Control-oriented physics-based calendar life model for lithium ion cells
A physics-based calendar life model for determining the state of health of a lithium ion battery cell. The model accounts for parasitic reactions on anode and cathode particles to accurately determine degradation of a battery. By incorporating electrolyte decomposition in a cathode, the present calendar model can predict capacity retention as well as the substantial rise of cell resistance at high state of charge (SOC) and temperatures. The present calendar model is a simple algorithm, utilizing only three parameters, and determines the capacity retention and resistance rise based on temperature, SOC and time.
1. A non-transitory computer readable storage medium having embodied thereon a program, the program being executable by a processor to perform a method for determining a calendar model for a battery cell, comprising:
accessing an initial charge capacity and resistance at a first time by a battery management system for the battery cell;
determining a first temperature and a first state of charge for the battery cell at the first time;
determining a second temperature and a second state of charge for the battery cell at a second time;
based on a change in temperature between the first temperature and the second temperature for the battery cell or a change in state of charge between the first state of charge and the second state of charge for the battery cell, determining a capacity drop for the battery cell based on the second temperature and at least one first physics-based property of the battery cell at the second time:
determining a resistance growth for the battery cell based on the second temperature and at least one second physics-based property of the battery cell at the second time; and
determining a calendar fade time based on the capacity drop and the resistance growth.
2. The non-transitory computer readable storage medium of claim 1 , wherein the at least one first physics-based property comprises molecular weight and solid electrolyte interphase density.
3. The non-transitory computer readable storage medium of claim 1 , wherein the at least one second physics-based property comprises solid electrolyte interphase thickness.
4. The non-transitory computer readable storage medium of claim 1 , wherein the change in temperature between the first temperature and the second temperature is greater than a threshold temperature change.
5. The non-transitory computer readable storage medium of claim 1 , wherein the change in state of charge between the first state of charge and the second state of charge is greater than a threshold state of charge change.
6. The non-transitory computer readable storage medium of claim 1 , wherein determining the capacity drop comprises determining a thickness of a solid electrolyte interphase layer for the battery cell.
7. The non-transitory computer readable storage medium of claim 1 , wherein determining the resistance growth comprises determining a direct current resistance for an anode of the battery cell and a direct current resistance for a cathode of the battery cell.
8. A system for determining a calendar model for a battery cell, comprising:
one or more processors,
memory, and
a battery management system stored in the memory and executable by the one or more processors to:
access an initial charge capacity and resistance at a first time by the battery management system for the battery cell
determine a first temperature and a first state of charge for the battery cell at the first time,
determine a second temperature and a second state of charge for the battery cell at a second time,
based on a change in temperature between the first temperature and the second temperature for the battery cell or a change in state of charge between the first state of charge and the second state of charge for the battery cell, determine a capacity drop for the battery cell based on the second temperature and at least one first physics-based property of the battery cell at the second time,
determine a resistance growth for the battery cell based on the second temperature and at least one second physics-based property of the battery cell at the second time, and
determine a calendar fade time based on the capacity drop and the resistance growth.
9. The system of claim 8 , wherein the at least one first physics-based property comprises molecular weight and solid electrolyte interphase density.
10. The system of claim 8 , wherein the at least one second physics-based property comprises solid electrolyte interphase thickness.
11. The system of claim 8 , wherein the change in temperature between the first temperature and the second temperature is greater than a threshold temperature change.
12. The system of claim 8 , wherein the change in state of charge between the first state of charge and the second state of charge is greater than a threshold state of charge change.
13. The system of claim 8 , wherein the determining the capacity drop comprises determining a thickness of a solid electrolyte interphase layer for the battery cell, and determining the resistance growth comprises determining a direct current resistance for an anode of the battery cell and a direct current resistance for a cathode of the battery cell.
14. A method for determining a calendar model for a battery cell, comprising:
accessing an initial charge capacity and resistance at a first time;
determining a first temperature and a first state of charge for the battery cell at the first time;
determining a second temperature and a second state of charge for the battery cell at a second time;
based on a change in temperature between the first temperature and the second temperature for the battery cell or a change in state of charge between the first state of charge and the second state of charge for the battery cell, determining a capacity drop for the battery cell based on the second temperature and at least one first physics-based property of the battery cell at the second time;
determining a resistance growth for the battery cell based on the second temperature and at least one second physics-based property of the battery cell at the second time; and
determining a calendar fade time based on the capacity drop and the resistance growth.
15. The method of claim 14 , wherein the at least one first physics-based property comprises molecular weight and solid electrolyte interphase density.
16. The method of claim 14 , wherein the at least one second physics-based property comprises solid electrolyte interphase thickness.
17. The method of claim 14 , wherein the change in temperature between the first temperature and the second temperature is greater than a threshold temperature change.
18. The method of claim 14 , wherein the change in state of charge between the first state of charge and the second state of charge is greater than a threshold state of charge change.
19. The method of claim 14 , wherein determining the capacity drop comprises determining a thickness of a solid electrolyte interphase layer for the battery cell.
20. The method of claim 14 , wherein determining the resistance growth comprises determining a direct current resistance for an anode of the battery cell and a direct current resistance for a cathode of the battery cell.