Open-Circuit Voltage Models Should Be Thermodynamically Consistent.

Area of Science:

• Battery Technology
• Thermodynamics
• Computational Materials Science

Background:

• Open-circuit voltage (OCV) models are crucial for battery performance simulations.
• Current empirical OCV models often disregard thermodynamic principles for fitting flexibility.
• The second law of thermodynamics mandates monotonic OCV behavior with state-of-charge (SOC).

Purpose of the Study:

• To develop a thermodynamically consistent OCV model that adheres to the second law of thermodynamics.
• To enable efficient parameter optimization for OCV models using gradient-based methods.
• To integrate the new OCV model into open-source battery modeling software.

Main Methods:

• Proposed a thermodynamically consistent OCV model using differentiable thermodynamic modeling.
• Formulated the common-tangent condition as a fixed-point problem.
• Applied the implicit function theorem for gradient-based parameter optimization.
• Integrated the model with PyBaMM for pseudo-2D discharge simulations.

Main Results:

• Demonstrated the model's applicability to 12 popular electrode materials.
• Showcased seamless integration with the PyBaMM battery modeling software.
• Validated the model's thermodynamic consistency and efficiency in parameter optimization.

Conclusions:

• Thermodynamically consistent OCV models are essential for accurate Li-ion battery modeling.
• The proposed model offers a simple and efficient approach to OCV modeling.
• This work advocates for the mandatory use of thermodynamically consistent OCV models in future battery research.