Active Material Lithiation in Gr/SiOx Blend Anodes at Increased C-Rates

Abstract

The energy density of lithium-ion batteries can be improved by adding silicon as a secondary active anode material alongside graphite. However, accurate state estimation of batteries with blend electrodes requires detailed knowledge of the interplay between the active materials during lithiation. Challenges arise from the current split between the active materials and the overlap of their working potentials. This study examines the lithiation behavior of blend anodes using a setup consisting of a pure graphite and a pure SiOx half-cell connected in parallel. The setup allows for current measurements of both active materials, the determination of the state of lithiation throughout the entire charging process and measurements of balancing effects between the active materials during relaxation periods. Analysis of the behavior at increased charge rates results in greater SiOx lithiation after similar charge throughput indicating better kinetics for SiOx compared to graphite. A Doyle-Fuller-Newman model of a blend anode is used to further investigate the experimental findings on the lithiation behavior and transfer them to blend electrodes. Simulation-based variations of the silicon content show that an increased SiOx content in blend anodes leads to improved rate capability.