Topotactic Syntopogenous Sodium Vanadium Fluoride for High-Performance Sodium-Ion Batteries: Electron and Sodium-Ion Reservoirs in Perovskite/Diperovskite Superlattice.

Guo, Ying; Li, Kai; Gong, Yun; Lin, Jianhua · Nano Lett · 2024

basic_science · Level V

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Abstract

In order to simultaneously accelerate ion and electron transfer in sodium-ion battery (SIB) cathodes, a topotactic superlattice was utilized, in which the atomically intrinsic lattice-matching effect from inner to external surface can boost the charge transfer due to the disappearance of the heterojunction interface. Herein, a topotactic syntopogenous Na<sub>3</sub>VF<sub>6</sub>/NaVF<sub>3</sub> superlattice formulated as Na<sub>2.9</sub>V<sub>1.1</sub>F<sub>6</sub> (NVF) was synthesized by a facile one-step low-temperature hydrothermal reaction. NVF nanoparticles show an excellent Na<sup>+</sup> storage capacity (∼205 mAh g<sup>-1</sup>) in a high voltage window up to 4.2 V with ultralong cycling stability. That is associated with the mixed occupancy of V and Na in NVF. The multivalent V centers serve as electron reservoirs to inhibit phase transformation, and the Na-enriched Na<sub>3</sub>VF<sub>6</sub> with better electron conductivity acts as a Na<sup>+</sup> reservoir for effective electron transfer. Highly reversible (de)intercalation of Na<sup>+</sup> is achieved in the channel of perovskite-type NaVF<sub>3</sub> with structural integrity.