Stabilization of the Solid-Electrolyte-Interphase Layer and Improvement of the Performance of Silicon-Graphite Anodes by Nanometer-Thick Atomic-Layer-Deposited ZnO Films

Silicon (Si) is a promising anode material due to its high theoretical capacity and abundant presence as the second most common element in the earth's crust. However, the formation of an unstable solid-electrolyte interphase (SEI) and significant volume expansion during lithiation result in structural degradation, leading to a decrease in the cycle life for Si-based anodes. This paper reports on the electrochemical performance of the silicon/graphite (Si/Gr) electrodes coated with nanometer-thick ZnO layers prepared by atomic layer deposition (ALD). In our study, ZnO layers were deposited using 5-40 ALD cycles on Si/Gr electrodes of similar to 20 mu m thickness. Electrochemical measurements such as galvanostatic charging/discharging at different C-rates and electrochemical impedance spectroscopy were performed utilizing the pristine and 5-40 ALD cycles of ZnO on Si/Gr electrodes in a half-cell configuration. The Si/Gr electrodes (pristine and ZnO-coated) were analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) before and after electrochemical cell cycling. The ZnO-coated samples showed a better electrochemical rate performance than the uncoated pristine Si/Gr sample. The reversible conversion of the ZnO ALD films was demonstrated through dQ/dV plots and XPS analysis during (de)lithiation. The ultrathin ZnO layers passivate the underlying Si/Gr electrodes, help in the formation of a stable SEI layer, and facilitate lithium-ion transport through the SEI layer.