Insights into the Electrochemical Reaction Mechanism of a Novel Cathode Material CuNi2(PO4)2/C for Li-Ion Batteries.

In this work, we first report the composite of CuNi2(PO4)2/C (CNP/C) can be employed as the high-capacity conversion-type cathode material for rechargeable Li-ion batteries (LIBs), delivering a reversible capacity as high as 306 mA h g-1 at a current density of 20 mA g-1. Furthermore, CNP/C also presents good rate performance and reasonable cycling stability based on a nontraditional conversion reaction mode. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) characterizations show that CNP is reduced to form Cu/Ni and Li3PO4 during the discharging process, which is reversed in the following charging process, demonstrating that a reversible conversion reaction mechanism occurs. X-ray absorption spectroscopy (XAS) discloses that Ni2+/Ni0 exhibits a better reversibility compared to Cu2+/Cu during the conversion reaction process, while Cu0 is more difficult to be reoxidized during the recharge process, leading to capacity loss as a consequence. The fundamental understanding obtained in this work provides some important clues to explore the high-capacity conversion-type cathode materials for rechargeable LIBs.