Solid phase diffusivity Ds is a key parameter in Lithium-ion cell models because solid phase diffusion typically dominates the voltage transients. The Galvanostatic Intermittent Titration Technique (GITT) is easy to implement and universally accepted as the standard for diffusivity measurement, but the accuracy of GITT diffusivity measurement is unknown. This paper develops a Least Squares GITT (LS-GITT) that uses all of the voltage data from a GITT test to optimally tune the diffusivity in a reduced order solid phase diffusion model. The accuracies of the GITT and LS-GITT diffusivity measurements are evaluated using the RMS error between the model predicted and experimentally measured voltages. Basedon experimental results from a NCM half cell, LS-GITT is more accurate than GITT, of ten by an order of magnitude. The GITT test overestimates Ds because the underlying model neglects the effects of bulk capacity on the voltage transients. LS-GITT gives results accurate to 1 mV RMS from 15%-100% SOC where GITT provides the same level of accuracy over less than half that SOC range. Neither technique provides accurate Ds measurements below 10% SOC.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry