A facile synthesis of copper sulfides composite with lithium-storage properties

• Copper sulfides can be simply synthesized by heating a mixture of copper and sulfur powders in different stoichiometries.
• The copper-excess copper sulfides electrodes show enhanced electrochemical performance.
• The critical factor for CuxS electrodes achieving high performance is that the ratio of Cu and S is greater than 2.

Copper sulfides are synthesized by heating a mixture of copper and sulfur powders in different stoichiometries in N-methyl-2-pyrrolidinone (NMP) solvent. All the electrodes show excellent electrochemical performance, especially ‘copper excess’ copper sulfides electrodes. These electrodes can be charged and discharged at high rate, with good capacity retention. The electrochemical reaction mechanism of copper sulfides during discharge–charge process is investigated. It is most likely that all of S element in the copper excess electrode would transfer into a crystal of Cu2S during charge–discharge cycles, which corresponded to a single electrochemical reaction and showed excellent cycling and rate performance. These encouraging results indicate that copper-excess copper sulfides could be a promising anode material for lithium batteries with high rate capability.