A composite electrode model for lithium-ion batteries with silicon/graphite negative electrodes

Abstract

Silicon is a promising negative electrode material with a high specific capacity, which is desirable for commercial lithium-ion batteries. It is often blended with graphite to form a composite anode to extend lifetime, however, the electrochemical interactions between silicon and graphite have not been fully investigated. Here, an electrochemical composite electrode model is developed and validated for lithium-ion batteries with a silicon/graphite anode. The continuum-level model can reproduce the voltage hysteresis and demonstrate the interactions between graphite and silicon. At high states-of-charge, graphite provides the majority of the reaction current density, however this rapidly switches to the silicon phase at deep depths-of-discharge due to the different open circuit voltage curves, mass fractions and exchange current densities. Furthermore, operation at high C-rates leads to heterogeneous current densities in the through-thickness direction, where peak reaction current densities for silicon can be found at the current collector–electrode side as opposed to the separator–electrode side for graphite. Increasing the mass fraction of silicon also highlights the beneficial impacts of reducing the peak reaction current densities. This work, therefore, gives insights into the effects of silicon additives, their coupled interactions and provides a platform to test different composite electrodes for better lithium-ion batteries.