Scalable structural refining via altering working pressure and in-situ electrochemically-driven Cu-Sb alloying of magnetron sputtered Sb anode in sodium ion batteries

Abstract Sb is a promising anode for sodium ion batteries (SIBs) but held back from practical application owing to its pulverization induced by dramatic volumetric variation. Herein, we propose a simple pressure-induced regulation strategy to efficiently refine nanoscale column-channel architecture of Sb layer by magnetron sputtering, which is easily manipulated and reproductive in practical conditions. The refining process under high working pressure can be ascribed to the synergistic effects from the shadow effect, the low kinetic energy of sputtered Sb atoms and high diffusion barrier on substrate. As benchmarked with Sb@0.2Pa and Sb@1Pa electrodes, the Sb@3Pa anode exhibits significantly enhanced electrochemical performance owing to structural refining effect generated by the elevated working pressure, effectively accelerating the ion/electron transfer and mitigating the volumetric variations. Notably, the progressive in-situ electrochemically-driven alloying in Sb layer on the Cu substrate to form CuxSb with the gradient Cu/Sb content is detected and further rationalized by operando XRD, ex-situ SEM and DFT calculations. Simultaneously, the formed Cu-Sb layer yields a novel (de)sodiation mechanism of CuxSb1-x ↔ NayCuxSb1-x ↔ Na3CuxSb1-x after the 1st discharge.