Systems and methods for determining thermal characteristics of electrochemical cells in an energy storage system

A method for determining respective thermal characteristics of a plurality of electrochemical cell assemblies in an energy storage system, the method comprising:

• at a first time, beginning recording of respective open circuit voltages of the plurality of electrochemical cell assemblies;
• after the first time but before a second time, controlling temperature control equipment of the energy storage system to change a temperature setpoint of a heat transfer fluid, the heat transfer fluid being in thermal communication with the plurality of electrochemical cell assemblies;
• at the second time, ending recording of the respective open circuit voltages of the plurality of electrochemical cell assemblies;
• generating a respective voltage profile for each electrochemical cell assembly from the respective open circuit voltages of the electrochemical cell assembly recorded from the first time to the second time;
• determining a respective electrical time constant for each electrochemical cell assembly from the respective voltage profile for the electrochemical cell assembly, the respective electrical time constant for each electrochemical cell assembly representing time for open circuit voltage of the electrochemical cell assembly to change in response to the change of the temperature setpoint of the heat transfer fluid;
• determining a respective thermal characteristic for each electrochemical cell assembly at least partially based on the respective electrical time constant for the electrochemical cell assembly;
• and
• after determining the respective thermal characteristic for each electrochemical cell assembly, controlling at least partially based on the respective thermal characteristic of one or more of the plurality of electrochemical cell assemblies one or more of (i) the temperature control equipment of the energy storage system and (ii) a battery management system (BMS) node control of the energy storage system.