Electrochemical Thermodynamic Measurement System

• US 20070182418A1
• Filed: 08/03/2006
• Published: 08/09/2007
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: California Institute of Technology, Centre National De La Recherche Scientifique
• Original Assignee: California Institute of Technology, Centre National De La Recherche Scientifique
• Inventors: Yazami, Rachid, Reynier, Yvan, Fultz, Brent
• Granted Patent: US 7,595,611 B2
• Time in Patent Office: Days
• US Class Current: 324/429
• CPC Class Codes: H01G 11/14 Arrangements or processes for adjusting or protecting hybrid or EDL capacitors emergency protective circuit arrangements specially adapted for capacitors, and effecting automatic switching in the event of an undesired change from normal working conditions H02H7/16; emergency protective circuit arrangements for limiting excess current or voltages without disconnection H02H9/00
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H01M 10/60 Heating or cooling; Temperature control
• CPC Class Codes: H01M 10/63 Control systems charging or discharging in response to temperature H01M10/44 , H01M10/443; measurement of temperature H01M10/48 , H01M10/486
• CPC Class Codes: H01M 6/50 Methods or arrangements for servicing or maintenance, e.g. for maintaining operating temperature constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H01M 6/5044 Cells or batteries structurally combined with cell condition indicating means
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors

Abstract

The present invention provides systems and methods for accurately characterizing thermodynamic and materials properties of electrodes and electrochemical energy storage and conversion systems. Systems and methods of the present invention are capable of simultaneously collecting a suite of measurements characterizing a plurality of interconnected electrochemical and thermodynamic parameters relating to the electrode reaction state of advancement, voltage and temperature. Enhanced sensitivity provided by the present methods and systems combined with measurement conditions that reflect thermodynamically stabilized electrode conditions allow very accurate measurement of thermodynamic parameters, including state functions such as the Gibbs free energy, enthalpy and entropy of electrode/electrochemical cell reactions, that enable prediction of important performance attributes of electrode materials and electrochemical systems, such as the energy, power density, current rate and the cycle life of an electrochemical cell.

Claims

1. A measurement system for thermodynamically evaluating an electrochemical cell having electrodes;

said system comprising;

a means for measuring open circuit voltages of said electrochemical cell as a function of time;

a composition controller electrically connected to said electrochemical cell for establishing selected electrochemical cell compositions, said composition controller capable of establishing a plurality of said selected compositions;

a temperature controller in thermal contact with said electrochemical cell for establishing a plurality of selected electrochemical cell temperatures for each of said selected compositions, thereby establishing a plurality of selected electrochemical cell temperature and composition combinations; and

an open circuit voltage analyzer for receiving open circuit voltage measurements as a function of time from said a means for measuring open circuit voltages and for identifying open circuit voltages for thermochemically stabilized conditions of said electrochemical cell for said selected electrochemical cell temperature and composition combinations.

2. The system of claim 1 wherein said means for measuring open circuit voltages is capable of measuring said open circuit voltages of said electrochemical cell with an accuracy to within 1 mV.

3. The system of claim 1 wherein said means for measuring open circuit voltages comprises a voltmeter, a multimeter, a potentiometer, or a galvanometer.

4. The system of claim 1 wherein said composition controller is an electrochemical cell charger capable of charging said electrochemical cell, an electrochemical cell discharger capable of discharging said electrochemical cell or both.

5. The system of claim 4 wherein said composition controller is capable of charging or discharging said electrochemical cell under galvanostatic conditions.

6. The system of claim 1 wherein said composition controller comprises a coulometer.

7. The system of claim 1 wherein said composition controller is capable of establishing a selected state of charge of said electrochemical cell corresponding to each of said selected electrochemical cell compositions.

8. The system of claim 1 wherein said composition controller is capable of establishing a selected state of charge of said electrochemical cell corresponding to each of said selected electrochemical cell compositions with an accuracy to within about 5%.

9. The system of claim 1 wherein said composition controller is capable of establishing open circuit voltages corresponding to each of said selected electrochemical cell compositions.

10. The system of claim 1 wherein said composition controller establishes a selected composition of at least one or said electrodes.

11. The system of claim 1 wherein said temperature controller establishes said selected electrochemical cell temperatures with an accuracy equal to or greater than about 0.1 degrees Kelvin.

12. The system of claim 1 wherein said temperature controller comprises a heater or a cooler.

13. The system of claim 1 wherein said heater or cooler is selected from the group consisting of a thermoelectric cooler, thermoelectric heater, resistive heater, temperature bath, heat pump or radiative cooler.

