Stress delocalization by grain boundaries densified in microsized alloying particles for advanced sodium storage

Microsized alloying anodes are the next practical step in achieving advanced batteries with higher energy density, yet the major challenge, associated with their alloying processing, lies in electro-mechanical failure phenomena caused by stress concentration. Here, we develop a universal grain boundaries (GBs) strategy on microsized alloying anodes for sodium ion batteries. The densified GBs function as fast diffusion paths to promote more homogenous sodiation. They facilitate consistent sodiation kinetics by stress transportation and delocalization, leading to electrochemical attributes superior to reported nanosized anodes (microsized Bi as a model, 200.5 mAh/g@277.5C, 1043.1 mAh/cm³@40C, high tap density of ∼2.4 g/cm³). Furthermore, GBs also act as dislocation catchers and barriers, significantly altering the sodiation behavior and subsequent structural evolution, and giving rise to enhanced fracture resistance and cycling stability. This work provides the key insight into GB-associated effects in microsized anodes on electro-mechanical coupling process, essential for development of advanced batteries.