Modulating the confined Na deposition via a carbon hollow tube decorated with in-situ formed sodiophilic NaZn13 alloys

Abstract

Owing to its high theoretical specific capacity, low redox potential, and abundant reserves, the sodium metal is considered as the most potential anode for next-generation sodium metal batteries (SMBs). However, the unavoidable growth of sodium dendrites and the highly reactive nature of sodium severely hinders the large-scale applications of SMBs. Herein, a nitrogen-doped carbon hollow tube (CHT) with ultrafine zinc oxides embedded in the tube wall was constructed to be used as a host for sodium metal anode. On one hand, the ultra-fine ZnO can be in-situ converted to NaZn₁₃ alloys during cycling, which serve as excellent sodiophilic sites significantly reducing the nucleation barrier of Na and thus promoting the uniform Na deposition. On the other hand, the hollow tubular structure effectively alleviates the volume change of Na and offers confined space for sodium storage. Consequently, the as-designed CHT-8 electrode exhibits a low nucleation overpotential of only 20 mV even at 5 mA cm⁻². Additionally, the Na@CHT-8||Na@CHT-8 symmetric cell can stably cycle for over 2000 h at 5 mA cm⁻² without dendrites growth, as confirmed by the in-situ optical microscopy observations. Moreover, the full cell assembled with the Na@CHT-8 anode and Na₃V₂(PO₄)₃ cathode exhibits excellent rate capability up to 20 C and maintains a reversible capacity of 72 mAh g⁻¹ even after more than 2000 cycles at 5 C with a capacity retention rate of 82.6 %. Therefore, this work provides a simple and effective strategy to modulate the confined and uniform Na deposition for high-performance SMBs.