Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-01-19
2004-03-30
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231950, C429S218100, C429S231800, C429S341000, C429S330000, C429S323000, C429S249000
Reexamination Certificate
active
06713215
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention refers to a coin-type (button-shaped) non-aqueous electrolyte rechargeable battery employing a substance capable of occluding and discharging lithium as the active material for the positive electrode and negative electrode, and a lithium ion conductive non-aqueous electrolyte, particularly, to a heat resistant non-aqueous rechargeable battery suitable for reflow soldering.
2. Background Information
The use of coin-type (button-shaped) non-aqueous rechargeable battery in the field of back-up power source for electronic devices is increasing because of its advantages such as high energy density, light weight, etc.
Most of the coin-type (button-shaped) non-aqueous rechargeable batteries known heretofore required an addition of lithium to the negative electrode in some form as an active material. For instance, in case of a battery using lithium-aluminum alloy for the negative electrode and a manganese oxide containing lithium of 3-V class for the positive electrode, lithium had to be pressure-welded to the negative electrode. In case of a battery using carbon for the negative electrode and a lithium-containing manganese oxide of 3-V class for the positive electrode, lithium had to be electrochemically inserted into the negative electrode.
In the batteries above, the selection of the material for the gasket which assures the air tightness and liquid tightness of the battery, as well as the insulation of the positive electrode and negative electrode cans is particularly important. Conventionally used as the gasket material is the inexpensive polypropylene, because of its advantages in resistance against chemicals, elasticity, creep resistance, and moldability which enables injection molding.
In case of using the batteries above mainly for memory back-up power sources, the terminals for use in soldering are welded to them, and are often soldered onto the printed wiring boards together with memory devices. Conventionally, soldering irons has been used for soldering the batteries to the printed wiring boards; however, with the recent requirements for more compact electronic devices which boast high functionality, there is a demand for increasing the number of electronic components to be mounted on the same area of the printed wiring board, and this made it difficult to afford a space for inserting the soldering iron. Furthermore, to reduce the production cost, automated soldering had been keenly demanded.
In the light of the aforementioned circumstances, there is employed a method comprising applying a solder cream and the like to the portion to be soldered and then mounting the components thereon, or a method comprising, after mounting the components on the board, supplying small beads to the soldering portions, and passing the thus mounted printed wiring board through a furnace whose atmosphere thereof is maintained at a high temperature set at a range of, for instance, 200 to 230° C., thereby allowing the solder to melt and accomplish the soldering (this method is referred hereinafter as “reflow soldering”). However, the coin-type (button-shaped) non-aqueous rechargeable battery of the conventional art had not been designed to use a heat-resistant material, and this disadvantageously led to the loss of its functionality as a battery during performing reflow soldering.
Most of the 3-V class coin-type (button-shaped) non-aqueous rechargeable batteries known heretofore employ a manganese oxide or a lithium-containing manganese oxide for the positive electrode and a material to which lithium is added in some form during the production process for the negative electrode. However, the material to which lithium is added in some form loses stability during the reflow soldering.
For instance, in a 3-V class coin-type (button-shaped) non-aqueous rechargeable battery using Li
4
Mn
5
O
12
as the lithium-containing manganese oxide for the positive electrode and a lithium-aluminum alloy for the negative electrode, the lithium alloy reacts with the electrolytic solution in almost any type of combinations of electrolytic solutions and the heat-resistant battery members as to cause abrupt bulging or explosion.
Similarly, in case of a 3-V class coin-type (button-shaped) non-aqueous rechargeable battery using Li
4
Mn
5
O
12
as the lithium-containing manganese oxide for the positive electrode and carbon doped with lithium either by contact doping or by electrochemical process for the negative electrode, the electrolytic solution undergoes reaction with the lithium-doped negative electrode as to cause abrupt bulging or explosion.
Furthermore, in a coin-type (button-shaped) non-aqueous rechargeable battery of the conventional type, no material resistant to the reflow temperature is used for the electrolytic solution, separator, or gasket. Thus, this lead to problems of causing, for instance, boiling or dissolution.
SUMMARY OF THE INVENTION
In the light of the aforementioned problems, the present invention utilizes a molybdenum oxide as the active material for the positive electrode. In particular, MoO
3
was found to be favorable because it has a high potential, and hence it allows setting the battery potential at a high value. Furthermore, there has been found a heat-resistant material for the electrolytic solution, separator, gasket, or other constituent elements of the batter which does not impair the battery performance even when combined with the electrode. This makes it possible to provide a coin-type (button-shaped) non-aqueous rechargeable battery resistant to the reflow temperature.
In the case of a coin-type (button-shaped) non-aqueous rechargeable battery using a manganese oxide or lithium-containing manganese oxide or the positive electrode and a lithium-aluminum alloy or carbon doped with lithium either by contact doping or by electrochemical process for the negative electrode, in almost all of the combinations of the electrolytic solution and the heat-resistant battery members, the electrolytic solution and the lithium alloy undergo reaction during the reflow soldering is to cause an abrupt bulging or explosion, and an increase in internal resistance. In the case of using a lithium alloy negative electrode, there was a tendency of increasing the internal resistance because the negative electrode becomes unstable during the alloying or the doping of lithium.
Further, in case of sealing the positive electrode alone inside the coin battery together with the electrolytic solution, no explosion occurs even if it is heated at the reflow temperature; however, there was found a tendency to cause bulging of the coin-shaped casing. Presumably, the combination of a negative electrode containing active lithium and the manganese oxide or the lithium-containing manganese oxide accelerates the abrupt bulging or explosion, or the increase in internal resistance.
As a result of studying various types of oxides for the positive electrode, it has been found that, only in case of using a molybdenum oxide in combination with a negative electrode containing lithium in some form, particularly by using MoO
3
, a 3-V non-aqueous rechargeable battery can be stabilized specifically at the reflow temperature. The reason for this is not fully understood by principle, but the use of a molybdenum oxide for the positive electrode stabilizes the lithium-containing negative electrode at high temperatures as to considerably suppress the bulging of the battery and the increase in the internal resistance.
As the negative electrode, those which were extremely difficult for use in a battery produced by reflow process are now made usable. In case of using the negative electrode in a primary battery, metallic lithium can be used as it is. For secondary batteries, there can be used, for instance, a lithium alloy such as a lithium-aluminum, etc., or carbon doped with lithium, or a metallic oxide (e.g.e, SiO, WO
2
, WO
3
, doped with lithium.
Molybdenum oxide according to the present invention is stable at the reflow treatment temperature, and yet, it can
Harada Toyoo
Kanno Yoshimi
Onodera Hideharu
Sakai Tsugio
Takasugi Shinichi
Adams & Wilks
Sii Micro Parts Ltd.
Weiner Laura
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