Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-01-02
2001-01-09
Nuzzolillo, Maria (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231500, C429S219000
Reexamination Certificate
active
06171729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy, and more particularly, to an alkali metal electrochemical cell having an anode-to-cathode (A/C) capacity ratio specifically balanced to improve cell swelling without appreciably detracting from cathode efficiency. A preferred couple is an alkali metal/solid cathode active material and a most preferred chemistry is a lithium/transition metal oxide couple.
2. Prior Art
Lithium batteries have been successfully used to power implantable medical devices such as pacemakers, cardiac defibrillators, and the like. However, it is known that lithium batteries swell when they reach certain voltages during discharge. In the design of medical devices, this swelling must be accounted for so that enough void space is left for the battery volume change in order to prevent damage to the device circuitry. Consequently, the more swelling the battery experiences, the more void space that must be reserved, which directly impacts the device total volume. In the field of implantable medical devices, a smaller total device volume is desired. Thus, it is desirable to minimize or even eliminate the existence of swelling in lithium batteries, especially those used to power implantable medical devices, to provide a more efficient design and improve the safety characteristics of the implantable device.
A chemistry that provides high discharge capacity and high energy current pulses required for powering cardiac defibrillators and other implantable medical devices is the lithium/silver vanadium oxide (Ag
2
V
4
O
11
, SVO) couple. U.S. Pat. No. 5,458,997 to Crespi et al. describes an electrochemical cell having a lithium anode and a silver vanadium oxide cathode, wherein the cell is anode limited. This patent states that in the discharge of a conventionally balanced Li/SVO cell, the resistance increases as a function of time beginning at the second voltage plateau
310
on its discharge curve (
FIG. 5
of Crespi et al.). In that respect, Crespi et al. rebalances the cell active components to include less of the lithium and electrolyte materials than would be used in a conventionally balanced cell. The rebalanced cell has the ratio of capacity (Q
−
) of the anode divided by the capacity (Q
+
) of the cathode between 0.45 and 0.70. This rebalancing allows discharge to occur only through the first voltage plateau and the first ramp to the start of the second voltage plateau, thus avoiding that portion of the discharge curve (the second voltage plateau region) in which resistance buildup occurs in conventionally balanced Li/SVO cells. The disadvantage of this approach is a loss of cell capacity by about 250 mAh (
FIG. 6
, line
370
vs.
FIG. 7
, line
385
in Crespi et al.).
Therefore, there is a need for a lithium/transition metal oxide battery that is dischargeable to deliver the high capacity needed for powering implantable medical devices and the like, but which experiences little, if any, swelling during discharge. The cell of the present invention fulfills this need by utilizing both voltage plateaus typical in the discharge of a Li/SVO cell for high discharge capacity while at the same time the effects of cell swelling are minimized through a rebalanced anode-to-cathode (A/C) capacity ratio. Thus, by using both voltage plateaus and both ramps and by rebalancing the cell active components, the cell swelling problem is controlled without detracting from the electrochemical reactions at the electrodes. Rebalancing the active components according to the present invention is also useful for decreasing swelling in a lithium/copper silver vanadium oxide cell as well.
SUMMARY OF THE INVENTION
The object of the present invention is, therefore, to improve the cell swelling performance of an alkali metal/transition metal oxide electrochemical cell such as a lithium/silver vanadium oxide cell or a lithium/copper silver vanadium oxide cell without appreciably detracting from the cell's discharge capacity. This goal is accomplished by rebalancing the anode-to-cathode capacity ratio of the cell (based on the gram amount of active material in the anode and in the cathode) such that the cell is still capable of delivering high discharge capacity and high current pulses while at the same time minimizing case swelling typically associated with such power sources.
In the present invention, the preferred anode is lithium metal and the preferred cathode is a transition metal oxide for example, silver vanadium oxide, Ag
2
V
4
O
11
(SVO) or copper silver vanadium oxide (CSVO). The preferred electrolytes include 1.0M to 1.4M LiAsF
6
or LiPF
6
as an ion-forming alkali metal salt dissolved in solvents containing at least one high permittivity solvent such as propylene carbonate and at least one low viscosity solvent such as 1,2-dimethoxyethane. This chemistry provides a cell that delivers high discharge capacity interruptable from time to time to deliver current pulse discharges.
These and other objects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following description and to the appended drawings.
REFERENCES:
patent: 5434017 (1995-07-01), Berkowitz et al.
patent: 5458997 (1995-10-01), Crepsi et al.
Gan Hong
Takuchi Esther S.
Hodgson Russ Andrews Woods & Goodyear LLP
Nuzzolillo Maria
Wills Monique
Wilson Greatbatch Ltd
LandOfFree
Control of swelling in alkali metal electrochemical 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 Control of swelling in alkali metal electrochemical cells, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control of swelling in alkali metal electrochemical cells will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2511941