Three-electrode test cell

1. A three-electrode test cell, comprising:

a negative electrode;

a positive electrode having a first aperture defined therein, the first aperture having a perimeter defining a closed curve such that the positive electrode surrounds the perimeter;

a reference electrode disposed within the first aperture of the positive electrode and physically separated from the positive electrode;

a first microporous polymer separator soaked in an electrolyte, the first microporous polymer separator being disposed between the negative electrode and the positive electrode; and

a second microporous polymer separator soaked in the electrolyte, at least a portion of the second microporous polymer separator being disposed between the negative electrode and the reference electrode, the second microporous polymer separator being concave such that the second microporous polymer separator is disposed around a portion of the reference electrode and an edge of the second microporous polymer separator is disposed between the reference electrode and the positive electrode.

2. The three-electrode test cell as defined in claim 1 , further comprising:

a negative electrode shell, wherein the negative electrode is disposed between the negative electrode shell and the first microporous polymer separator;

a positive electrode shell, wherein the positive electrode is disposed between the positive electrode shell and the first microporous polymer separator;

a spacer disposed between the negative electrode and the negative electrode shell; and

a spring disposed between the spacer and the negative electrode shell.

3. The three-electrode test cell as defined in claim 2 , further comprising a reference electrode current collector, wherein the reference electrode current collector is in electrical contact with the reference electrode.

4. The three-electrode test cell as defined in claim 3 , further comprising an insulating sealing material affixing the reference electrode current collector to the positive electrode shell.

5. The three-electrode test cell as defined in claim 4 wherein the insulating sealing material is a polyimide epoxy.

6. The three-electrode test cell as defined in claim 3 wherein the positive electrode shell has a second aperture defined therein, and wherein a portion of the reference electrode current collector is positioned within second aperture.

7. The three-electrode test cell as defined in claim 6 wherein the reference electrode current collector has a grooved portion, and wherein the grooved portion of the reference electrode current collector is positioned within the second aperture.

8. The three-electrode test cell as defined in claim 3 wherein the reference electrode current collector includes stainless steel, copper, or nickel.

9. The three-electrode test cell as defined in claim 2 , further comprising a plastic ring disposed between the positive electrode shell and the negative electrode shell such that the positive electrode shell is electrically isolated from the negative electrode shell.

10. The three-electrode test cell as defined in claim 1 wherein the reference electrode is a lithium-based reference electrode.

11. The three-electrode test cell as defined in claim 1 wherein the first microporous polymer separator has a thickness ranging from about 16 μm to about 25 μm.

12. The three-electrode test cell as defined in claim 1 wherein a sum of a positive electrode electrochemical impedance spectroscopy (EIS) and a negative electrode electrochemical impedance spectroscopy (EIS) is equal to a full cell electrochemical impedance spectroscopy (EIS).

13. The three-electrode test cell as defined in claim 1 wherein a thickness of the reference electrode is less than or equal to a thickness of the positive electrode.

14. The three-electrode test cell as defined in claim 1 wherein the first aperture is disposed near a center of the positive electrode.

15. The three-electrode test cell as defined in claim 1 wherein the reference electrode has a first dimension and the first aperture has a second dimension, the second dimension being greater than or equal to about 1.5 times to less than or equal to about 2.5 times the first dimension.

16. The three-electrode test cell as defined in claim 1 wherein the positive electrode is substantially circular.

17. The three-electrode test cell as defined in claim 1 wherein the reference electrode is substantially circular and the first aperture is substantially circular.

18. A method for simultaneously testing voltage potentials of a negative electrode and voltage potentials of a positive electrode over time, the method comprising:

electrically connecting a three-electrode test cell with at least one voltmeter, wherein the three-electrode test cell includes:

a negative electrode;

a positive electrode having an aperture defined therein, the aperture having a perimeter defining a closed curve such that the positive electrode surrounds the perimeter;

a reference electrode disposed within the aperture of the positive electrode and physically separated from the positive electrode;

a first microporous polymer separator soaked in an electrolyte, the first microporous polymer separator being disposed between the negative electrode and the positive electrode, and

a second microporous polymer separator soaked in the electrolyte, at least a portion of the second microporous polymer separator being disposed between the negative electrode and the reference electrode, the second microporous polymer separator being concave such that the second microporous polymer separator is disposed around a portion of the reference electrode and an edge of the second microporous polymer separator is disposed between the reference electrode and the positive electrode.

19. The method as defined in claim 18 wherein a sum of a positive electrode electrochemical impedance spectroscopy (EIS) and a negative electrode electrochemical impedance spectroscopy (EIS) is equal to a full cell electrochemical impedance spectroscopy (EIS).