Accurate assessment of the state of charge of electrochemical cells

Patent metadata

Field	Value
Publication number	US-10556510-B2
Application number	US-201514937718-A
Country	US
Kind code	B2
Filing date	Nov 10, 2015
Priority date	Apr 27, 2012
Publication date	Feb 11, 2020
Grant date	Feb 11, 2020

Abstract

Provided are methods, systems and devices for thermodynamically evaluating electrochemical systems and components thereof, including electrochemical cells such as batteries. The present systems and methods are capable of monitoring selected electrochemical cell conditions, such as temperature, open circuit voltage and/or composition, and carrying out measurements of a number of cell parameters, including open circuit voltage, time and temperature, with accuracies large enough to allow for precise determination of thermodynamic state functions and materials properties relating to the composition, phase, states of charge, health and safety and electrochemical properties of electrodes and electrolytes in an electrochemical cell. Thermodynamic measurement systems of the present invention are highly versatile and provide information for predicting a wide range of performance attributes for virtually any electrochemical system having an electrode pair.

First claim

I claim:

1. A method for characterizing the state of charge of an electrochemical cell, said method comprising the steps of:
generating a multidimensional state of charge profile corresponding to said electrochemical cell;
measuring a plurality of open circuit voltages of said electrochemical cell via a voltage monitoring circuit, said plurality of open circuit voltages corresponding to a plurality of temperatures of said electrochemical cell;
determining a plurality of thermodynamic parameters corresponding to said electrochemical cell via a thermodynamic measurement circuit, wherein said thermodynamic parameters are selected from the group comprising: a change in enthalpy (ΔH), a change in entropy (ΔS) and a change in free energy (ΔG);
characterizing said state of charge of said electrochemical cell using said multidimensional state of charge profile and said thermodynamic parameters via a state of charge calculating circuit; and
determining a state of safety of said electrochemical cell using said state of charge determined for said electrochemical cell, wherein said state of safety is determined by using said state of charge and a temperature of said plurality of temperatures to calculate the probability of a thermal runaway corresponding to said electrochemical cell, wherein said state of safety is a function of the probability of a thermal runaway; and wherein said state of safety corresponds to an onset temperature of a thermal event within said electrochemical cell at said state of charge.

2. The method of claim 1 , comprising measuring said plurality of temperatures of said electrochemical cell.

3. The method of claim 1 , wherein said multidimensional state of charge profile is defined by at least three variables.

4. The method of claim 3 , wherein said multidimensional state of charge profile is a nonlinear function relating state of charge to change in enthalpy (ΔH) and change in entropy (ΔS).

5. The method of claim 3 , wherein characterizing said state of charge of said electrochemical cell comprises comparing a change in enthalpy (ΔH) and a change in entropy (ΔS) determined for said electrochemical cell to said multidimensional state of charge profile to determine said state of charge of said electrochemical cell.

6. The method of claim 3 , wherein characterizing said state of charge of said electrochemical cell comprises identifying the state of charge corresponding to a change in enthalpy (ΔH) and a change in entropy (ΔS) determined for said electrochemical cell for said multidimensional state of charge profile.

7. The method of claim 1 , wherein said step of generating a multidimensional state of charge profile comprises:
generating a plurality of different states of charge for said electrochemical cell; and
measuring said thermodynamic parameters corresponding to each of said plurality of states of charge; wherein said thermodynamic parameters are selected from the group comprising: a change in enthalpy (ΔH), a change in entropy (ΔS) and a change in free energy (ΔG), thereby generating said multidimensional state of charge profile.

8. The method of claim 7 , wherein said step of generating a plurality of states of charge is carried out stepwise by increasing or decreasing said state of charge of said electrochemical cell.

9. The method of claim 7 , wherein said plurality of states of charge are measured using a charge calculating circuit.

10. The method of claim 1 , further comprising selectively adjusting the temperature said electrochemical cell so as to establish said plurality of temperatures of said electrochemical cell.

11. The method of claim 1 , wherein said plurality of temperatures of said electrochemical cell are established by in situ temperatures changes of said electrochemical cell during use.

12. The method of claim 1 , wherein said open circuit voltages of said electrochemical cell are each independently measured to a margin of error less than or equal to 0.01 mV and wherein said temperatures of said electrochemical cell are independently measured to a margin of error less than or equal to 0.01 K.

13. The method of claim 1 , wherein said open circuit voltages of said electrochemical cell independently correspond to thermochemically stabilized conditions.

14. The method of claim 13 , wherein said step of measuring a plurality of open circuit voltages comprises independently determining a plurality of observed rates of change in open circuit voltage per unit time for each corresponding temperature.

15. The method of claim 14 , wherein an absolute value of said change in open circuit voltage per unit time is compared to a threshold open circuit voltage per unit time corresponding to said temperature, wherein said thermochemically stabilized conditions correspond to conditions of said absolute value of said change in open circuit voltage per unit time less than said threshold open circuit voltage per unit time.

16. The method of claim 15 , wherein said threshold open circuit voltage per unit time in open circuit voltage per unit time is less than or equal to 1.0 mV h −1 .

17. The method of claim 1 , further comprising determining a state of health of said electrochemical cell using said state of charge determined for said electrochemical cell, wherein said state of health is determined by comparing said determined state of charge with a threshold state of charge, wherein said threshold state of charge is a maximum state of charge from an electrochemical cell provided in a new condition.

18. The method of claim 1 , wherein said open circuit voltages of said electrochemical cell are each independently measured to a margin of error less than or equal to 0.1 mV and wherein said temperatures of said electrochemical cell are independently measured to a margin of error less than or equal to 0.1 K.

Assignees

• California Inst Of Techn
• Centre Nat Rech Scient
• Univ Nanyang Tech

Inventors

• Yazami Rachid

Classifications

• B60L58/40

  for controlling a combination of batteries and fuel cells · CPC title

• H02J7/84

  Control of state of health [SOH] · CPC title

• H02J7/975

  in response to temperature · CPC title

• H02J7/82

  Control of state of charge [SOC] · CPC title

• H01M8/04313

  characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function · CPC title