Heterogeneous interface design of bimetallic selenide nanoboxes enables stable sodium storage

Abstract

The exploitation of proper nanomaterials with embedded-conversion-alloy features is of great significance for accelerating the realization of Na-ion batteries (NIBs). In this work, a unique nanobox, constructed with a heterojunction bimetallic selenide core and carbon shell (SnSe₂/CoSe₂@C), is synthesized and investigated as an anode for NIBs. The porous and flexible carbon nanobox not only alleviates volume expansion and maintains the structural stability, but also improves the conductivity. Foremost, the heterojunction existing in the phase boundary improves the reaction kinetics and promotes the storage of sodium ions owing to electron rearrangement and lattice distortion. The sodium storage mechanism of reversible phase-transition and alloying is clarified by in situ XRD (X-ray powder diffraction). When used as the anode of NIBs, this material can deliver a good reversible capacity of 304 mA h g⁻¹ at 2.0 A g⁻¹ over 500 cycles (the first cycle efficiency is 77.63%) and excellent rate performance (455 mA h g⁻¹ at 0.1 A g⁻¹ and 371 mA h g⁻¹ at 5.0 A g⁻¹).