14. The system of claim 1 wherein said temperature controller comprises a Peltier plate thermoelectric cooler.

15. The system of claim 1 wherein said temperature controller further comprises a thermocouple in thermal contact with said electrochemical cell for measuring the temperature of said electrochemical cell.

16. The system of claim 15 wherein said temperature controller further comprises a processor for receiving temperature measurements from said thermocouple and for providing feedback control of said heater or cooler so as to establish said selected electrochemical cell temperatures.

17. The system of claim 1 wherein said open circuit voltage analyzer is a processor capable of executing an algorithm calculates observed rates of change in open circuit voltage per unit time for a selected electrochemical cell temperature and composition combination using said open circuit voltage measurements as a function of time received from said means of measuring open circuit voltage.

18. The system of claim 17 wherein said algorithm compares absolute values of said observed rates of change in open circuit voltage per unit time for said selected electrochemical cell temperature and composition combination to a threshold rate of change in open circuit voltage per unit time, and wherein said algorithm identifies an open circuit voltage equal to said open circuit voltage of said electrochemical cell for thermochemically stabilized conditions for said selected electrochemical cell temperature and composition combination when the absolute value of the observed rate of change in open circuit voltage per unit time is equal to or less than said threshold rate of change in open circuit voltage per unit time.

19. The system of claim 18 wherein said threshold rate of change in open circuit voltage as a function of time is equal to or less than 1.0 mV h⁻

1.

20. The system of claim 18 wherein said threshold rate of change in open circuit voltage as a function of time is equal to or less than 0.1 mV h⁻

1.

21. The system of claim 1 wherein said electrochemical cell is a primary battery, secondary battery, a fuel cell, a photovoltaic cell, a lithium ion battery, an electrochemical double layer capacitor or an electrochemical double layer supercapacitor.

22. The system of claim 1 wherein the selected electrochemical cell compositions correspond to compositions of one of said electrodes of said electrochemical cell.

23. The system of claim 1 wherein the selected electrochemical cell compositions correspond to states of charge of one of said electrodes of said electrochemical cell.

24. The system of claim 1 wherein one of said electrodes in an intercalating electrode, wherein the selected electrochemical cell compositions correspond to amounts of an intercalant physically associated with said intercalating electrode of said electrochemical cell.

25. The system of claim 1 wherein one of said electrodes in an intercalating electrode, wherein the selected electrochemical cell compositions correspond to different stoichiometries of an intercalant incorporated with said intercalating electrode of said electrochemical cell.

26. The system of claim 1 wherein said electrochemical cell further comprises an electrolyte in contact with one or both of said electrodes, wherein the selected electrochemical cell compositions correspond to compositions of said electrolyte of said electrochemical cell.

27. The system of claim 1 further comprising a reference electrode in electrical contact with at least one of said electrodes.

28. The system of claim 1 wherein said electrochemical cell comprises a two electrode cell comprising a counter electrode and a working electrode, wherein said counter electrode is capable of being integrated to a reference electrode.

29. The system of claim 1 wherein said electrochemical cell comprises a two electrode cell comprising a first working electrode and a second working electrode, wherein said first working electrode is a positive pole of said electrochemical cell and said second working electrode is a negative pole of said electrochemical cell, said electrochemical cell comprising a primary or secondary battery.

30. A method for thermodynamically evaluating an electrochemical cell having electrodes;

said method comprising the steps of;

controlling the composition of said electrochemical cell to establish a plurality of selected electrochemical cell compositions;

controlling the temperature of said electrochemical cell to establish a plurality of selected electrochemical cell temperatures for each of said selected

electrochemical cell compositions, thereby establishing a plurality of selected electrochemical cell temperature and composition combinations;

measuring open circuit voltages of said electrochemical cell as a function of time for said selected electrochemical cell compositions and said selected electrochemical cell temperatures; and

identifying open circuit voltages for thermochemically stabilized conditions of said electrochemical cell for said selected electrochemical cell temperature and composition combinations.

31. The method of claim 30 wherein said selected electrochemical cell compositions are established by charging or discharging said electrochemical cell.

32. The method of claim 30 wherein said step of controlling the composition of said electrochemical cell is carried out by establishing selected states of charge of said electrochemical cell corresponding to each of said selected electrochemical cell compositions.

33. The method of claim 30 wherein said step of controlling the composition of said electrochemical cell is carried out by establishing selected states of charge of one of said electrodes.

34. The method of claim 30 wherein said step of controlling the composition of said electrochemical cell is carried out by establishing open circuit voltages or state of charges corresponding to each of said selected electrochemical cell compositions.

