Revealing the Structural Architecture of Anions Confining Mo2CTx MXene Layers for Robust Li+ Storage

Controllable cation preintercalation enables enhancing the electrochemical activity and kinetics of MXenes. However, the electrostatic repulsion between cations and electrolyte ions induces deteriorative electrolyte ion transport kinetics. Herein, by shifting perceptions from the cation to anion strategies, we successfully preintercalate Cl^–, SO₄^2–, and PO₄^3– anions into Mo₂CT_x MXene via the utilization of diverse etching agents. Due to a smaller ionic radius and low charge, more Cl^– ions can be intercalated into Mo₂CT_x MXene and induce higher dislocation density, larger interlayer spacing, and more negative Zeta potential value. Relying on in situ X-ray diffraction, we monitored the interlayer evolution. The lower lithium-ion concentration gradient in the Mo₂CT_x MXene delivers a lower concentration polarization, a fast charge and ion transfer kinetics, and an excellent lifespan, holding 540.49 mAh g^–1 after 400 cycles at 200 mA g^–1. The effect of anion preintercalation provides new insights into the function-oriented design of MXene materials.