Constructing robust and freestanding MXene/Si@C core-shell nanofibers via coaxial electrospinning for high performance Li-ion batteries

Silicon (Si) is a promising anode for Lithum-ion batteries (LIBs) due to its high theoretical capacity (4200 mA h g(-1)). However, low initial Coulombic efficiency (ICE) and utilization efficiency due to volume expansion and poor conductivity hinder the practical application of Si. Herein, a facile coaxial electrospinning method is adopted to fabricate core-shell MXene/Si@C nanofibers, which have a number of unique structure advantages in improving the performance of Si particles. MXene nanosheets as a conductive substrate effectively bridge the Si particles and carbon shell to form the conductive network of the MXene/Si@C nanofibers, which is beneficial for fast charge transfer and facile lithium ion migration. The robust carbon shell and MXene nanosheets offer double accommodation for huge Si volume expansion during charge/discharge, maintaining the structural stability of the electrodes. Moreover, abundant functional group defects associated with the carbon shell and MXene synergistically contribute the additional capacitive capacity. Therefore, the obtained MXene/Si@C nanofibers as a freestanding anode for LIBs present remarkable electrochemical performance, i.e., a high capacity of 1083 mA h g(-1) at 0.1 A g(-1), an excellent rate performance of 301.1 mA h g(-1) at 2 A g(-1), high Si utilization efficiency up to 86% and a high ICE of over 78.4%. A facile coaxial electrospinning technique to construct the core-shell structure of multiple components has the potential to improve the electrochemical performance and facilitate the practical application of Si.