High performance stoichiometric Cu₂S cathode on carbon fiber current collector for lithium batteries

In this study, stoichiometric Cu₂S with monoclinic crystal structure with space group P2₁/c was prepared via spray pyrolysis with followed heat treatment. Its electrochemical properties were investigated after coating on a carbon fiber paper (CFP) current collector and cycling at various cut-off voltages. The reversible stable capacity of about 330 mAh g⁻¹ (98% of its theoretical capacity) exhibited by the cell for 20 cycles at 0.1C and slightly dropped to 311 mAh g⁻¹ after 50 cycles. At higher 1C rate, a discharge capacity of 280 mAh g⁻¹ was retained for 100 cycles with approximately 100% Coulombic efficiency between 1.0-3.0 V. While the gradual capacity decrease is observed with the increase of the discharge cut-off voltage to avoid solid electrolyte interface (SEI) formation during the 1st discharge. The cells showed capacities of 307 and 280 mAh g⁻¹ after the 5th cycle at 0.1C when cycled between 1.1-3.0 V and 1.2-3.0 V, respectively, due to the lowered lithium ion diffusion. Ex situ XRD analysis of the recovered electrodes after cycling with near theoretical capacity allowed discussing the actual reaction mechanism of stoichiometric Cu₂S with Li⁺.