Capillary force induced the sodium metal infusion in the Sn@HCNF scaffold: A mechanical flexible metallic battery

The practical exploitation of the sodium metallic anodes (SMA), especially in the energy-dense battery models, is impeded by the progressive reactivity of the sodium (Na) deposits in the aprotic electrolyte, which leads to the dynamic interfacial properties, Na cation depletion and parasitic substrate pulverization. Through the coaxial electrospinning technique, herein, we exquisitely engineer the spatial arrangement and Na affinity of a mechanical-flexible, lightweight (1.0 mg cm⁻²) SMA scaffold, in which the carbothermal reduced Sn nanocrystallines are homogeneously riveted within the hollow carbon nanofibers (Sn@HCNF). Subsequently, the capillary effect induces the molten Na infusion into the hollow fibers at the preset amount, which enables the Na₁₅Sn₄ alloy formation and simplifies the presodiation procedure. As the pre-infused Na–Sn@HCNF anode (0.5* Na excess) coupled with NaVPO₄F cathode (∼8.6 mg cm⁻²) in a proof-of-concept full cell model (2 mA h), the gravimetric energy density of 311.44 W h kg⁻¹ at the maximized power output of 1245.76 W kg⁻¹ (calculations based on the electroactive materials), as well as the robust cycling (89.6% for 300 cycles) upon various geometric flexing states are simultaneously achieved. This capillary driving strategy provides a scalable, straightforward, site-specific presodiation approach, which encourages the facile prototyping of the mechanical-flexible metallic batteries.