SnSe2 Quantum Dot/rGO composite as high performing lithium anode

Abstract

There have been limited applications in Tin Selenide based anode materials for lithium ion batteries due to low capacities from the alloying process (SnSe: 596mAhg−1, SnSe2: 426mAhg−1). This is mainly due to the significant loss of capacity during initial conversion process with the formation of Li2Se; a process that is considered irreversible in Tin based (SnXn, X = O, S, Se, n = 1 or 2) anode materials. Herein, ultra-fine Quantum Dots (QDs) of SnSe2 were designed to be embedded in a 3D matrix of rGO to release Sn nanoparticles that are able to catalyze the decomposition Li2Se and drive the conversion of Sn to SnSe2. In this manner, both conversion and alloying reactions can be utilized that greatly increases the effective capacity of SnSe2 anode. Through facile solvothermal synthesis followed by freeze-drying and thermal annealing, the rationally designed SnSe2 QDs/rGO effectively promoted reversible conversion of Sn to SnSe2. As a result, the nanocomposite exhibited enhanced capacities (778.5mAhg−1 at current density of 50mAg−1) that are beyond its theoretical values. The designed nanostructure also endowed the nanocomposite with high rate capabilities (324.5mAhg−1 at current density of 5000mAg−1) and ultra-long cycle life (92.2% capacity retention after 3000 cycles at 2000mAg−1). Post cycling analysis through ex situ TEM and XRD, coupled with electrochemical studies, were carried out to verify the reversible conversion reactions in SnSe2 QDs/rGO. The successful utilization of both conversion and alloying reactions in SnSe2 enables Tin Selenides to be on par with its oxide and sulfide analogues and hence a potential anode towards high energy density lithium ion batteries.