Identification of the structural, electronic properties, and ionic diffusion kinetics of Na3Cr2(PO4)3 by first-principles calculations

Polyanionic Na super ionic conductors (NASICON) have attained great attention as cathode materials for Na ion batteries. In this study, we have comprehensively investigated the structural and electronic properties, as well as the ionic diffusion kinetics of Na3Cr2(PO4)3 using first-principles calculations based on the density functional theory. Our calculations have figured out the R3¯c- P3¯c1- R3¯c phase transformation of Na3Cr2(PO4)3 during desodiation. The material shows a semi-conductive property with a band gap of ~ 1.0 V, which has turned into metallic during the charging process. Comparing with other transition metal polyanionic materials, Na3Cr2(PO4)3 exhibits relatively higher working voltage of 3.65-4.7 V due to the redox couple of Cr4+/Cr3+. Na ions have migrated in a zig-zag pathway with small energy barriers fell in the range of 0.17–0.42 eV, which validates the good rate capability of this NASICON-type cathode material in Na ion batteries.