Quantifying energy dissipations and their impact on the energy efficiency of lithium-ion batteries

Abstract

Energy dissipation in lithium-ion batteries is a key indicator for evaluating and optimizing energy efficiency under various operating conditions. We proposed a theoretical hypothesis linking energy dissipation to energy efficiency and validated it using different cell chemistries and formats. Thermal characterization was performed using a custom-designed multifunctional isothermal calorimeter, and a thermal model including irreversible and reversible heat source terms was incorporated into a reduced-order electrochemical model (ROM). The model was validated using experimentally measured heat generation rate (HGR) data from charge–discharge cycles under different operating conditions. Results reveal that contact resistance dominates energy dissipation, accounting for 52–56 % of total energy dissipated. Silicon-containing anodes have higher activation losses than pure Graphite anodes due to stress-induced overpotential from Silicon volume expansion during cycling. High C-rates increase energy dissipation due to kinetic limitations, while high temperatures improve ionic conductivity and reduce charge transfer kinetics. Aging studies revealed significant increase in energy dissipation from beginning-of-life (BoL) to end-of-life (EoL), attributed to solid-electrolyte interphase (SEI) layer growth and degradation mechanisms. Cylindrical cells have higher volumetric HGR than pouch cells due to smaller surface-area-to-volume ratios. Finally, energy efficiency maps were developed as functions of state-of-charge (SOC) and C-rate, offering insights for optimizing cell operations and thermal management strategies.