Boosting the operation stability of sodium-rich vanadium manganese-based NASICON phosphate as a cathode material for Na-ion batteries by Zn pinning effect

Abstract

Recently, NASICON-type Na4VMn(PO4)3, as a promising cathode material for sodium-ion batteries (SIBs), has received widespread attention owing to its high working voltage, high theoretical capacity, and fast Na+ migration kinetics. Unfortunately, serious structural deformation issue, caused by the Jahn-Teller effect of Mn3+, is still inevitable during repetitive charge/discharge processes, resulting in fast capacity fade. Therefore, designing a stable structure is crucial for developing practical vanadium manganese-based NASICON-type electrode materials. Herein, Zn2+-doped NASICON-type Na4VMn1−xZnx(PO4)3 can reduce Jahn-Teller effect of Mn3+ and expand the migration pathways of mobile Na+ ions. When being used as cathode materials for SIBs, Na4VMn0.9Zn0.1(PO4)3/C can provide 77.6% capacity retention at 1100 mA g−1 after the 500th cycle, which is much higher than that (67.6%) of Zn-undoped Na4VMn(PO4)3/C. Moreover, the reversible reactions of Mn3+/Mn2+ and V4+/V3+ redox couples are validated by ex-situ Powder X-ray diffraction (XRD) analyses of electrode materials cycled at different charge and discharge voltages. The fast reaction kinetics of the Na4VMn0.9Zn0.1(PO4)3/C electrode is confirmed via Galvanostatic intermittent titration technique (GITT). This research work offers an effective approach for devising high operation stability NASICON-type cathode materials for SIBs by pinning effect.