Orbital modulation to restrain anti-site defects in NASICON cathode for high-performance sodium-ion batteries

Abstract Sodium superionic conductor-type Na 3 MnTi(PO 4 ) 3 is a promising cathode for sodium-ion batteries. However, the anti-site defects due to the occupation of Na vacancies by Mn lead to voltage hysteresis and capacity loss. In this study, we present a method for efficient manipulating the e g orbital of elemental Mn in the Na 3 MnTi(PO 4 ) 3 to enhance the Mn–O covalent interaction. This modulation of the e g orbital facilitates the electron filling in the Mn (3 d – e g ) orbital and strengthens hybridization with the O (2 p ) orbital, which increases the formation energy of Mn defects and thereby effectively restrains anti-site defects in Na 3 MnTi(PO 4 ) 3 . The optimized Na 2.97 Li 0.03 MnTi(PO 4 ) 3 cathode delivers a capacity of 115.8 mAh g −1 at 10 C (164.9 mAh g −1 at 0.1 C), while retaining an outstanding capacity retention of 89.2% over 3000 cycles, along with stable cycling characteristics under temperatures ranging from −30 °C to 40 °C. The pouch-type full cell (50 × 35 × 5 mm 3 ) using the Na 2.97 Li 0.03 MnTi(PO 4 ) 3 cathode and hard carbon anode further demonstrates its promising application. This study elucidates the anti-site defects suppression mechanism through molecular orbital analysis, offering new perspectives for developing high-performance sodium-ion cathode materials.