Revealing the\nStructural Architecture of Anions Confining\nMo<sub>2</sub>CT<sub><i>x</i></sub> MXene Layers for Robust\nLi<sup>+</sup> Storage

Controllable cation preintercalation enables enhancing\nthe electrochemical\nactivity and kinetics of MXenes. However, the electrostatic repulsion\nbetween cations and electrolyte ions induces deteriorative electrolyte\nion transport kinetics. Herein, by shifting perceptions from the cation\nto anion strategies, we successfully preintercalate Cl<sup>–</sup>, SO<sub>4</sub><sup>2–</sup>, and PO<sub>4</sub><sup>3–</sup> anions into Mo<sub>2</sub>CT<sub><i>x</i></sub> MXene\nvia the utilization of diverse etching agents. Due to a smaller ionic\nradius and low charge, more Cl<sup>–</sup> ions can be intercalated\ninto Mo<sub>2</sub>CT<sub><i>x</i></sub> MXene and induce\nhigher dislocation density, larger interlayer spacing, and more negative\nZeta potential value. Relying on <i>in situ</i> X-ray diffraction,\nwe monitored the interlayer evolution. The lower lithium-ion concentration\ngradient in the Mo<sub>2</sub>CT<sub><i>x</i></sub> MXene\ndelivers a lower concentration polarization, a fast charge and ion\ntransfer kinetics, and an excellent lifespan, holding 540.49 mAh g<sup>–1</sup> after 400 cycles at 200 mA g<sup>–1</sup>.\nThe effect of anion preintercalation provides new insights into the\nfunction-oriented design of MXene materials.