Highly Reversible and Superior Li-Storage Characteristics of Layered GeS₂ and Its Amorphous Composites

A layered GeS₂ material was assessed as an electrode material in the fabrication of superior rechargeable Li-ion batteries. The electrochemical Li insertion/extraction behavior of the GeS₂ electrode was investigated from extended X-ray absorption measurements as well as by cyclic voltammetry and differential capacity plots to better understand its Li insertion/extraction behavior. Using the Li insertion/extraction reaction mechanism of the GeS₂ electrode, an interesting amorphous GeS₂-based composite was developed and tested for use as a high-performance electrode. Interestingly, the amorphous GeS₂-based composite electrode exhibited highly reversible discharging and charging reactions, which were attributed to a conversion/recombination reaction. The amorphous GeS₂-based composite electrode exhibited highly reversible and outstanding electrochemical performances, a highly reversible capacity (first charge capacity: 1298 mAh g^-1) with a high first Coulombic efficiency (83.3%), rapid rate capability (ca. 800 mAh g^-1 at a high current rate of 700 mA g^-1), and long capacity retention over 180 cycles with high capacity (1100 mAh g^-1) thanks to its interesting electrochemical reaction mechanism. Overall, this layered GeS₂ and its amorphous GeS₂/C composite are novel alternative anode materials for the potential mass production of rechargeable Li-ion batteries with excellent performance.