MXene nanofibers confining MnOx nanoparticles: a flexible anode for high-speed lithium ion storage networks

Abstract

The electron and ion conductivities of anode materials such as MnO_x affect critically the properties of anodes in Li-ion batteries. Herein, a three-dimensional (3D) nanofiber network (MnO_x-MXene/CNFs) for high-speed electron and ion transport with a MnO_x surface anchored and embedded inside is designed via electrospinning manganese ion-modified MXene nanosheets and subsequent carbonization. Ion transport analysis reveals improved Li⁺ transport on the MnO_x-MXene/CNF electrode and first-principles density functional theory (DFT) calculation elucidates the Li⁺ adsorption and storage mechanism. The surface-anchored MnO_x nanoparticles form extremely strong bonds with the nanofibers, and the internally embedded MnO_x nanoparticles, due to the fiber confinement effect, ensure the structural stability during charging and discharging, achieving the so-called dual stabilization strategies for cyclic fluctuation. By electrospinning, self-restacking of MXene flakes can be prevented, thereby giving rise to a larger surface area and more accessible active sites on the flexible anode. Benefiting from the 3D network with excellent conductivity and stability, at high current densities, the MnO_x-MXene/CNF anode exhibits outstanding electrochemical characteristics. Even after 2000 cycles, a reversible capacity of 1098 mA h g⁻¹ can be obtained at 2 A g⁻¹ with only 0.007208% decay rate. The MnO_x-MXene/CNF anode also shows a significant rate performance such as 1268 mA h g⁻¹ at 2 A g⁻¹ and 1137 mA h g⁻¹ at 5 A g⁻¹ corresponding to an area specific capacity of 2.536 mA h cm⁻² at 4 mA cm⁻² and 2.274 mA h cm⁻² at 10 mA cm⁻², respectively. The results indicate that the MnO_x-MXene/CNF anode has excellent Li-ion storage properties and great commercial potential.