V Doping in NASICON‐Structured Na₃MnTi(PO₄)₃ Enables High‐Energy and Stable Sodium Storage

Abstract

NASICON‐structured Na3MnTi(PO4)3 represents an appealing cathode for sodium storage. However, the low potential from Ti3+/4+ redox pair (≈2.1 V versus Na+/Na), undesirable rate capability, and unfavorable cyclability have inhibited its practical application. Herein, this study designs a Na3.1MnTi0.9V0.1(PO4)3 (NMTVP) cathode material by doping V into the Na3MnTi(PO4)3. The V substitution not only increases the medium discharge voltage, but also increases the capacity. The as‐prepared NMTVP demonstrates a four‐step redox reaction from the redox couples of V5+/4+ (≈4.1 V), Mn4+/3+ (≈4.0 V), Mn3+/2+ (≈3.6 V), and V4+/3+ (3.4 V). The NMTVP delivers a high capacity (118.5 mAh g−1 at 0.1 C), a high medium discharge voltage (3.53 V), a decent energy density (422 Wh kg−1), and an ideal cyclability (86% retention after 4500 cycles at 5 C). In situ X‐ray diffraction (XRD) uncovers the reversible structural evolution between Na3.1MnTi0.9V0.1(PO4)3 and Na0.9MnTi0.9V0.1(PO4)3 phases. The assembled NMTVP//hard carbon (HC) full cell also delivers a high capacity, a high operating voltage, and a good cyclability. This contribution offers new insights into the design of high‐energy NASICON‐structured cathode materials.

A NASICON-type Na3.67Cu0.17Fe0.5V1.33(PO4)3 cathode with multi-electron reaction for high-energy sodium-ion battery

“…Based on a first discharge capacity of 160 mA h g −1 and an average discharge potential of 2.8 V, the energy density of NCFVP reaches ∼450 W h kg −1 , which exceeds most phosphate/pyrophosphate-based SIB cathode materials. 10,32,41–47…”

A zero-strain Na-deficient NASICON-type Na2.8Mn0.4V1.0Ti0.6(PO4)3 cathode for wide-temperature rechargeable Na-ion batteries

“…3j. Compared to state-of-the-art Mn-based cathodes, 15,57–62 the current Na-deficient material presents a competitive energy density and remarkable cycling stability with a decent production cost, as seen in Fig. 3k, l and Table S7 †…”

Structurally Modulated Na4–xFe3–xVx(PO4)2P2O7 by Vanadium Doping for Long-Life Sodium-Ion Batteries

“…The low cost, high stability, and wide distribution of feedstock costs offered by sodium-ion batteries (SIBs) make them well-suited for fulfilling the demands of large-scale electrochemical energy storage systems. − However, SIBs still have great challenges; despite having the same working principle as lithium-ion batteries (LIBs), they are limited by the ionic radius (Na + : 1.02 Å; Li + : 0.76 Å), which leads to poor de-embedding capability. Therefore, there is a need to develop more suitable electrode materials to fulfill large-scale storage requirements. − In recent years, there has been a progression in sodium-ion cathode materials, with the emergence of various materials including transition-metal oxides, − polyanion materials, − and Prussian analogues. − Iron-based polyanion materials with low raw material cost, high thermal stability, and environmental friendliness have gained a lot of attention for their advantages. − Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP, theoretical capacity: 129 mA h g –1 ) was connected by combining [PO 4 ] and [P 2 O 7 ] groups with [FeO 6 ] octahedra, based on the redox Fe 2+ /Fe 3+ (average working voltage: 3.1 V), to realize the de-embedding of Na + in the cathode. Kim et al reported NFPP as a sodium-ion cathode material with a high reversible capacity of 113.5 mA h g –1 , marking the first discovery of such quality.…”