in FIGS. [0026] The non-aqueous electrolyte secondary battery of the present invention is
In the battery using the manganese composite oxide as the positive electrode,
As an active material, in addition to lithium manganese composite oxide,
Mixed with nickel-cobalt composite oxide and lithium salt
Battery concentration by setting the concentration of
A battery having good cycle characteristics can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a capacity retention ratio with respect to the number of cycles at 45 ° C. of nonaqueous electrolyte secondary batteries of Examples and Comparative Examples of the present invention. FIG. 2 is a diagram illustrating a change in impedance after storage at 60 ° C. for two weeks with respect to a lithium salt concentration in nonaqueous electrolyte secondary batteries of Examples and Comparative Examples of the present invention. FIG. 3 is a diagram for explaining rate characteristics after storage at 60 ° C. for 2 weeks with respect to lithium salt concentration of nonaqueous electrolyte secondary batteries of Examples and Comparative Examples of the present invention. FIG. 4 is a diagram for explaining a capacity retention ratio before and after storage at 60 ° C. for two weeks with respect to a lithium salt concentration of nonaqueous electrolyte secondary batteries of Examples and Comparative Examples of the present invention.

   ────────────────────────────────────────────────── ─── Continuation of front page    F term (reference) 5H029 AJ04 AJ05 AK03 AK19 AL06                       AM03 AM04 AM05 AM07 BJ14                       CJ08 HJ02 HJ10                 5H050 AA07 AA10 BA17 CA08 CA09                       CA30 CB07 GA10 HA02 HA10

Claims (1)

Claims: 1. In a non-aqueous electrolyte secondary battery using a positive electrode containing a lithium manganese composite oxide and a substance capable of inserting and extracting lithium ions as a negative electrode, a lithium manganese composite oxide is used as a positive electrode active material. Containing lithium nickel cobalt composite oxide together with a lithium salt in a non-aqueous solvent.
A non-aqueous electrolyte secondary battery, comprising: an electrolyte solution having a concentration of 8 to 1 M.