DEEP-DISCHARGE CONDITIONING FOR LITHIUM-ION CELLS
A process of reconditioning a lithium-ion cell is provided that unexpectedly improves cell capacity, reduces cold temperature impedance and increases cold cranking amps. The process involves a reconditioning step of holding a cell at a sub-discharge voltage for a recovery time. The sub-discharge voltage is 1.0V or less in many embodiments, optionally 0.0V. Holding this sub-discharge voltage for a recovery time of several hours will result in recovery of lost capacity that is in excess of that explainable by recovery of ions transferred to an anode overhang.
1 . A process for reconditioning an electrochemical cell comprising:
holding a lithium-ion cell at a sub-discharge voltage of 2.0 Volts or less for a recovery time sufficient to show an increased capacity relative to an untreated cell.
2 . The process of claim 1 wherein said capacity increase is 2 percent or greater.
3 . The process of claim 1 wherein said sub-discharge voltage is 1.0 Volts or less.
4 . The process of claim 1 wherein said sub-discharge voltage is 0 Volts.
5 . The process of claim 1 wherein said recovery time is 1 hour or greater.
6 . A process increasing cranking amperes of an electrochemical cell at a temperature less than 25 degrees Celsius comprising:
holding a lithium-ion cell at a sub-discharge voltage of 2.0 Volts or less for a recovery time sufficient to show increased cranking amperes of an electrochemical cell at 0 degrees Celsius or lower relative to an untreated cell.
7 . The process of claim 6 wherein said cold cranking amperes is increased 1 percent or greater relative to said untreated cell.
8 . The process of claim 6 wherein said reduced temperature is −20 degrees Celsius or lower.
9 . The process of claim 6 wherein said sub-discharge voltage is 1.0 Volts or less.
10 . The process of claim 6 wherein said sub-discharge voltage is 0 Volts.
11 . The process of claim 6 wherein said recovery time is 1 hour or greater.
12 . The process of claim 6 wherein said sub-discharge voltage is less than 2.0 Volts and said recovery time is 24 hours or greater.
13 . A process of increasing the cycle life of a lithium-ion cell comprising:
cycling a lithium-ion cell between a charge voltage and a discharge voltage for a first cycling period; and
holding said lithium-ion cell at a sub-discharge voltage of 2.0 Volts or less for a recovery time sufficient to show an increased capacity for 10 or more cycles.
14 . The process of claim 13 wherein said increased capacity is 2 percent or greater.
15 . The process of claim 13 wherein said first cycling period is from 50 to 250 cycles.
16 . The process of claim 13 wherein said sub-discharge voltage is 1.0 Volt or less.
17 . The process of claim 13 wherein said recovery time is from 24 to 120 hours.
18 . The process of claim 13 further comprising cycling said cell for a second cycling period; and
repeating said step of holding.
19 . The process of claim 18 wherein said first cycling period and said second cycling period are each from 50 to 250 cycles.
20 . The process of claim 18 wherein said both holding steps are at a voltage of 1.0 Volt or less.