Chemical Bonding in Multiple Encapsulation Geometry of Bi2se3-Based Conversion-Alloying Anode Materials for Superior Sodium-Ion Storage

Abstract

Conversion-alloying based material has regarded as one of the most valuable anode electrodes for low-cost sodium-ion batteries (SIBs), while the large volume variation and poor electrochemical kinetics behavior become the key scientific issues hindering the application. Herein, Bi2Se3 nanoflowers assembled by ultra-thin nanosheets, vertically anchored on reduced graphene oxide via strong chemical bonding of C-O-Bi and tightly wrapped by N-doped C nanolayer (Bi2Se3@rGO@NC), are constructed as anodes for Na-ion storage. The physicochemical encapsulation geometry is conductive to acquiring excellent electrode integrity by accommodating huge lattice strain, as well as boosting great dynamic process by dispelling band gap and decreasing Na-ion diffusion barrier. Na-ion insertion/extraction proceeds via conversion-alloying dual-mechanism with 12-electron transport per formula unit employing Bi-ion as redox site (Bi2Se3 + 12Na+ + 12e- ↔ 2Na3Bi +3Na2Se). Thus, high initial charge capacity of 288.4 mAh·g-1 at 50 mA·g-1, exceptional cycling stability with ultra-long lifespan over 1000 cycles and great rate property (119.9 mAh·g-1 at 5.0 A·g-1) can be achieved for Bi2Se3@rGO@NC. This work may open up systematic research on conversion-alloying anodes and shed insights into the illumination of electrochemical reaction mechanism for SIBs.

Keywords: sodium-ion batteries, Anode materials, bismuth selenide, chemical bonding, conversion-alloying mechanism