Elucidating the Impact of Mg Substitution on the Properties of NASICON‐Na_3+yV_2−yMg_y(PO₄)₃ Cathodes

Abstract

Vanadium multi-redox based NASICON-Na z V 2-y M y (PO 4 ) 3 (3 ≤ z ≤ 4; M = Al 3+ , Cr 3+ and Mn 2+ ) cathodes are particularly attractive for Na-ion battery applications due to their high Na insertion voltage (>3.5 V vs. Na + /Na 0 ), reversible storage capacity (~150 mA h g -1 ) and rate performance. However, their practical application is hindered by rapid capacity fade due to bulk structural rearrangements at high potentials involving complex redox and local structural changes. To decouple these factors, we have studied a series of Mg 2+ substituted Na 3+y V 2y Mg y (PO 4 ) 3 (0 ≤ y ≤ 1) cathodes for which the only redox-active species is vanadium. Whilst X-ray diffraction (XRD) confirms the formation of solid solutions between the y = 0 and 1 end members, X-ray absorption spectroscopy and solid-state nuclear magnetic resonance reveal a complex evolution of the local structure upon progressive Mg 2+ substitution for V 3+ . Concurrently, the intercalation voltage rises from 3.35 to 3.45 V, due to increasingly more ionic V-O bonds, and the sodium (de)intercalation mechanism transitions from a two-phase for y ≤ 0.5 to a solid solution process for y ≥ 0.5, as confirmed by inoperando XRD, whilst Na-ion diffusion kinetics follow a non-linear trend across the compositional series.

Substituting inert phosphate with redox-active silicate towards advanced polyanion-type cathode materials for sodium-ion batteries

“…It is noted that the average discharge voltage of an NVP-Si cathode was ∼3.36 V, 50 mV higher than that of pristine NVP. Remarkably, both the power density and energy density of as-assembled Na||NVP cells are higher than those values for most reported NVP materials in recent publications [42][43][44][45][46][47] (Fig. 2b).…”

Promising anode materials for alkali metal ion batteries: a case study on cobalt anti-MXenes

“…16 To further improve the energy densities of these ''alkali metal ion batteries'' (alkali metal = Li, Na, and K), novel electrode and electrolyte materials need to be discovered. 17,18 Previous research showed that layered materials could be promising anode candidates for alkali metal ion batteries (AMIBs). [19][20][21][22] These layered materials are composed of stacks of novel 2D materials like graphene, borophene, phosphorene, transition metal dichalcogenides (TMDs), transition metal carbides, and carbonitrides (MXenes), or their hybrids.…”

“…16 To further improve the energy densities of these “alkali metal ion batteries” (alkali metal = Li, Na, and K), novel electrode and electrolyte materials need to be discovered. 17,18…”

Promising anode materials for alkali metal ion batteries: A case study on cobalt anti-MXenes

“…16 To further improve the energy densities of these "alkali metal ion batteries" (alkali metal = Li, Na, and K), novel electrode and electrolyte materials need to be discovered. 17,18 Earlier research showed that layered materials could be promising anode candidates for alkali metal ion batteries (AMIBs). [19][20][21][22] These layered materials are composed of stacks of novel 2D materials like graphene, borophene, phosphorene, transition metal dichalcogenides (TMDs), transition metal carbides, and carbonitrides (MXenes), or their hybrids.…”