A Li-S battery with ultrahigh cycling stability and enhanced rate capability based on novel ZnO yolk-shell sulfur host Ruihan Zhang, Maochun Wu, Xinzhuang Fan, Haoran Jiang, Tianshou Zhao ⇑ Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China article info Article history: Received 28 February 2020 Revised 11 June 2020 Accepted 17 June 2020 Available online 24 June 2020 Keywords: Yolk-shell structure Lithium-sulfur batteries Zinc oxide Shuttle effect In-situ Raman test abstract Currently, lithium-sulfur (Li-S) batteries still suffer from fast capacity decay, poor coulombic efficiency (CE) and short cycling lifespan, which result from the severe shuttle effect issue caused by high solubility and rapid diffusion of lithium polysulfides (LiPSs) in organic electrolytes. Here, yolk-shell zinc oxide (YS- ZnO) spheres are synthesized and for the first time, applied as a host for Li-S batteries to tackle this chal- lenge. The polar ZnO exhibits high chemical anchoring ability toward LiPSs while the unique yolk-shell structure not only provides an additional physical barrier to LiPSs but also enables much more uniform sulfur distribution, thus significantly suppressing LiPSs shuttling effect meanwhile promoting sulfur con- version reactions. As a result, the YS-ZnO enables the Li-S battery to display an initial specific capacity of 1355 mAh g 1 and an outstanding capacity retention capability (~89.44% retention rate) even after 500 cycles with the average CE of ~99.46% at the current of 0.5 C. By contrast, the capacity of conventional-ZnO-nanoparticles based battery severely decays to 472 mAh g 1 after cycling for 500 times. More impressively, the S/YS-ZnO based Li-S battery can maintain a low decay rate of 0.040% every cycle and high average CE of 98.82% over 1000 cycles at 3 C. Ó 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved. 1. Introduction Hitherto, the predominant power sources in the markets of electric vehicles (EVs), mobile electronic products, and static elec- trochemical energy storage systems are still focusing on the lithium-ion batteries (LIBs). Nevertheless, the relatively low energy densities with limited further improvement in the near future have made LIBs far from meeting the ever-increasing requirement for affordable energy sources in modern society [1,2]. On the contrary, the theoretical energy density for the advanced Li-S batteries has attained as high as 2567 Wh kg 1 in the light of the redox reaction between sulfur and Li metal (16Li + S 8 M 8Li 2 S, E° = 2.20 V), which is several times higher than that of commercial LIBs [3,4]. More- over, the Li-S batteries exhibit more benign eco-friendliness and lower energy cost attributed to the nontoxic and abundant feature of sulfur cathode [5,6]. Based on these advantages, the Li-S batter- ies have been gaining intense interest and significant progresses have been achieved. However, the commercial application of this type of battery is still hampered by several challenges, e.g., extre- mely low conductivities of sulfur cathode and the lithium sulfide (Li 2 S), significant volume changes of cathode during charge and discharge processes, as well as the severe ‘‘shuttle effect” as a result of the high solubility of LiPSs [7–9]. During the last decades, a variety of pioneering structures have been proposed to cope with these obstacles. Among them, compos- ing the insulating sulfur with conductive host materials is one of the most attractive approaches, which not only promote the elec- tron transport but also restrain the LiPSs [10,11]. Owing to the high conductivity, light weight and easily structural designs, carbona- ceous materials have been widely utilized for sulfur cathode prepa- ration, such as the hollow carbon spheres [12,13], mesoporous carbon [14], and graphene- or carbon nanotubes (CNTs)- based composites [15,16]. With these carbon-based sulfur hosts, the Li- S batteries exhibit improved electrochemical performance, espe- cially the enhanced specific capacities in the first several cycles. Nevertheless, for the subsequent long-term cycling test, these bat- teries still suffer from a low CE and thus severe capacity decay, which is mainly ascribed to the fact that the nonpolar carbon fails to provide strong enough physical confinement to diminish the dissolution of the inherently high-polar and ionic polysulfides over long-time operation [17,18]. In contrast, many polar materials, especially metal oxides, are inherently polar-group-materials, which could form strong polar-polar chemical interactions with these long-chain LiPSs without further modifications [19–25]. On https://doi.org/10.1016/j.jechem.2020.06.039 2095-4956/Ó 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved. ⇑ Corresponding author. E-mail address: metzhao@ust.hk (T. Zhao). Journal of Energy Chemistry 55 (2021) 136–144 Contents lists available at ScienceDirect Journal of Energy Chemistry journal homepage: www.elsevier.com/locate/jechem