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

• Published in: Advanced functional materials Vol. 30; no. 13
• Main Authors: Lim, Yew Von, Huang, Shaozhuan, Wu, Qingyun, Kong, Dezhi, Wang, Ye, Zhu, Yanfang, Wang, Yanxia, Wang, Yun‐Xiao, Liu, Hua‐Kun, Dou, Shi‐Xue, Ang, Lay Kee, Yang, Hui Ying
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.03.2020
• Subjects: ab initio studies; bimetallic metal sulfides; Charge transfer; electrode materials; Ion storage; Materials science; Morphology; Nanostructure; operando techniques; Porosity; pseudocapacitance; Reaction kinetics; Sodium; sodium‐ion batteries
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201909702

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). Binary sulfide materials possess excellent facilitating qualities that are able to alleviate sodium's ionic‐diffusive disadvantages. Capitalized by the strong inherent pseudocapacitive sodiation of the rarely discussed MnCo2S4, a novel hydrolysis‐based surface enhancement is developed to elicit its extrinsic pseudocapacitance, which exhibits remarkable rate and cycling performance.