Lithium reservoir system and method for rechargeable lithium ion batteries

1. A method to replenish lithium-ion capacity of a battery cell including two working electrodes and an auxiliary electrode, the method comprising:

measuring an open circuit potential of each of the two working electrodes using the auxiliary electrode as a reference electrode during an equilibrium state of the working electrodes at open circuit;

determining a state of charge of each of the two working electrodes based on the measured open circuit potential of each of the two working electrodes; and

transferring lithium from the auxiliary electrode to at least one of the two working electrodes based on the determined state of charge,

wherein:

the battery cell includes:

a first separator region arranged between the two working electrodes to separate the two working electrodes so that none of the two working electrodes are electronically connected within the cell; and

a second separator region arranged between the auxiliary electrode and the two working electrodes to separate the auxiliary electrode from the two working electrodes so that none of the two working electrodes is electronically connected to the auxiliary electrode within the cell;

the two working electrodes include a negative electrode and a positive electrode;

each of the two working electrodes includes an active material, an inert material, an electrolyte, and a current collector; and

the auxiliary electrode includes a lithium reservoir.

2. The method of claim 1 , wherein the transfer of lithium accommodates loss of capacity due to a side reaction.

3. The method of claim 1 , wherein lithium is transferred between the two working electrodes through the first separator region.

4. The method of claim 1 , wherein the first separator region includes an electrolyte with a lithium cation.

5. The method of claim 1 , wherein the second separator region includes an electrolyte with a lithium cation.

6. The method of claim 1 , wherein:

a power supply is connected to the current collector of each of the two working electrodes to charge the two working electrodes;

a first electronic circuit connects the power supply to the current collector of each of the two working electrodes; and

a second electronic circuit connects the current collector of at least one of the two working electrodes to the auxiliary electrode.

7. The method of claim 6 , wherein the second electronic circuit includes:

a variable load resistor and a switch connected in series between the current collector and the auxiliary electrode.

8. The method of claim 7 , wherein:

a battery management system controls the variable load resistor and the switch.

9. The method of claim 8 , wherein the battery management system determines the state of charge.

10. The method of claim 8 , wherein the battery management system determines at what point to open the second electronic circuit, and a rate of transfer of lithium from the lithium reservoir.

11. The method of claim 1 , wherein an electronic circuit connects at least one of the two working electrodes to the auxiliary electrode so that when the circuit is closed electrons flow from the auxiliary electrode to the at least one working electrode, and lithium ions flow concurrently through the second separator from the auxiliary electrode to the at least one working electrode.

12. The method of claim 11 , further comprising:

monitoring and controlling the transfer of lithium via a battery monitoring system.

13. The method of claim 12 , wherein the battery management system determines at what point to open the electronic circuit, and a rate of transfer of lithium from the lithium reservoir.