Regulating Bond Structure in Polyanion Cathode for Long-Cycle-Life Sodium-Ion Batteries

Abstract

The NASICON-type Na₄MnV(PO₄)₃ (NMVP) cathode is a potential candidate for sodium-ion batteries (SIBs) due to its intrinsic safety and cost advantages. However, its performance is limited by intrinsic low electronic conductivity and Jahn–Teller distortion of Mn. In this study, Co is substituted at the Mn site to take advantage of the stronger polarization effect of Co²⁺ and the ionic radius difference, which shortens the Mn–O bond length and strengthens its bonding, stabilizing the MnO₆ octahedral structure. Furthermore, Co doping lowers the Na⁺ migration energy barrier and facilitates more efficient Na⁺ transport. Therefore, the prepared NMCVP-0.05 sample exhibits a stable cycling performance (retaining 88.9% after 3800 cycles at 10 C) and rate performance (71.7 mAh g^–1 at 50 C). This work reveals the mechanism by which regulating the bond structure in NMVP affects sodium storage performance and proposes a stability-enhancing strategy for Mn-based polyanionic cathodes.