Topotactic Syntopogenous Sodium Vanadium Fluoride for High-Performance Sodium-Ion Batteries: Electron and Sodium-Ion Reservoirs in Perovskite/Diperovskite Superlattice
Ying Guo, Kai Li, Yun Gong, Jianhua Lin
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 3 VF 6 /NaVF 3 superlattice formulated as Na 2.9 V 1.1 F 6 (NVF) was synthesized by a facile one-step low-temperature hydrothermal reaction. NVF nanoparticles show an excellent Na + storage capacity (∼205 mAh g –1 ) 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 3 VF 6 with better electron conductivity acts as a Na + reservoir for effective electron transfer. Highly reversible (de)intercalation of Na + is achieved in the channel of perovskite-type NaVF 3 with structural integrity.