Electrochemical Synthesis of Type I Na_8Si_(46) Clathrate with a Na B'-Alumina Solid Electrolyte

摘要

Intermetallic clathrates are a class of materials comprising face-sharing polyhedral cages of Tetrel (Si, Ge Sn) elements that encapsulate alkali or alkaline earth metal guest atoms. With their unique structures and tunable cage sizes, clathrates have received much interest for their thermoelectric, superconducting, optoelectronic, and electrochemical properties. Due to the large interest in Tetrel elements for Li-ion anodes, our group has been investigating the electrochemical properties of clathrates for Li-ion battery applications. We recently studied the guest free Type I clathrates (i.e. Si_(46)) with ab initio calculations and found that Li insertion is favorable into the empty cages and the migration barriers are very low (0.15-0.3 eV) suggesting possible applications as anodes. However, obtaining pure phase selection of the Si clathrates from the desodiation of the Na_4Si_4 Zintl phase has been difficult due to the lack of kinetic control during the reaction. To address this challenge, we demonstrate a proof-of-concept electrochemical cell which desodiates Na_4Si_4 at 450-550°C to phase selectively form the type I Na_8Si_(46) clathrate phase.