Electrochemical reactions of lithium with CuP2 and Li1.75Cu1.25P2 synthesized by ballmilling

Copper phosphide (CuP2) and lithium copper phosphide (Li1.75-Cu1.25P2) were synthesized by high-energy ballmilling at room temperature. The electrochemical reactions between lithium and these samples have been studied. The first lithium insertion into the CuP2 phase till 0.0 V vs. Li leads to copper reduction and the formation of lithium phosphide (Li3P), corresponding to a long voltage plateau. The subsequent lithium extraction until 1.3 V vs. Li presents three voltage plateaus related to the formation of new phases such as Li2CuP, giving a reversible capacity about 810 mAh/g and faradic yield about 61%. It means that both copper and phosphorus face a change of the oxidation state for the electrochemical insertion and extraction. Lithium copper phosphide exhibits a similar reaction process. However, it provides a reversible capacity of 750 mAh/g and faradic yield of 100% at the first cycle.