Rational design for enhanced mechanical and kinetic properties of SnSb-based yolk-shell heterostructure as long cycle-life, high-rate Na-ion battery anode

Abstract

Bimetallic SnSb has significantly attracted attention as a Na-ion battery (SIB) anode owing to its higher theoretical capacity of 752 mA h g-1 compared to conventional hard carbon anodes. However, practical applications are hindered by substantial volume changes during sodiation/desodiation. Herein, a SnSb-based heterostructured anode (SnSb@C-SiOC) with high SnSb content (similar to 85%) is developed via two-step pyrolysis using SnSbOx@polydopamine precursors dispersed in silicone oil. The resulting SnSb yolk nanoparticles, encapsulated within a multi-functional C-SiOC bi-layered shell, facilitate rapid Na-ion transport and provide effective volume buffering during cycling for efficient electrochemical reactions and enhanced structural integrity. Post-mortem analyses reveal reversible crystalline phase transformations of SnSb with uniform elemental distributions, demonstrating the effectiveness of bi-layered shells. With superior mechanical robustness of the heterostructure confirmed by nanoindentation, the SnSb@C-SiOC anode delivers a high capacity of 445.6 mA h g-1 after 250 cycles at 2 A g-1, retaining 87.9% of its initial capacity and greatly outperforming pure SnSb. Additionally, a full cell combining the anode with a Na3V2(PO4)3 cathode shows promising cycle and rate performances, suggesting potential for practical applications. This study presents a viable approach for developing durable and efficient anode materials to advance SIBs and provide next-generation energy storage systems.