Microsized alloying particles with engineered eutectic phase boundaries enable fast charging and durable sodium storage

Microsized alloying particles have broad application prospects as anodes of high energy density batteries, but their fast charging and long cyclic stability are seriously affected by the sluggish bulk diffusivity, poor stress response and uncontrolled electrode/electrolyte interface. Herein, we develop a microsized Bi-Sn alloying particle model system with the engineered eutectic phase boundaries (PBs) that provide high energy density, fast charging capability, and long cyclic stability for sodium ion batteries (SIBs). PBs with spacious atomic misalignment can effectively promote the bulk diffusivity, which facilitates the fast ion diffusion. The asynchronous multi-step alloying mechanism induced by PBs can not only maintain the permanent alloying driving force of particles by releasing stress, but also improve the mechanical robustness and interface stability of particles by changing the process of structure evolution. The Bi6Sn4 anode delivers a fast charging capability of 407 mAh g⁻¹ at 8 A g⁻¹ (20C), comparable even to the reported nano-sized alloy anodes. The electrode can also achieve a high tap density of 2.1 g cm⁻³ and a volumetric capacity of 1226 mAh cm⁻³, indicating a practical potential. The present results offer insights into the fast charging and durability for high energy SIBs by PBs engineering of microsized alloying particles.