A Phase-Transition-Free Sodium Vanadium Phosphate Cathode via Medium-Entropy Engineering for Superior Sodium Ion Batteries.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 39815152.
- Also identified by DOI 10.1002/adma.202414358.
- No licence information is recorded for this record.
- Because redistribution is not established, this page shows the abstract only. Follow the links below for the full text.
Abstract
Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>, based on multi-electron reactions between V<sup>3+</sup>/V<sup>4+</sup>/V<sup>5+</sup>, is a promising cathode material for SIBs. However, its practical application is hampered by the inferior conductivity, large barrier of V<sup>4+</sup>/V<sup>5+</sup>, and stepwise phase transition. Herein, these issues are addressed by constructing a medium-entropy material (Na<sub>3.2</sub>V<sub>1.1</sub>Ti<sub>0.2</sub>Al<sub>0.2</sub>Cr<sub>0.2</sub>Mn<sub>0.2</sub>Ni<sub>0.1</sub>(PO<sub>4</sub>)<sub>3</sub>, ME-NVP) with strong ME─O bond and highly occupied Na2 sites. Benefiting from the medium-entropy effect, ME-NVP manifests a phase-transition-free reaction mechanism, two reversible plateaus at 3.4 (V<sup>3+</sup>/V<sup>4+</sup>) and 4.0 V (V<sup>4+</sup>/V<sup>5+</sup>), and small volume change (2%) during Na<sup>+</sup> insertion/extraction processes, as confirmed by comprehensive in/ex situ characterizations. Moreover, kinetics analysis illuminates the superior Na<sup>+</sup> diffusion ability of ME-NVP. Thus, the ME-NVP cathode realizes remarkable rate capability of 67 mA h g<sup>-1</sup> at 50C and a long-term lifespan over 10 000 cycles (capacity retention of 81.3%). Theoretical calculations further illustrate that the weak binding of Na<sup>+</sup> ion in the channel is responsible for the rapid Na<sup>+</sup> diffusion, accounting for the superior reaction kinetics. Moreover, rigid MEO<sub>6</sub> octahedral and feasible rearrangement of Na<sup>+</sup> ions can suppress the phase transition, thus endowing an ultrastable ME-NVP cathode. This work highlights the significant role of medium-entropy engineering in advancing the output voltage, cycling stability, and rate capability of polyanionic cathodes.