Novel NASICON-typed porous Ni1.5V2(PO4)3/C and Mn1.5V2(PO4)3/C as anode materials for lithium-ion batteries: Crystal structure and electrochemical lithiation/delithiation reaction mechanism

Novel porous NaSICon-typed phosphate materials Ni1.5V2(PO4)3/C (NVP/C) and Mn1.5V2(PO4)3/C (MVP/C) are introduced as anode materials for Li-ion batteries. The materials were prepared via sol-gel method with annealing under argon flow. The structural, morphological, and electrochemical investigations of the materials as anodes for Li-ion batteries were conducted. The samples crystallized in a distorted triclinic system with a P1 space group. The two synthesized anode materials exhibited a conversion mechanism, displaying reversible initial charge capacities of 495 mAh.g- 1 and 550 mAh.g- 1 at 0.2C rate for NVP/C and MVP/C, respectively. Both materials showed better cycling stability at high rates and good rate capability performances with high coulombic efficiencies. For long term cycling, the materials can maintain a good reversible capacity for 1000 cycles, although a continuous decrease was noticed during the first cycles. The structural changes and the SEI growth impacting the electrochemical performances of the materials were evidenced via in operando XRD and X-ray photoelectron spectroscopy, leading to the understanding of the lithiation/delithiation reaction mechanism involved in the studied phosphates.