High Young's modulus NaF coating on bulk Sn: mechanical confinement effect drives durable sodium storage by alleviating (de)sodiation stress

Sn has emerged as a promising anode material for next-generation sodium-ion batteries (SIBs) owing to its high theoretical capacity. However, the high volumetric expansion of Sn anode upon sodiation generates significant internal stress, which leads to particle cracking, pulverization and electrode failure. Herein, we report a novel and facile approach to in situ coat a sodium fluoride (NaF) layer on bulk Sn particles via a solution supersaturation route. The high Young's modulus of the NaF coating enables a strong mechanical confinement effect, which effectively suppresses the volume expansion and mechanical stress of Sn. Additionally, the NaF coating promotes the formation of a thin, uniform and dense solid electrolyte interphase film, thereby resulting in a significantly improved Coulombic efficiency. The designed Sn@NaF anode exhibits remarkable cycling stability and low-temperature adaptability in both half cell and full cell. These results highlight the great potential of the Sn@NaF anode for high-energy-density SIBs.