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 MnOx affect critically the properties of anodes in Li-ion batteries. Herein, a three-dimensional (3D) nanofiber network (MnOx-MXene/CNFs) for high-speed electron and ion transport with a MnOx 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 MnOx-MXene/CNF electrode and first-principles density functional theory (DFT) calculation elucidates the Li+ adsorption and storage mechanism. The surface-anchored MnOx nanoparticles form extremely strong bonds with the nanofibers, and the internally embedded MnOx 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 MnOx-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 MnOx-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 MnOx-MXene/CNF anode has excellent Li-ion storage properties and great commercial potential.