Nonaqueous electrolyte secondary cells

Details Nonaqueous electrolyte secondary cells Nonaqueous electrolyte secondary cells

2001-09-27

2004-10-26

Dove, Tracy (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S224000, C429S231300, C429S231100

Reexamination Certificate

active

06808848

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to nonaqueous electrolyte secondary cells which comprise a rolled-up electrode unit accommodated in a closed container and serving as an electricity generating element and which are adapted to deliver electric power generated by the electrode unit to the outside.
BACKGROUND OF THE INVENTION
In recent years, attention has been directed to nonaqueous electrolyte secondary cells, such as lithium ion secondary cells, as cells having a high energy density. The lithium ion secondary cell comprises, as shown in
FIGS. 1 and 2
, a cylindrical closed container
1
having a cylinder
11
and lids
12
,
12
welded to the respective ends of the cylinder, and a rolled-up electrode unit
4
enclosed in the container
1
. A pair of positive and negative electrode terminal assemblies
9
,
9
are attached to the lids
12
,
12
, respectively. Each electrode terminal assembly
9
and the rolled-up electrode unit
4
are interconnected by a current collector plate
32
and a lead portion
33
integral therewith, whereby the electric power generated by the electrode unit
4
can be delivered to the outside from the pair of terminal assemblies
9
,
9
. Each lid
12
is provided with a pressure-relief gas vent valve
13
.
As shown in
FIG. 3
, the rolled-up electrode unit
4
comprises a positive electrode
41
and a negative electrode
43
which are each in the form of a strip and which are lapped over and displaced from each other with a separator
42
interposed therebetween and rolled up into a spiral form. The positive electrode
41
comprises a current collector
45
in the form of aluminum foil and coated with a positive electrode active substance
44
. The negative electrode
43
comprises a current collector
47
in the form of copper foil and coated with a negative electrode active substance
46
. The active substance
44
of the positive electrode
41
is opposed to the active substance
46
of the negative electrode
43
with the separator
42
interposed therebetween. The positive electrode active substance is a lithium-transition metal composite oxide, while the negative electrode active substance is metallic lithium, alloy for absorbing or desorbing lithium ions or carbon material.
In the charge-discharge reaction of the cell, lithium ions move between the positive electrode active substance
44
and the negative electrode active substance
46
which face each other with an electrolyte positioned therebetween. Stated more specifically, lithium ions migrate from the negative electrode active substance
46
toward the positive electrode active substance
44
and are inserted into the active substance
44
during discharging. During charging, on the other hand, lithium ions are released from the positive electrode active substance
44
, migrate toward the negative electrode active substance
46
and are inserted into the active substance
46
.
Useful positive electrode active substances are lithium-transition metal composite oxides such as lithium-cobalt composite oxide (LiCoO
2
), lithium-nickel composite oxide (LiNiO
2
) and lithium-manganese composite oxide (LiMn
2
O
4
). The use of the lithium-transition metal composite oxide as the positive electrode active substance provides a lithium ion secondary cell of four-volt class in discharge voltage and having a high energy density.
Of the lithium-transition metal composite oxides given above, lithium-manganese composite oxide (LiMn
2
O
4
) is most favorable with respect to the cost of material and stability of supply. However, this oxide is not widely used industrially partly because it is not as satisfactory as the other lithium-transition metal oxides, i.e., lithium-cobalt composite oxide (LiCoO
2
) and lithium-nickel composite oxide (LiNiO
2
), in charge-discharge characteristics, reducing markedly in cell capacity in the case where the cell is charged and discharged at increasing charge-discharge current values.
In order to prevent deterioration in preservation characteristics, i.e., a reduction in the cell capacity, when the cell is allowed to stand for a prolonged period of time without charging and discharging, and to prevent deterioration in life characteristics, i.e. a diminution in cell capacity, in the case where the cell is repeatedly charged and discharged, studies are underway on lithium ion secondary cells (Japanese Patent No. 3024636) wherein the positive electrode active substance is a mixture of lithium-manganese composite oxide (LiMn
2
O
4
) and a lithium-nickel composite oxide [LiNi
(1−x)
M
x
O
2
wherein 0<x≦0.5, and M is at least one metal element selected from the group consisting of Co, Mn, Al, Fe, Cu and Sr], and on the partial substitution of an element other than Mn for the Mn in lithium-manganese composite oxide (LiMn
2
O
4
).
Nonaqueous electrolyte secondary cells for use in electric vehicles are used under severe conditions involving repetitions of charging and discharging with a great current within a short period of time, and charge-discharge characteristics under such conditions need to be investigated. However, the research on and improvements in lithium ion secondary cells heretofore made are limited almost always to the preservation characteristics and life characteristics as stated above, and exhaustive research still remains to be made on charge-discharge characteristics under conditions involving repetitions of charging and discharging with a great current within a short period of time, i.e., power characteristics. We checked conventional lithium ion secondary cells wherein the positive electrode active substance used is lithium-manganese composite oxide, lithium-nickel composite oxide or a mixture thereof for the evaluation of power characteristics, but were unable to obtain satisfactory results.
SUMMARY OF THE INVENTION
An object of the present invention is to give improved power characteristics to lithium ion secondary cells wherein the positive electrode active substance used is a mixture of lithium-nickel-cobalt-manganese composite oxide and lithium-manganese composite oxide.
Accordingly, we have carried out intensive research to fulfill the above object and consequently found that the power characteristics of lithium ion secondary cells are greatly influenced by the composition of lithium-nickel-cobalt-manganese composite oxide, the composition of lithium-manganese composite oxide, the mixing ratio of these two kinds of composite oxides and the average diameter of particles of the two kinds of composite oxides to accomplish the present invention.
The present invention provides a lithium ion secondary cell wherein a positive electrode active substance comprises a mixture of a lithium-nickel-cobalt-manganese composite oxide represented by the formula LiNi
(1−x−y)
Co
x
Mn
y
O
2
wherein 0.5<x+y<1.0 and 0.1<y<0.6 and a lithium-manganese composite oxide represented by the formula Li
(1+z)
Mn
2
O
4
wherein 0≦z≦0.2.
The positive electrode active substance of the lithium ion secondary cell embodying the present invention contains the lithium-nickel-cobalt-manganese composite oxide of the formula LiNi
(1−x−y)
Co
x
Mn
y
O
2
wherein 0.5<x+y<1.0 and 0.1<y<0.6. Presumably, this component gives the active substance a structure permitting lithium ions to be readily inserted into and released from the active substance.
Further by mixing the lithium-nickel-cobalt-manganese composite oxide represented by the formula LiNi
(1−x−y)
Co
x
Mn
y
O
2
wherein 0.5<x+y<1.0 and 0.1<y<0.6 with the lithium-manganese composite oxide represented by the formula Li
(1+z)
Mn
2
O
4
wherein 0≦z≦0.2 and having a spinel structure, the particles of these oxides are held in contact with one another with good stability, presumably resulting in the ease of migration of electric charges in the case where the cell is repeatedly charged and discharged with a great current within a short period of time. It is therefore thought that the lithium ion seco

Affiliated with

Also associated with

Rating

Nonaqueous electrolyte secondary cells does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Nonaqueous electrolyte secondary cells, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nonaqueous electrolyte secondary cells will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3317535