35. The method of claim 30 wherein at least one or said electrodes is an intercalating electrode, wherein the step of controlling the composition of said electrochemical cell establishes a selected stoichiometry of an intercalator in said intercalating electrode.

36. The method of claim 30 wherein said step of identifying open circuit voltages for thermochemically stabilized conditions of said electrochemical cell comprises the steps of:

calculating observed rates of change in open circuit voltage per unit time for said combinations of selected electrochemical cell compositions and a selected electrochemical cell temperatures using said open circuit voltage measurements as a function of time.

comparing absolute values of said observed rates of change in open circuit voltage per unit time for a combination of a selected electrochemical cell composition and a selected electrochemical cell temperature to a threshold rate of change in open circuit voltage per unit time; and

identifying an open circuit voltage is equal to said open circuit voltage of said electrochemical cell for thermochemically stabilized conditions for a selected electrochemical cell composition and a selected electrochemical cell temperature when the absolute value of the observed rate of change in open circuit voltage per unit time is equal to or less than said threshold rate of change in open circuit voltage per unit time, wherein said threshold rate of change in open circuit voltage as a function of time is equal to or less than 1 mV h<sup>−

1</sup>.

37. The method of claim 30 further comprising the steps of generating plots of said open circuit voltages of said electrochemical cell for thermochemically stabilized conditions versus temperature for each of said selected electrochemical cell compositions.

38. The method of claim 37 further comprising the steps of determining slopes and intercepts for each of said plots, wherein said slopes correspond to changes in entropy for reactions at said electrodes of said electrochemical cell, and said intercepts corresponds to changes in enthalpy for reactions at said electrodes of said electrochemical cell.

39. The method of claim 37 further comprising the step of generating a plot of said changes in entropy or enthalpy versus said selected compositions.

40. The method of claim 30 comprising a method selected from the group consisting of:

a method of predicting the capacity, specific energy, power, cycle life, cell voltage, stability or discharge current of said electrochemical cell;

a method of assessing the composition, morphology, phase or physical state of said electrodes;

a method of identifying surface defects, bulk defects or crystal structure defects in said electrodes; and

a method of identifying a phase transition in said electrodes.

41. A method of characterizing an electrochemical cell or a component of said electrochemical cell, wherein said electrochemical cell has electrodes, said method comprising the steps of:

determining changes in entropy, enthalpy or free energy for reactions at one or more of said electrodes for a plurality of selected electrochemical cell compositions;

correlating said changes in entropy, enthalpy or free energy as a function of said selected electrochemical cell compositions with a characteristic of said electrochemical cell or component of said electrochemical cell.

42. The method of claim 41 further comprising the step of plotting said changes in entropy, enthalpy or free energy as a function of said selected electrochemical cell compositions.

43. The method of claim 41 wherein said selected electrochemical cell compositions correspond to compositions of an electrode of said electrochemical cell, compositions of an electrolyte of said electrochemical cell, or compositions or more than one electrode of said electrochemical cell.

44. The method of claim 41 wherein said characteristic of said electrochemical cell or component of said electrochemical cell is selected from the group consisting of:

the state of health of the electrochemical cell, the state of health of an electrode of said electrochemical cell, the state of health of an electrolyte of said electrochemical cell;

the physical state of an electrode of said electrochemical cell;

the presence of defects in an electrode of said electrochemical cell;

the phase of an electrode of said electrochemical cell;

the composition of an electrode of said electrochemical cell, and the composition or phase of an electrolyte of said electrochemical cell.

45. A method of characterizing an electrochemical cell or a component of said electrochemical cell, wherein said electrochemical cell has electrodes, said method comprising the steps of:

determining changes in entropy, enthalpy or free energy for reactions at one or more of said electrodes for a plurality of open circuit voltages of said electrochemical cell;

correlating said changes in entropy, enthalpy or free energy as a function of said open circuit voltages of said electrochemical cell with a characteristic of said electrochemical cell or component of said electrochemical cell.

46. The method of claim 45 further comprising the step of plotting said changes in entropy, enthalpy or free energy as a function of said open circuit voltages of said electrochemical cell.

47. The method of claim 45 wherein said characteristic of said electrochemical cell or component of said electrochemical cell is selected from the group consisting of:

the state of health of the electrochemical cell, the state of health of an electrode of said electrochemical cell, the state of health of an electrolyte of said electrochemical cell;

the physical state of an electrode of said electrochemical cell;

the presence of defects in an electrode of said electrochemical cell;

the phase of an electrode of said electrochemical cell;

the composition of an electrode of said electrochemical cell and the composition or phase of an electrolyte of said electrochemical cell.