Physics-Based Modelling of Hybrid Cathode Li/CFx-SVO Batteries Under Pulse Discharge

Abstract

Power sources of implantable cardioverter-defibrillators (ICD) require high energy density to ensure longevity and sufficient rate capability to provide high power pulses for treating abnormal heart rhythms. Such demands have led to the design of Li/CFx-SVO battery, which leverages the excellent energy density of carbon monofluoride (CFx) and power density of silver vanadium oxide (SVO) through the use of a CFx-SVO hybrid cathode. A phenomenological model based on porous electrode theory was previously developed for Li/CFx-SVO, but it overlooked phase separation in SVO, Li+ diffusion limitations in particles, and reaction heterogeneity across particles. It was thus unable to accurately predict the voltage over-recovery behavior during transitions from medium to low currents, capture relaxation behavior after high current pulses without the use of unrealistically large capacitance values, or interactions between active materials in the hybrid electrode.In this work, we present a computational model of Li/CFx-SVO battery based on Multiphase Porous Electrode Theory for hybrid electrodes (Hybrid-MPET). Hybrid-MPET framework allows us to model the phase separation during reduction of SVO, concentration gradients in SVO particles and the evolution of reaction heterogeneities across an ensemble of particles under different current rates. As a result, our Hybrid-MPET model excels at predicting voltage-capacity behavior under constant current or constant load discharge, is capable of providing physical explanation of voltage over-recovery and voltage relaxation, and captures the interactions between SVO and CFx particles during transient currents. The Hybrid-MPET models are validated against experimental data from Li/CFx-SVO batteries of different designs, and show consistent modelling capability across different electrode thickness, particle lengthscales, and discharge timescales. Our work demonstrates how physics-based models can help provide fundamental understanding of experimental phenomenon, and we further discuss how the Hybrid-MPET framework could open up new opportunities to study the performance of hybrid electrode batteries and support their engineering design in a broader range of devices. Figure 1