Electrochemical behaviors of CuS as a cathode material for lithium secondary batteries

Systematic studies of CuS as a cathode material for a Lithium rechargeable battery are performed in 1 M LiPF6/EC-2EMC electrolyte. CuS undergoes a two-step reaction during the first discharge to 1.5 V with a capacity of 530 mAh(-1) g. The voltage profile and X-ray diffraction (XRD) patterns of the discharge reactions show the formation of LiXCuS during the first voltage plateau, and Cu1.96S, Li2S and metallic Cu during the second voltage plateau. The second plateau reactions are highly irreversible with partial dissolution of Li2S in the electrolyte which causes poor cycleability. The cycleability can be much improved by limiting the potential window between 2.6 and 1.8 V. The capacity is maintained of more than 70% of the initial value over 60 cycles with a cycle efficiency of 99%. (C) 2002 Elsevier Science B.V. All rights reserved.