Structurally controlled Na4VMn(PO4)3 cathodes via alkali metal cation substitution for high-performance sodium-ion batteries

The Na superionic conductor (NASICON)-type Na 4 VMn(PO 4 ) 3 (NVMP), with its three-dimensional framework and high operating voltage, has demonstrated great potential as a cathode material for Sodium-ion batteries (SIBs). However, its performance is hindered by the Jahn-Teller effect from Mn 3+ and slow Na + diffusion kinetics, leading to capacity fade and structural instability. In this study, Li + and K + cations were separately doped into the NVMP structure to improve electrochemical performance . Li-doping enhanced the V 3+ /V 4+ redox activity and significantly reduced the Jahn-Teller effect, contributing to a high-capacity retention of 97.7 % after 100 cycles at 1 C and 96.1 % after 1000 cycles at 10 C. This high-rate stability highlights the role of Li-doping in maintaining structural integrity and efficient ion transport under fast cycling conditions. Meanwhile, K-doping improved the structural stability by stabilizing V 3+ oxidation states, leading to a capacity retention of 110.3 mAh g −1 after 100 cycles at 1 C and a discharge capacity of 99 mAh g −1 at 10 C. X-ray photoelectron spectroscopy (XPS) further confirmed that both Li + and K + doping suppressed the Jahn-Teller effect by regulating the Mn 3+ environment, which contributed to the improved cycling stability and Na + cation diffusion kinetics. These findings highlight the effectiveness of alkali metal cations doping as a strategy to enhance the cycling performance of NVMP cathodes for high-performance SIBs.