Synthesis and electrochemical characterization of stoichiometric Cu2S as cathode material with high rate capability for rechargeable lithium batteries

Abstract

Abstract Synthesis of stoichiometric copper sulfide (Cu 2 S) was studied by spray pyrolysis (SP) with heat treatment for different Cu/S molar ratios in the starting solution and different synthesis and annealing temperatures. The sample prepared via SP at 400 °C and then annealed at 460 °C for 2 h showed the stoichiometric Cu/S ratio, which was verified by inductively coupled plasma-optical emission spectroscopy. The X-ray diffraction (XRD) peaks of the sample were indexed to the monoclinic structure with space group P 2 1 / c . The electrochemical performance of the stoichiometric Cu 2 S electrode was investigated by a cycle test and differential capacity analysis. The Cu 2 S electrode coated on an Al foil exhibited a first discharge capacity of 335 mAh g −1 at a charge-discharge rate of 0.1 C, which corresponds to 99.4% of its theoretical capacity. However it showed poor reversibility owing to the corrosion of Al foil by Cu. In contrast, the Cu 2 S electrode coated on Cu foil demonstrated stable cyclability at high charge-discharge rates of up to 30 C. Exsitu XRD analysis showed that a phase transformation from the monoclinic Cu 2 S structure with the space group P 2 1 / c to the tetragonal Cu 1.96 S structure with the space group P 4 3 2 1 2 gradually progressed during the initial five cycles.