Molecular precursor-mediated facile synthesis of phase pure metal-rich digenite (Cu1.8S) nanocrystals: an efficient anode for lithium-ion batteries

Abstract

Copper sulfides have gained significant attention as alternative electrodes for rechargeable batteries. A simple and easily scalable synthetic pathway to access these materials is highly desirable. This paper describes the facile synthesis of metal-rich digenite Cu_1.8S nanocrystals from a structurally characterized new single-source molecular precursor in various high boiling solvents of varied polarity. The as-prepared nanostructures were thoroughly characterized by PXRD, Raman spectroscopy, EDS, XPS, electron microscopy techniques and diffuse reflectance spectroscopy to understand the crystal structure, phase purity, elemental composition, morphology and band gap. It was found that the reaction solvent has a profound role on their crystallite size, morphology and band gap, however the crystal structure and phase purity remained unaffected. Pristine Cu_1.8S nanostructures have been employed as an anode material in lithium-ion batteries (LIBs). The cell delivers a high initial charge capacity of ∼462 mA h g⁻¹ and retains a capacity of 240 mA h g⁻¹ even after 300 cycles at 0.1 A g⁻¹. DFT calculations revealed that multi-size polyhedron layers in the direction perpendicular to the two Li movement channels aid in the sustainable uptake of Li atoms with controlled volume expansion. The structure-mediated flexibility of the metal-rich Cu_1.8S lattice during lithiation permits high cyclability with reasonable retention of capacity.