3D N-Ti3C2Tx/Co/N-CNT composites as a sodiophilic framework for dendrite-free sodium metal anodes

Abstract

Benefiting from the high theoretical capacity, abundant resource and low working potential, Na metal has been considered as a promising anode for sodium-based batteries. However, the growth of Na dendrites and severe volume variation upon cycling greatly hinder the development of Na metal anodes. Herein, N-doped Ti₃C₂T_x/N-doped carbon nanotube-based composites, where N-doped carbon nanotubes are distributed on N-doped Ti₃C₂T_x MXenes, are fabricated via Lewis acidic salt etching and subsequent annealing treatment. As a proof of concept, owing to superior sodiophilicity derived from –O termination and ample N species, outstanding Na⁺ diffusion kinetics and electronic conductivity as well as large specific area, N-doped Ti₃C₂T_x/Co/N-doped carbon nanotubes (TCC) can induce Na uniform nucleation and deposition, mitigate volume expansion and accelerate the plating/stripping kinetics when used as three-dimensional frameworks for the Na metal anode, thus achieving dendrite-free growth and considerably enhanced electrochemical performance. Specifically, the TCC electrode exhibits a low nucleation overpotential of 6 mV at 1 mA cm⁻² and a high average coulombic efficiency of 99.9% at 2 mA cm⁻² in asymmetric cells, and stably cycles for 1300 h at 1 mA cm⁻² and 1 mA h cm⁻² in symmetric cells. Moreover, excellent cycling performance can be achieved by the full cells with a capacity retention of 85.5% after 1200 cycles at 4C.