Comparison of Silicon and Graphite Anodes: Temperature-Dependence of Impedance Characteristics and Rate Performance

A meaningful benchmarking of battery active materials with inherently different properties requires knowledge of both their intrinsic electrochemical properties as well as of the differences in the resulting porous electrode structures for equal, practically relevant areal capacities. Here we compare graphite and microsilicon anodes with practical areal capacities of 2.8 mAh cm⁻² for lithium-ion batteries with regard to their temperature-dependent kinetic charge-transfer resistances (R _ct) and their ion transport resistances through the electrolyte phase within the pores of the electrodes (R _ion), measured via impedance spectroscopy. We deconvolute the kinetic resistance from the impedance spectra by individually measuring the temperature-dependent pore resistance between −5 and +45 °C, showing that the charge-transfer resistance dominates at low temperatures, while at high temperatures the pore resistance dominates for both electrode types due to the significantly higher activation energy of R _ct. An analysis of the potential profile of the electrodes at different lithiation rates shows how the thinner silicon electrode is significantly less affected by R _ion-induced transport losses compared to a thicker graphite electrode, resulting in lower overpotentials when fast-charging at high temperatures, despite similar kinetic resistances. Overall the silicon electrodes could be charged up to two times faster than graphite before reaching 0 V vs Li⁺/Li.