Synthesis, Characterization, Electrochemistry, and In Situ X‐ray Diffraction Investigation of Ni3(PO4)2 as a Negative Electrode Material for Lithium‐Ion Batteries

Abstract Nickel orthophosphate, Ni 3 (PO 4 ) 2 , was successfully synthesized using solid‐state reaction at 900 °C. The effect of the calcination temperature on the material purity was investigated at different temperatures (700–900 °C). XRD analysis has shown that Ni 3 (PO 4 ) 2 crystallizes in a monoclinic system with P 2 1 /a space group. The electrochemical performances of carbon‐coated Ni 3 (PO 4 ) 2 were investigated for the first time versus Li + /Li and improved by the optimization of the cut‐off voltage, the carbon‐coating source, and the binder used. The best performance was delivered when using 0.01 V cut‐off voltage, sucrose for C‐coating, and carboxymethyl cellulose (CMC) binder. A reversible capacity of 249 mAh g −1 and a capacity retention around 74–79 % after 90 cycles with a good coulombic efficiency of 98 % were obtained at C/5 current rate. In situ XRD measurements demonstrated the irreversible amorphization of the Ni 3 (PO 4 ) 2 crystal structure during the first discharge process, confirming that this phosphate exhibits a pure conversion mechanism.