Solvothermal synthesis of pyrite FeS₂ nanocubes and their superior high rate lithium storage properties

Iron pyrite nanocubes with particle sizes of around 80-120 nm have been synthesized via a facile solvothermal method. Time-dependent characterization found that the iron(ii) chloride and sulfur precursors first react to form sheet-like amorphous Fe_1-xS, which transforms into pyrite FeS₂ nanocubes upon further heating. As an anode material for lithium ion batteries, the as-synthesized pyrite FeS₂ nanocubes were found to deliver a reversible discharge capacity of 540 mA h g^-1 after cycling for 150 cycles at a current density of 1 A g^-1. Even at higher current density of 5 A g^-1, the pyrite FeS₂ electrode still managed to give a stable discharge capacity of about 220 mA h g^-1. The enhanced lithium storage properties are attributed to its higher specific surface area that can provide more lithium ion (Li⁺) reaction sites, leading to less polarization and better cycling performance.