Boron Substituted NaV(P B O) Cathode Materials with Enhanced Performance for Sodium-Ion Batteries.

The development of excellent performance of Na-ion batteries remains great challenge owing to the poor stability and sluggish kinetics of cathode materials. Herein, B substituted NaVP B O (0 ≤ ≤ 1) as stable cathode materials for Na-ion battery is presented. A combined experimental and theoretical investigations on NaVP B O (0 ≤ ≤ 1) are undertaken to reveal the evolution of crystal and electronic structures and Na storage properties associated with various concentration of B. X-ray diffraction results indicate that the crystal structure of NaVP B O (0 ≤ ≤ 1/3) consisted of rhombohedral NaV(PO) with tiny shrinkage of crystal lattice. X-ray absorption spectra and the calculated crystal structures all suggest that the detailed local structural distortion of substituted materials originates from the slight reduction of V-O distances. NaVPBO significantly enhances the structural stability and electrochemical performance, giving remarkable enhanced capacity of 100 and 70 mAh g when the C-rate increases to 5 C and 10 C. Spin-polarized density functional theory (DFT) calculation reveals that, as compared with the pristine NaV(PO), the superior electrochemical performance of the substituted materials can be attributed to the emergence of new boundary states near the band gap, lower Na diffusion energy barriers, and higher structure stability.