Accommodating sodium into three-dimensional hosts with a nanoscale sodiophilic layer towards stable pre-stored Na metal anodes

Abstract

Although sodium (Na) metal is a promising anode material for high-energy Na batteries, it is still difficult for it to achieve a long lifespan due to dendrite growth and an unfavorable solid electrolyte interphase (SEI) with sluggish ion transport kinetics. Herein, a facile and mild hydrothermal method is developed to grow vertically aligned ZnO nanosheets on Ni foam, which effectively facilitates uniform thermal infusion and confinement of Na within the three-dimensional (3D) host. In virtue of the large surface area of NF, the local current density can be effectively lowered, which is conductive to uniform Na deposition. More importantly, the products obtained by the reaction between ZnO and Na metal during thermal infusion of Na affect the decomposition of electrolyte, leading to the formation of SEI film with enhanced Na-ion transport property. Electrochemical studies show that the resultant Na-metal/Zn-modified Ni foam composite (Na–Zn-NF) anode can stably cycle for more than 2000 and 550 h at a current density of 1 and 3 mA cm⁻² in symmetric cells, respectively. When assembled into full cells against NaTi₂(PO₄)₃/C (NTP/C) and Na₄Fe₃(PO₄)₂(P₂O₇)/C (NFPP/C) cathodes, the Na–Zn-NF anode also exhibits excellent cycling stability and stable Coulombic efficiencies. This work provides an effective strategy for simultaneously achieving the enhancement of the surface sodiophilicity of 3D hosts and the optimization of an electrode/electrolyte interphase for stable Na metal anodes.