Spinel-type LiMn secondary cell

Details Spinel-type LiMn secondary cell Spinel-type LiMn secondary cell

2001-09-28

2003-05-06

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Plural concentric or single coiled electrode

C429S179000, C029S623100

Reexamination Certificate

active

06558834

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a secondary cell, and more particularly to a spinel-type LiMn secondary cell.
2. Description of the Related Art
Electric vehicles and hybrid cars are presently developed as motor-driven mobile vehicles primarily for the purpose of environmental protection, and there is a demand for small, lightweight, high-performance secondary batteries as a power supply for those vehicles.
Such secondary batteries include a spinel-type LiMn secondary cell as disclosed in Japanese Patent Laid-open Publication No. 92250/1997 and Japanese Patent Laid-open Publication No. 133221/2000. The spinel-type LiMn secondary cell is small and lightweight, has a large capacity, and provides good charging characteristics and cyclic characteristics.
One conventional spinel-type LiMn secondary cell will be described below with reference to
FIG. 1
of the accompanying drawings. As shown in
FIG. 1
, the conventional spinel-type LiMn secondary cell, denoted by
100
, has cell casing
101
and electrode unit
102
housed in cell casing
101
.
Cell casing
101
comprises main member
103
and lid member
104
, each made of iron placed with nickel. Main member
103
is in the form of a hollow cylinder having a closed lower end and an open upper end. Lid member
104
is in the form of a disk closing the open upper end of main member
103
.
Lid member
104
has circular through hole
105
defined centrally therein, and is welded to the open upper end of main member
103
. Electrode unit
102
comprises a positive electrode sheet, a negative electrode sheet (both not shown), and hollow core
106
. The positive electrode sheet and the negative electrode sheet, which are laminated together with a separator sheet interposed there between, are wound into a cylindrical column around core
106
.
The positive electrode sheet has its surfaces uniformly coated with a powdery positive electrode active material (not shown), and the negative electrode sheet has its surfaces uniformly coated with a powdery negative electrode active material. The surfaces of the positive and negative electrode sheets refer to both face and back sides thereof.
The positive electrode sheet is made of pure aluminum, and the negative electrode sheet is made of pure copper. The positive electrode active material comprises a compound including lithium and manganese as indispensable constituents, and may, for example, be a powder of LiMn
2
O
4
. The negative electrode active material comprises a compound including carbon as an indispensable constituent. The gap between the sheets of electrode unit
102
is impregnated with a nonaqueous electrolytic solution.
A plurality of positive electrode tabs
107
made of pure aluminum project upwardly from an upper edge of the positive electrode sheet, and a plurality of negative electrode tabs
108
made of pure copper project downwardly from a lower edge of the negative electrode sheet. Therefore, positive electrode tabs
107
project upwardly from respective positions on the upper surface of electrode unit
102
, and negative electrode tabs
108
project downwardly from respective positions on the lower surface of electrode unit
102
.
Negative electrode tabs
108
projecting downwardly from the lower surface of electrode unit
102
are bent toward the center of electrode unit
102
, and superposed at the center of electrode unit
102
and welded directly to the inner surface of the bottom of main member
103
. Positive electrode tabs
107
projecting upwardly from the upper surface of electrode unit
102
are welded to the bottom of positive electrode member
110
.
Positive electrode member
110
is mounted in circular through hole
105
in lid member
104
by insulating members
111
,
112
.
Insulating members
111
,
112
are made of polypropylene, and are in the from of a pair of annular members held in intimate contact with lower and upper surfaces of a flange of lid member
104
that defines through hole
105
centrally in lid member
104
.
Positive electrode member
110
comprises knurled bolt
113
and knurled nut
114
, each made of pure aluminum. Knurled bolt
113
extends upwardly in through hole
105
in lid member
104
with insulating member
111
interposed between knurled bolt
113
and lid member
104
, and knurled nut
114
is threaded on knurled bolt
113
with insulating member
112
interposed between insulating member
112
and lid member
104
, thus hermetically closing cell casing
101
. Positive electrode tabs
107
are welded to the bottom of the head of knurled bolt
113
that is positioned within cell casing
101
.
Since the positive electrode sheet and the negative electrode sheet, between which the nonaqueous electrolytic solution is impregnated, develop positive and negative potentials, respectively, the threaded stud of knurled bolt
113
which projects upwardly from the upper surface of LiMn secondary cell
100
functions as a positive electrode, and the lower surface of main member
103
functions as a negative electrode.
LiMn secondary cell
100
is of a large size as a whole for use on a motor-driven mobile vehicle such as an electric vehicle. Lid member
104
of cell casing
101
is welded to main member
103
thereof for giving LiMn secondary cell
100
a desired level of mechanical strength. Therefore, main member
103
cannot be insulated from lid member
104
, which thus cannot be used as a positive electrode.
Instead, positive electrode member
110
mounted on lid member
104
by insulating members
111
,
112
functions as a positive electrode that is insulated from cell casing
101
.
Though positive electrode member
110
, positive electrode tabs
107
, and the positive electrode sheet are connected to each other, they are made of pure aluminum and are not subject to an unwanted chemical reaction such as electrolytic corrosion.
Since positive electrode member
110
comprises knurled bolt
113
and knurled nut
114
, which are generally available parts, positive electrode member
110
is simple in structure, can be constructed from an existing product, and can easily be installed on cell casing
101
.
As the threaded stud of knurled bolt
113
which functions as a positive electrode projects from cell casing
101
, it may be engaged by a positive electrode terminal of a motor-driven mobile vehicle, which may be tightened in place by a hexagonal nut (not shown) threaded over the threaded stud of knurled bolt
113
.
As described above, because lid member
104
is welded to main member
103
as a negative electrode to achieve a desired level of mechanical strength, positive electrode member
110
as a positive electrode is mounted in through hole
105
by insulating members
111
,
112
, and is made of pure aluminum as with the positive electrode sheet and positive electrode tabs
107
in order to prevent an unwanted chemical reaction.
However, inasmuch as positive electrode member
110
comprises knurled body
113
and knurled nut
114
, it suffers a lack of mechanical strength as it is made of pure aluminum. Particularly, while a positive electrode terminal can easily be attached to and removed from knurled bolt
113
by a hexagonal nut, it is highly likely for the threads of the knurled bolt
113
to be worn out when a positive electrode terminal is repeatedly attached to and removed from knurled bolt
113
.
Generally, a hexagonal nut for tightening a positive electrode terminal on knurled bolt
113
is made of iron, but not aluminum, for a reduced cost. Repeated tightening of an iron hexagonal nut on knurled bolt
113
accelerates wear on knurled bolt
113
.
When LiMn secondary cell
100
is installed on a motor-driven mobile vehicle, since LiMn secondary cell
100
is subject to frequent vibrations and stresses, knurled bolt
113
tends to be worn at an accelerated rate.
In order to solve the above problems, JP92250/1997 discloses an attempt to increase the diameter of the knurled bolt which serves as a positive electrode and also increase the size of the threads of the knurled bo

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