Multifunctional mixed metal olivines for lithium ion batteries

1. A method for monitoring and maintaining the performance of an electrochemical cell, comprising:

providing an electrochemical cell having a positive electrode and negative electrode separated by an electrolyte, the composition of electroactive materials of the positive electrode, the negative electrode, or both selected to provide a cell having a plurality of open circuit voltages at different states of charge, said composition selected to provide a change in voltage of the cell at a pre-selected state of charge;

monitoring the cell to detect a change in cell voltage; and

changing a current or power into or out of the cell in response to the detected change in voltage.

2. The method of claim 1 , wherein the positive electrode electroactive materials are selected to provide a cell having a plurality of open circuit voltages at different states of charge.

3. The method of claim 1 , wherein the negative electrode electroactive materials are selected to provide a cell having a plurality of open circuit voltages at different states of charge.

4. The method of claim 1 , wherein the positive electrode and negative electrode electroactive materials are selected to provide a cell having a plurality of open circuit voltages at different states of charge.

5. The method of claim 1 , wherein the positive electrode electroactive material comprises a primary electroactive material and a high voltage indicator, said high voltage indicator having an equilibrium potential that results in a cell voltage that is close to but below a first pre-selected voltage threshold.

6. The method of claim 5 , wherein the negative electrode electroactive material comprises a primary electroactive material and a low voltage indicator, said low voltage indicator having an equilibrium potential that results in a cell voltage that is close to but above a second pre-selected voltage threshold.

7. The method of claim 6 , wherein the low voltage indicator is subjected to lithiation prior to being added to the electrode.

8. The method of claim 1 , wherein the positive electrode electroactive material comprises a primary electroactive material and a low voltage indicator, said low voltage indicator having an equilibrium potential that results in a cell voltage that is close to but above a pre-selected voltage threshold.

9. The method of claim 8 , wherein the low voltage indicator is subjected to lithiation prior to being added to the electrode.

10. The method of claim 8 , wherein the primary electroactive material comprises a lithium metal phosphate and the low voltage indicator comprises a lithium metal oxide.

11. The method of claim 10 , wherein the low voltage indicator comprises LiAl x Mn 1−x O 2 where 0≦x<0.05.

12. The method of claim 8 , wherein the low voltage indicator comprises Li 2 FeSiO 4 .

13. The method of claim 8 , wherein the primary electroactive material comprises a lithium metal phosphate and the low voltage indicator comprises lithium Ti, Mg or Zr phosphate.

14. The method of claim 1 , wherein the positive electrode electroactive material comprises a primary electroactive material; a high voltage indicator, said high voltage indicator having an equilibrium potential that results in a cell voltage that is close to but below an upper limiting voltage of the cell; and a low voltage indicator, said low voltage indicator having an equilibrium potential that results in a cell voltage that is close to but above a lower limiting voltage of the cell.

15. The method of claim 14 , wherein the low voltage indicator is subjected to lithiation prior to being added to the electrode.

16. The method of claim 1 , wherein the negative electrode electroactive material comprises a primary electroactive material and a low voltage indicator, said low voltage indicator having an equilibrium potential that results in a cell voltage that is close to but above a lower limiting voltage of the cell.

17. The method of claim 16 , wherein the low voltage indicator is subjected to lithiation prior to being added to the electrode.

18. The method of claim 1 , wherein the positive electrode electroactive material comprises lithium metal phosphate.

19. The method of claim 1 , wherein the positive electrode electroactive material comprises

about 60-95 molar % of a first primary electroactive material, wherein the first primary electroactive material is a lithium metal phosphate;

about 0-50 molar % of a second primary electroactive material;

about 1-30 molar % of a high voltage indicator material having an open-circuit potential greater than each of the first and second primary electroactive materials; and

about 1-30 molar % of a low voltage indicator material having an open-circuit potential less than each of the first and second primary electroactive materials.

20. The method of claim 1 , wherein the positive electrode electroactive material comprises an olivine lithium metal phosphate material having the formula Li x M′ y M″ z M′″ w PO 4 , wherein

M′ is one or more of Mn and Fe;

M″ is one or more of Mn, Co and Ni;

M′″ is one or more of Ti, Zr and Mg;

M′ is not the same as M″;

0≦x≦1.2; 0.5≦y≦0.95; 0.025≦z≦0.5; 0.025≦w≦0.25; and

0.8≦y+z+w≦1.2.

21. The method of claim 1 , wherein monitoring the cell to detect a change in voltage comprises measuring the voltage or monitoring the first or second derivative of the voltage with respect to time or capacity.

22. The method of claim 21 , wherein impedance compensation is employed in measuring the voltage.

23. The method of claim 1 , wherein the current is changed by limiting the charge or discharge current into the cell.

24. The method of claim 1 , wherein the current is changed by decreasing the rate of charge or discharge.

25. The method of claim 1 , wherein the current is changed by terminating charge or discharge.

26. The method of claim 1 , wherein the current is changed by switching from a charging state to a discharging state.

27. The method of claim 1 , wherein the current is changed by switching from a discharging state to a charging state.

28. The method of claim 8 , wherein the low voltage indicator comprises Li 7 Ti 5 O 12 .