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

A layered GeS 2 material was assessed as an electrode material in the fabrication of superior rechargeable Li-ion batteries. The electrochemical Li insertion/extraction behavior of the GeS 2 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 GeS 2 electrode, an interesting amorphous GeS 2 -based composite was developed and tested for use as a high-performance electrode. Interestingly, the amorphous GeS 2 -based composite electrode exhibited highly reversible discharging and charging reactions, which were attributed to a conversion/recombination reaction. The amorphous GeS 2 -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 GeS 2 and its amorphous GeS 2 /C composite are novel alternative anode materials for the potential mass production of rechargeable Li-ion batteries with excellent performance.