Method of charging an electrochemical cell

1. A method of pulse charging a secondary electrochemical storage cell, comprising the steps of:

polarizing the cell by applying a polarizing voltage greater than about 0.1 V above the cell's rest potential for a first predetermined period of time;

depolarizing the cell for a second predetermined period of time; and

repeating the polarizing and depolarizing steps until a charging end-point is reached, wherein the cell comprises:

a negative electrode comprising an alkaline metal;

a positive electrode comprising at least one transition metal halide;

a molten salt electrolyte comprising alkaline metal haloaluminate; and

a solid electrolyte partitioning the positive electrode from the negative electrode, wherein a first surface of the solid electrolyte is in contact with the positive electrode, and a second surface of the solid electrolyte is in contact with the negative electrode.

2. The method of claim 1 , wherein the alkaline metal haloaluminate comprises sodium chloroaluminate, and the transition metal halide comprises a transition metal chloride.

3. The method of claim 1 , wherein the polarizing voltage is at least about 3% greater than a rest potential of the cell.

4. The method of claim 1 , wherein a pulse pair of one polarizing and one depolarizing step constitutes charging less than about 1/50 th of the maximum capacity of the cell.

5. The method of claim 1 , wherein the depolarizing step comprises applying a depolarization current greater than about 0.01 A to the cell for the second predetermined period of time.

6. The method of claim 5 , wherein a magnitude of the maximum depolarization current is less than about 5% of the maximum current passed through the cell during the polarization step.

7. The method of claim 5 , wherein the depolarizing current is applied for a time duration less than about 10 seconds.

8. The method of claim 5 , wherein a ratio of the first predetermined period of time to the second predetermined period is greater than about 100.

9. The method of claim 1 , wherein the depolarizing step comprises suspending current flow through the cell for the second predetermined period of time.

10. The method of claim 9 , wherein the second predetermined period of time is less than about 2 minutes.

11. The method of claim 9 , wherein a ratio of the first predetermined period of time to the second predetermined period of time is greater than about 20.

12. The method of claim 1 , wherein the positive electrode comprises nickel chloride, and wherein the polarizing voltage is in a range from about 2.65 V to about 3.2 V.

13. The method of claim 12 , wherein the polarizing voltage is in a range from about 2.7 V to about 3V.

14. A method of pulse charging a sodium metal halide cell, comprising the steps of:

polarizing the cell by applying a polarizing voltage in a range from about 2.7 V to 3.1 V to the cell for less than about 10 minutes;

depolarizing the cell, immediately after polarizing, by applying a depolarization current in a range from about 0.01 A to 0.1 A to the cell for less than about 5 seconds; and

repeating the polarizing and depolarizing of the cell sequentially at least 5 times, until a charging end-point is reached, wherein the cell comprises:

a negative electrode comprising sodium;

a positive electrode comprising nickel chloride:

a molten salt electrolyte comprising sodium chloroaluminate; and

a solid electrolyte partitioning the positive electrode from the negative electrode, wherein a first surface is in contact with the positive electrode and a second surface is in contact with the negative electrode.

15. A method of pulse charging a sodium metal halide cell, comprising the steps of:

polarizing the cell by applying a polarizing voltage in a range from about 2.7 V to 3.1 V to the cell for less than about 10 minutes;

depolarizing the cell, immediately after polarizing, by suspending current flow through the cell for less than about 1 minute; and

repeating the polarizing, and depolarizing of the cell sequentially at least 5 times, until a charging end-point is reached, wherein the cell comprises:

a negative electrode comprising sodium;

a positive electrode comprising nickel chloride;

a molten salt electrolyte comprising sodium chloroaluminate; and

a solid electrolyte partitioning the positive electrode from the negative electrode, wherein a first surface is in contact with the positive electrode and a second surface is in contact with the negative electrode.

16. A method of pulse charging a sodium metal chloride cell that comprises:

a negative electrode comprising sodium;

a positive electrode comprising nickel chloride;

a molten salt electrolyte comprising sodium chloroaluminate; and

a beta″-alumina solid electrolyte partitioning the positive electrode from the negative electrode, wherein a first surface is in contact with the positive electrode and a second surface is in contact with the negative electrode,

said method comprising the steps of:

polarizing the cell by applying a polarizing voltage greater than about 0.15 V above the cell's rest potential until the polarization in the cell is built up to a point wherein an open circuit voltage of the cell for about 10 seconds remains more than about 0.1 V above the cell's rest potential;

depolarizing the cell immediately after polarizing, by applying a depolarization current in a range from about 0.01 A to 0.1 A to the cell until the polarization in the cell is reduced to a point wherein an open circuit voltage of the cell for about 10 seconds is less than about 0.1 V above the cell's rest potential; and

repeating the polarizing, and depolarizing steps until a charging end-point is reached.