MXene nanofibers confining MnO_<i>x</i> nanoparticles: a flexible anode for high-speed lithium ion storage networks

Abstract

The electron and ion conductivities of anode materials such as MnO_<i>x</i> affect critically the properties of anodes in Li-ion batteries. Herein, a three-dimensional (3D) nanofiber network (MnO_<i>x</i>-MXene/CNFs) for high-speed electron and ion transport with a MnO_<i>x</i> surface anchored and embedded inside is designed <i>via</i> electrospinning manganese ion-modified MXene nanosheets and subsequent carbonization. Ion transport analysis reveals improved Li⁺ transport on the MnO_<i>x</i>-MXene/CNF electrode and first-principles density functional theory (DFT) calculation elucidates the Li⁺ adsorption and storage mechanism. The surface-anchored MnO_<i>x</i> nanoparticles form extremely strong bonds with the nanofibers, and the internally embedded MnO_<i>x</i> 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_<i>x</i>-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_<i>x</i>-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_<i>x</i>-MXene/CNF anode has excellent Li-ion storage properties and great commercial potential.