Engineering 3D Well-Interconnected Na₄MnV(PO₄)₃ Facilitates Ultrafast and Ultrastable Sodium Storage

Na₄MnV(PO₄)₃ (denoted as NMVP) has drawn increasing attention owing to the three-dimensional framework and high theoretical capacity. Nevertheless, the inherent low electronic conductivity of NMVP impedes the scale-up commercial applications. In this work, the feasibility to achieve ultrahigh-rate capability and long lifespan by in situ embedding the intertwined carbon nanotube (CNT) matrix into the bulk of Na₄MnV(PO₄)₃@C composites through a facile wet-chemical approach is reported. The elaborately prepared Na₄MnV(PO₄)₃@C@CNTs cathode delivers a discharge capacity of 109.9 mA h g^-1 at C/5 with an impressive rate capability of 68.9 mA h g^-1 at an ultrahigh current rate of 90 C as well as a fascinating cycling performance of 68.3% capacity retention at 40 C after 4000 cycles. The optimum design of the 3D well-interconnected NMVP permitting fast kinetics for transported Na⁺/e^- is beneficial to the excellent electrochemical performance, which is further studied by the galvanostatic intermittent titration technique, cyclic voltammetry, and electrochemical impedance spectra measurements. The pseudocapacitance contributions are also investigated. The research demonstrates that the dual-nanocarbon synergistically modified NMVP composite is expected to facilitate the commercialization of sodium-ion batteries.