Bonding VSe 2 ultrafine nanocrystals on graphene toward advanced lithium-sulfur batteries
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Bonding VSe2 ultrafine nanocrystals on graphene toward advanced lithium-sulfur batteries Wenzhi Tian1, Baojuan Xi1, Yu Gu1, Qiang Fu1, Zhenyu Feng1, Jinkui Feng2, and Shenglin Xiong1 () 1
Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, and State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China 2 Key Laboratory for Liquid-Solid Structural Evolution & Processing of Materials (Ministry of Education), School of Materials Science and Engineering, Shandong University, Jinan 250061, China © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 7 April 2020 / Revised: 28 May 2020 / Accepted: 30 May 2020
ABSTRACT Lithium–sulfur batteries have been attracting considerable research attention due to their high energy densities and low costs. However, one of their main challenges is the undesired shuttling of polysulfides, causing rapid capacity degradation. Herein, we report the first example of sulfiphilic VSe2 ultrafine nanocrystals immobilized on nitrogen-doped graphene to modify the battery separator for alleviating the shuttling problem. VSe2 nanocrystals provide numerous active sites for chemisorption of polysulfides as well as benefit the nucleation and growth of Li2S. Furthermore, the kinetic reactions are accelerated which is confirmed by higher exchange current density and higher lithium ion diffusion coefficient. And the first-principles calculations further show that the exposed sulfiphilic planes of VSe2 boost the redox of Li2S. When used as separators within the lithium sulfur batteries, the cell indicates greatly enhanced electrochemical performances with excellent long cycling stability and exceptional rate capability up to 8 C. Moreover, it delivers a higher areal capacity of 4.04 mAh·cm−2 as well as superior cycling stability with sulfur areal loading up to 6.1 mg· cm−2. The present strategy can encourage us in engineering novel multifunctional separators for energy-storage devices.
KEYWORDS sulfiphilic VSe2, lithium–sulfur batteries, nucleation and growth of Li2S, polysulfide electrocatalysis, shuttle effect
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Introduction
Lithium–sulfur batteries (LSBs) have recently been considered as one of the most probable candidates for next-generation rechargeable battery systems due to their high theoretical energy density of 2,600 Wh·kg−1, low cost of sulfur and environmental benignity [1–3]. Despite these visible merits, the commercial application of LSBs has still encountered some great challenges, including low reversible capacities, rapid capacity degradation, and poor Coulombic efficiency (CE), which originate from the shuttle reaction of soluble polysulfide intermediates (Li2Sx, 4 ≤ x ≤ 8) [4–8]. The sluggish redox kinetics and low utilization of sulfur are mainly pertaining to the insulation nature and poor reactivity of sulfur and the discharged products (Li2S). It should be mentioned that the primary problem stems from the dissolution of Li2Sx in organic el
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