Insight into the effect of Nb5+ on the crystal structure and electrochemical performance of the Li-rich cathode materials

The density functional theory (DFT) and electronic structure around the Fermi level results show that the binding energy change of Nb-doped samples is much higher than that of the pristine sample. • Nb-doped Li-rich materials are synthesized via a modified one-step sol–gel and high-temperature calcination method. • Nb-doped Li-rich materials show outstanding electrochemical performance. • The electrochemical performance of Nb-doped Li-rich materials was interpreted by the density of states. The Nb-doped Li-rich materials Li 1.2 (Mn 0.54 Ni 0.13 Co 0.13 ) 1-x Nb x O 2 are synthesized via a modified one-step sol–gel and high-temperature calcination method. The crystal structure and surface morphology of synthesized materials are analyzed through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. After optimization, the Nb-0.02 sample exhibits exceptional electrochemical performance, that is, the initial discharge-specific capacity of 305.9 mAh g −1 at 0.08 C and 202.6 mAh g −1 at 1 C, respectively. Combined with the result of the density of states (DOS), we found that the doping of Nb 5+ into the crystal structure significantly reduces the value of the band gap of the Li 2 MnO 3 (1.07 eV). At the same time, the strengthened Nb–O bond and Nb 5+ with big ionic radius, regulate the degree of oxygen ion participation in the redox reaction and enhance the electrochemical performance of the Li-rich materials.