Surface Charge Engineering for Covalently Assembling Three-Dimensional MXene Network for All-Climate Sodium Ion Batteries

Abstract

MXenes, as excellent candidate anode materials for sodium ion batteries (SIBs), suffer from sluggish ion-diffusion kinetics resulting from the anchoring effect of the negatively charged functional groups on their surface on sodium ions. Herein, we introduce positively charged conductive polyaniline (PANI) to induce self-assembly of Ti₃C₂T_<i>x</i> MXenes into a three-dimensional PANI/Ti₃C₂T_<i>x</i> network. In this PANI/Ti₃C₂T_<i>x</i> network, PANI not only intercalates into Ti₃C₂T_<i>x</i> nanosheets to enlarge the interlayer spacing, but also promotes negative-to-positive transition of the surface charges of the Ti₃C₂T_<i>x</i> nanosheets, significantly improving ion-diffusion kinetics. Electrochemical test results further confirm the superb ion-diffusion kinetics of the PANI/Ti₃C₂T_<i>x</i> network. Meanwhile, a covalent interaction (Ti-N) between PANI and Ti₃C₂T_<i>x</i>, proved by X-ray photoelectron spectra (XPS) and X-ray absorption near-edge structure (XANES) tests, plays a key role in stabilizing this network structure. Therefore, PANI/Ti₃C₂T_<i>x</i> exhibits excellent sodium storage performances with a high specific capacity, superior rate performance and ultralong lifespan at high current density. More importantly, when operated at rigorous temperatures from +50 to -30 °C, PANI/Ti₃C₂T_<i>x</i> also exhibits good electrochemical performances. The present work presents a simple strategy for designing 3D porous MXene-based materials to realize high rate performance and all-climate energy storage device.