Edge-enriched MoS 2 for kinetics-enhanced potassium storage
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ate Key Laboratory of Solidification Processing, Center for Nano Energy Materials, School of Materials Science and Engineering, Shaanxi Joint Laboratory of Graphene (NPU), Northwestern Polytechnical University, Xi’an 710072, China 2 Department of Inorganic Chemistry, Technische Universität Dresden, Bergstrasse 66, 01062 Dresden, Germany © The Author(s) 2020 Received: 3 May 2020 / Revised: 7 June 2020 / Accepted: 8 June 2020
ABSTRACT Potassium-ion batteries (PIBs) hold great promise as alternatives to lithium ion batteries in post-lithium age, while face challenges of slow reaction kinetics induced by the inherent characteristics of large-size K+. We herein show that creating sufficient exposed edges in MoS2 via constructing ordered mesoporous architecture greatly favors for improved kinetics as well as increased reactive sites for K storage. The engineered MoS2 with edge-enriched planes (EE-MoS2) is featured by three-dimensional bicontinuous frameworks with ordered mesopores of ~ 5.0 nm surrounded by thin wall of ~9.0 nm. Importantly, EE-MoS2 permits exposure of enormous edge planes at pore walls, renders its intrinsic layer spacing more accessible for K+ and accelerates conversion kinetics, thus realizing enhanced capacity and high rate capability. Impressively, EE-MoS2 displays a high reversible charge capacity of 506 mAh·g−1 at 0.05 A·g−1, superior cycling capacities of 321 mAh·g−1 at 1.0 A·g−1 after 200 cycles and a capacity of 250 mAh·g−1 at 2.0 A·g−1, outperforming edge-deficient MoS2 with nonporous bulk structure. This work enlightens the nanoarchitecture design with abundant edges for improving electrochemical properties and provides a paradigm for exploring high-performance PIBs.
KEYWORDS molybdenum disulfide, enriched edges, potassium-ion batteries, kinetics
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Introduction
As one of the most promising substitutes for commercial lithium-ion batteries (LIBs), potassium-ion batteries (PIBs) have captured increasing attention owning to natural abundance of potassium in contrast to lithium (17,000 vs. 20 ppm in the earth crust) [1]. Additionally, an intrinsic merit lies in that the redox potential of K+/K (−2.93 V vs. standard hydrogen electrode, Eo) is quite close to that of Li+/Li (−3.04 V vs. Eo), endowing PIBs with a high working voltage and energy density analogue to LIBs [2–5]. Nonetheless, the large radius of K+ (1.38 Å), approximately twice as that of Li+ (0.76 Å), undoubtedly retards “rocking chair” chemistry kinetics and induces acute volume expansion of electrode [6–9], which renders the promising PIBs into a dilemma. Hence, resolving the above-mentioned problems is crucial but challenging for the further development of PIBs. Recent years have witnessed the enormous endeavors devoted to exploring high-performance anodes for PIBs. Given the low cost and easy availability, carbon materials have been investigated, however, their theoretical specific capacity (278 mAh·g–1) remains unsatisfactory according to the formation of one-stage KC8 in graphite structure via the intercalation chemistry [10–12].
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