Microalloying induced stable welded interfaces for highly reversible zero-excess sodium metal batteries

Abstract

The noteworthy benefits of zero-excess sodium metal batteries (ZSMBs) regarding their energy density, sustainability, carbon footprint and cost make them a promising supplement or even substitute for lithium-ion batteries. Nevertheless, zero-excess sodium plating/stripping on an anode substrate encountered with sodium dendrite growth, inactive sodium generation and irreversible solid electrolyte interphase (SEI) formation make the improvement of the cycling stability of ZSMBs challenging. Herein, we discovered that structural instability and insufficient sodophilicity of the substrate interface are critical factors causing the irreversible sodium plating/stripping. Then, a microalloying welding strategy modified by nano-zinc coating was proposed to construct sodophilic interfaces and form a thin and robust organic/inorganic hybrid SEI in situ. This unique interface enables highly reversible sodium plating/stripping by improving the kinetic behavior of ion/electron exchange at the interface. Ultimately, ZSMBs assembled using this modified substrate with a highly loaded Na₃V₂(PO₄)₃ (NVP) cathode (∼10.4 mg cm⁻²) can deliver 90.5% initial coulombic efficiency and cycling stability for more than 800 times at an average decay rate of 0.041% per cycle. More importantly, the microalloying welding approach delineated in this study offers valuable insights into the attainment of a robust sodophilic interface. This study proposes that overcoming the poor reversibility issue of sodium plating/stripping in ZSMBs requires attention not only to the substrate sodophilicity, but also to the stability of the interfacial structure and the characteristics of the SEI.