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:
cycling a lithium-ion cell to an operational discharge voltage 50 or more times;
cycling the lithium-ion cell to a sub-discharge voltage of less than 2.0 Volts;
holding the lithium-ion cell at the sub-discharge voltage for a recovery time sufficient to increase capacity of the lithium-ion cell.
2 . The process of claim 1 wherein said capacity is increased 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:
cycling a lithium-ion cell to an operational discharge voltage 50 or more times;
holding the lithium-ion cell at a sub-discharge voltage of 2.0 Volts or less for a recovery time sufficient to increase cranking amperes of an electrochemical cell at 0 degrees Celsius or lower.
7 . The process of claim 6 wherein said cranking amperes is increased 1 percent or greater.
8 . The process of claim 6 wherein said 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 cycle life of a lithium-ion cell comprising:
cycling a lithium-ion cell between a charge voltage and an operational discharge voltage for a first cycling period of 50 to 250 cycles; 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 capacity is increased 2 percent or greater.
15 . The process of claim 13 wherein said sub-discharge voltage is 1.0 Volt or less.
16 . The process of claim 13 wherein said recovery time is from 24 to 120 hours.
17 . The process of claim 13 further comprising cycling said lithium-ion cell for a second cycling period; and
repeating said step of holding.
18 . The process of claim 17 wherein said first cycling period and said second cycling period are each from 50 to 250 cycles.
19 . The process of claim 17 wherein said holding steps are at a voltage of 1.0 Volt or less.