Homeostatic Solid Solution Reaction in Phosphate Cathode: Breaking High‐Voltage Barrier to Achieve High Energy Density and Long Life of Sodium‐Ion Batteries

Abstract

The stable phase transformation during electrochemical progress drives extensive research on vanadium‐based polyanions in sodium‐ion batteries (SIBs), especially Na3V2(PO4)3 (NVP). And the electron transfer between V3+/4+ redox couple in NVP could be generally achieved, owing to the confined crystal variation during battery service. However, the more favorable V4+/5+ redox couple is still in hard‐to‐access situation due to the high barrier and further bring about the corresponding inefficiency in energy densities. In this work, the multilevel redox in NVP frame (MLNP) alters reaction pathway to undergo homeostatic solid solution process and breaks the high barrier of V4+/5+ at high voltage, taking by progressive transition metal (V, Fe, Ti and Cr) redox couple. The diversified reaction paths across diffusion barriers could be realized by distinctive release/uptake of inactive Na1 site, confirmed by the calculations of density functional theory. Thereby its volume change is merely 1.73% during the multielectron‐transfer process (∼2.77 electrons). MLNP cathode could achieve an impressive energy density of 440 Wh kg−1, driving the leading development of MLNP among other NASICON structure SIBs. The integration of multiple redox couples with low strain modulates the reaction pathway effectively and will open a new avenue for fabricating high‐performance cathodes in SIBs.This article is protected by copyright. All rights reserved

Enhancing Kinetics in Sodium Super Ion Conductor Na3MnTi(PO4)3 through Microbe-Assisted and Structural Optimization

“…Na 3 V 2 (PO 4 ) 3 (NVP) is one of the widely reported NASICON structure materials, and its structure is constructed by [PO 4 ] tetrahedron and [VO 6 ] octahedron via corner-sharing oxygen to form basic “lantern-unit” [V 2 (PO 4 ) 3 ] and Na + occupied the lattice space. − Since NVP only possesses a two-electron reaction at moderate potential (3.4 V, vs Na + /Na), it shows a low energy density that cannot meet the demands of energy storage devices . Nowadays, many researchers have been devoted to substituting the rare and V elements with different multivalence transition metals to realize high-energy density. , Already many multi-transition metal NASICON materials, such as Na 2 VTi­(PO 4 ) 3 , , Na 3 VCr­(PO 4 ) 3 , , and Na 2 CrTi­(PO 4 ) 3 , have been reported. , Furthermore, more researchers prefer to use the Mn element to replace V in NVP due to its high redox potential and low cost. − In 2016, Goodenough groups introduced a new cathode Na 4 MnV­(PO 4 ) 3 (NMVP). The energy output of NMVP was increased due to the enhanced operating potential of Mn 2+/3+ at 3.6 V (vs Na + /Na).…”

Sodium-ion battery using a NASICON-type Na3V2(PO4)3 cathode: quantification of diffusive and capacitive Na+ charge storage

“…22 Thus, synthesis methods have an impact on the microstructure, which consequently impacts the electrochemical performance. 23–25 Generally, the Na + ion charge storage in the SIB occurs by diffusive intercalation/de-intercalation during charging/discharging. The Na + charge storage can also occur by means of capacitive storage.…”

Toward High Performance of Na4Fe3(PO4)2P2O7 Cathode via Constructing a Porous Structure for Sodium-Ion Batteries

“…Layered oxides, , polyanion compounds, , and Prussian blue/white analogues , have been declared suitable host materials for the reversible extraction/insertion of Na + . However, the poor cycle life caused by the irreversible phase transition of layered oxides and the challenges due to the safety and toxicity of Prussian blue/white analogues have limited their practical application in stationary energy storage. , The sodium super ionic conductor (NASICON)-structured polyanion compound with a robust framework and a 3D diffusion channel has an ultralong cycle life but a slightly low energy density and is a fascinating candidate for stationary energy storage. − …”