Super Kinetically Pseudocapacitive MnCo₂S₄ Nanourchins toward High‐Rate and Highly Stable Sodium‐Ion Storage

Abstract Improving surface morphology profiles, i.e., surface area and porosity, by nanostructure/surface engineering is effective in accommodating sodium's ionic and kinetic inadequacies. However, this strategy is limited to only activating the extrinsic pseudocapacitance in terms of improving surface‐based reactions. Herein, it is aimed to improve the sodiation performance by enhancement from both intrinsic and extrinsic pseudocapacitance to maximize sodiation potential of materials. A rarely reported but highly functional spinel MnCo₂S₄ (MCS), is introduced and systematically analyzed using first‐principles investigations, which exhibits energetically favorable charge‐transfer states and strong Na‐ions adsorption kinetics as well as diffusion channels (−3.65 and 0.40 eV respectively). The overall electrochemical redox profiles of the MCS nanostructure is revealed by in situ techniques, which disclose the commencing of partial and then a full conversion‐type sodiation at low discharge potentials (0.52 V vs Na/Na⁺) with fast Na‐ions diffusivity. Assisted by surface engineering technology on the intrinsically pseudocapacitive MCS, the urchin‐like morphology is instrumental in boosting and realizing sodium storage performance, especially the surface capacitive behavior (from 73.4% to 94.1%), prolonged cycling stability (>800 cycles), and high‐rate capability (416 mAh g⁻¹ at 10 A g⁻¹), as well as exhibiting remarkable full cell capability (high rate at 2 A g⁻¹, >200 cycles at 200 mA g⁻¹).