Accurate assessment of the state of charge of electrochemical cells

• US 10,556,510 B2
• Filed: 11/10/2015
• Issued: 02/11/2020
• Est. Priority Date: 04/27/2012
• Status: Active Grant

• Current Assignee: California Institute of Technology, Centre National De La Recherche Scientifique, Nanyang Technological University
• Original Assignee: California Institute of Technology
• Inventors: Yazami, Rachid
• Primary Examiner(s): Caputo, Lisa M
• Assistant Examiner(s): Soto, Janice M
• Application Number:
  US14/937,718
• Publication Number:
  US 20160146895A1
• Time in Patent Office: 1,554 Days
• CPC Class Codes: B60L 1/003 to auxiliary motors, e.g. for pumps, compressors
• CPC Class Codes: B60L 1/02 to electric heating circuits
• CPC Class Codes: B60L 2240/12 Speed
• CPC Class Codes: B60L 2240/545 Temperature
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2240/549 Current
• CPC Class Codes: B60L 2240/80 Time limits
• CPC Class Codes: B60L 2260/22 Standstill, e.g. zero speed
• CPC Class Codes: B60L 3/0046 relating to electric energy storage systems, e.g. batteries or capacitors
• CPC Class Codes: B60L 3/0053 relating to fuel cells
• CPC Class Codes: B60L 3/12 Recording operating variables ; Monitoring of operating variables
• CPC Class Codes: B60L 50/40 using propulsion power supplied by capacitors
• CPC Class Codes: B60L 58/12 responding to state of charge [SoC]
• CPC Class Codes: B60L 58/16 responding to battery ageing, e.g. to the number of charging cycles or the state of health [SoH]
• CPC Class Codes: B60L 58/25 by controlling the electric load
• CPC Class Codes: B60L 58/26 by cooling
• CPC Class Codes: B60L 58/27 by heating
• CPC Class Codes: B60L 58/32 for controlling the temperature of fuel cells, e.g. by controlling the electric load
• CPC Class Codes: B60L 58/33 by cooling
• CPC Class Codes: B60L 58/34 by heating
• CPC Class Codes: B60L 58/40 : for controlling a combination of batteries and fuel cells
• CPC Class Codes: G01R 31/367 : Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/382 : Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/3835 : involving only voltage measurements
• CPC Class Codes: G01R 31/392 : Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: H01M 10/448 : End of discharge regulating measures
• 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 10/486 : for measuring temperature
• CPC Class Codes: H01M 2010/4271 : Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
• CPC Class Codes: H01M 8/04313 : characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
• CPC Class Codes: H02J 7/0048 : Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 : Detection of state of health [SOH]
• CPC Class Codes: H02J 7/007192 : in response to temperature
• CPC Class Codes: H02J 7/04 : Regulation of charging current or voltage
• CPC Class Codes: Y02E 60/10 : Energy storage using batteries
• CPC Class Codes: Y02E 60/50 : Fuel cells
• CPC Class Codes: Y02T 10/70 : Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 90/40 : Application of hydrogen technology to transportation, e.g. using fuel cells

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.

Claims

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 (Δ

H), a change in entropy (Δ

S) and a change in free energy (Δ

G);

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 (Δ

H) and change in entropy (Δ

S).

5. The method of claim 3, wherein characterizing said state of charge of said electrochemical cell comprises comparing a change in enthalpy (Δ

H) and a change in entropy (Δ

S) 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 (Δ

H) and a change in entropy (Δ

S) 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 (Δ

H), a change in entropy (Δ

S) and a change in free energy (Δ

G), 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.