Fuel gauge for an alkali metal electrochemical cell
First Claim
Patent Images
1. In combination with an implantable medical device requiring a substantially constant discharge rate during a medical device monitoring function and at least one pulse discharge for a medical device operating function, the combination comprising:
- a) an electrochemical cell comprising an alkali metal anode and a solid cathode activated with a nonaqueous electrolyte wherein the cell has a determinable stoichiometric capacity;
b) electronic circuitry powered by the electrochemical cell for discharging the cell under a first load condition and at a second, lighter load or at an open circuit voltage condition, wherein the first load occurs during a medical device operating mode for charging a capacitor or delivering therapy and the second load occurs during a medical device monitoring mode; and
c) wherein the electronic circuitry provides for determining the remaining discharge capacity in the cell by having the first load condition removed from the cell at a first time so that the cell'"'"'s discharge voltage relaxes from a first voltage at the first load to a second voltage at a second, lighter load or at an open circuit voltage condition and wherein the voltage change from the first voltage to the second voltage is measurable and wherein the time interval for the cell to relax from the first voltage at the first time to the second voltage at the second time is measurable and wherein the voltage change is divisible by the time interval to determine a Δ
OCV/Δ
Hrs ratio and wherein the depth-of-discharge ratio for the cell is then determinable using the equation;
DOD=e[−
5.00−
2.44 ln(Δ
OCV/Δ
Hrs)].
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Abstract
A “fuel gauge” for a pulse dischargeable alkali metal/solid cathode cell is described. The rate of voltage recovery is used to determine the state of charge of the cell. Voltage recovery includes recovery from one load to a second, lighter load, or a loaded condition to OCV. The present invention is particularly useful as an end-of-life indicator for a Li/CFx cell powering an implantable medical device.
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Citations
26 Claims
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1. In combination with an implantable medical device requiring a substantially constant discharge rate during a medical device monitoring function and at least one pulse discharge for a medical device operating function, the combination comprising:
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a) an electrochemical cell comprising an alkali metal anode and a solid cathode activated with a nonaqueous electrolyte wherein the cell has a determinable stoichiometric capacity;
b) electronic circuitry powered by the electrochemical cell for discharging the cell under a first load condition and at a second, lighter load or at an open circuit voltage condition, wherein the first load occurs during a medical device operating mode for charging a capacitor or delivering therapy and the second load occurs during a medical device monitoring mode; and
c) wherein the electronic circuitry provides for determining the remaining discharge capacity in the cell by having the first load condition removed from the cell at a first time so that the cell'"'"'s discharge voltage relaxes from a first voltage at the first load to a second voltage at a second, lighter load or at an open circuit voltage condition and wherein the voltage change from the first voltage to the second voltage is measurable and wherein the time interval for the cell to relax from the first voltage at the first time to the second voltage at the second time is measurable and wherein the voltage change is divisible by the time interval to determine a Δ
OCV/Δ
Hrs ratio and wherein the depth-of-discharge ratio for the cell is then determinable using the equation;
DOD=e[−
5.00−
2.44 ln(Δ
OCV/Δ
Hrs)].- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for determining the remaining discharge capacity in an electrochemical cell, comprising the steps of:
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a) providing the electrochemical cell comprising a lithium anode and a fluorinated carbon cathode activated with a nonaqueous electrolyte;
b) determining a stoichiometric capacity of the cell;
c) discharging the cell under a first load condition;
d) removing the first load from the cell at a first time so that the cell'"'"'s discharge voltage relaxes from a first voltage at the first load to a second voltage at a second, lighter load or at an open circuit voltage condition and measuring the voltage change from the first voltage to the second voltage;
e) measuring the time interval for the cell to relax from the first voltage at the first time to the second voltage at the second time;
f) dividing the voltage change by the time interval to determine Δ
OCV/Δ
Hrs ratio; and
g) computing the depth of discharge equaling e[−
5.00−
2.44 ln(Δ
OCV/Δ
Hrs)].- View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A method for determining the remaining discharge capacity in an electrochemical cell, comprising the steps of:
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a) providing an electronic device powered by the electrochemical cell;
b) providing the electrochemical cell comprising a lithium anode and a fluorinated carbon cathode activated with a nonaqueous electrolyte;
c) determining a stoichiometric capacity of the cell;
d) discharging the cell under a first load condition;
e) removing the first load from the cell at a first time so that the cell'"'"'s discharge voltage relaxes from a first voltage at the first load to a second voltage at a second, lighter load or at an open circuit voltage condition and measuring the voltage change from the first voltage to the second voltage;
f) measuring the time interval for the cell to relax from the first voltage at the first time to the second voltage at the second time;
g) dividing the voltage change by the time interval to determine a Δ
OCV/Δ
Hrs ratio; and
h) computing the depth of discharge equaling e[−
5.00−
2.44 ln(Δ
OCV/Δ
Hrs)].
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Specification