Active lithium replenishment to extend the life of a cell employing carbon and iron phosphate electrodes

We describe and implement a method of extending the life of a LiFePO4/graphite lithium ion battery by replenishing the lost active lithium during cell operation and concomitant capacity fade. The approach may prove helpful in terms of increasing lithium ion cell life. After the cell had lost 30% of its capacity, analysis showed that the cell had not experienced significant impedance increase or cathode capacity loss, and the anode had lost about 5% of its storage capacity. The analysis confirmed that the loss of active lithium greatly outpaced the loss of capacity for either electrode and is responsible for cell capacity decay. The cathode was then discharged against an external lithium electrode to increase the amount of active lithium within the cell. About half of the lost capacity was recovered, and the cell cycled for 1500 more cycles. Active lithium replenishment from a reserve electrode may be an effective method of extending the life of lithium ion batteries.

► We demonstrate that that active lithium can be inserted into a degraded lithium ion cell to extend its cycle life. More than 50% (0.4 A h) of the lost capacity of an EOL LiFePO4/graphite cell was recovered.
► The replenished cell was extended its battery life for more than 1500 cycles with no resistance increase. The aging behaviors of a replenished cell upon cycling was very similar that of the fresh cell.
► Our results further illustrate novel designs for lithium ion batteries where a third electrode is built in to act as an active lithium reserve, which will provide active lithium on demand.
► A major advantage of this approach is that the reserve electrode adds very little additional weight or volume to the battery, since lithium metal or other high capacity materials can be used that do not need to repeatedly cycle.