Localized anisotropic stress in the sodiation of antimony anode

Abstract

Although electrode degradation and failure in secondary batteries are hypothesized to stem from the localized chemo-electro-mechanical stress buildup during the charge-discharge process, the exact mechanism of stress generation is poorly understood. We quantitively resolve the stress accumulation in the Sb thin film anode during its gradual phase transitions in the sodiation/desodiation process by combining real-time electro-mechanical and electrochemical measurements with structural information further confirmed by spectroscopic methodologies. In the Sb thin films with (012) planes nearly normal to the surface, ~63% of the total interfacial stress (43.1 N m−1) is accumulated within the first 1/6 of the sodiation process of Na0.5Sb formation with Na-ions inserted between (012) planes. Only a small stress of 4.3 N m−1 is observed in the second 1/6 of the sodiation process due to preferential amorphization and solid solution formation. The last 2/3 of the sodiation process, where NaSb is converted into Na3Sb, generates only 1/3 of total stress (21.2 N m−1) because of the limited in-plane expansion. We also demonstrate that creating buffering voids can greatly reduce stress accumulation, especially during the early stage of the sodiation. The chemo-electro-mechanical insights from this work could serve as quantitative guidelines for the design and optimization of long-lasting Sb anode.