An elastic carbon layer on echeveria-inspired SnO 2 anode for long-cycle and high-rate lithium ion batteries A-Young Kim a,b , Jung Sub Kim a,b , Chairul Hudaya a,c,f , Dongdong Xiao d , Dongjin Byun b , Lin Gu d,⇑ , Xiao Wei e,⇑ , Yuan Yao d , Richeng Yu d , Joong Kee Lee a,c,⇑ a Center for Energy Convergence Research, Green City Research Institute, Korea Institute of Science and Technology (KIST), Hwarangno 14 gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea b Department of Material Science and Engineering, Korea University, Anam dong 5 ga, Seongbuk-gu, Seoul 136-701, Republic of Korea c Department of Energy and Environmental Engineering, Korea University of Science and Technology, Gajungro 176, Yuseong-gu, Daejeon 305-350, Republic of Korea d Beijing National Laboratory for Condensed Matter Physics Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China e Department of Material Science and Engineering, Zhejiang University, Hangzhou 310027, China f Department of Electrical Engineering, University of Indonesia, Kampus Baru UI, Depok 16424, Indonesia article info Article history: Received 21 March 2015 Received in revised form 5 June 2015 Accepted 10 July 2015 Available online 10 July 2015 abstract The commercialization of Sn-based anodes for lithium ion batteries is still hindered due to the inherent volume change leading to a rapid capacity fading during the electrochemical cycle. Inspired by echeveria, a plant that stores sufficient water in its hierarchical leaves to survive in a drought, we report a break- through by designing the hierarchical and nanoporous SnO 2 electrode encapsulated with ultrathin carbon layer (2 nm). As evidently captured by in situ transmission electron microscopy, the conformal carbon coating on the surface of anode may provide an elastic cover that suppresses the cracks due to severe vol- ume change, and increases both electrical and ionic conductivity, allowing the cells to exhibit excellent lithium storage performance with more than 800 cycles even with relatively high-rate of current densities. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The development of high-capacity anode materials for lithium ion batteries (LIBs) is a key step toward achieving large-scale energy storage applications for portable electronic devices, electri- cal vehicles, and hybrid electrical vehicles [1]. Since its first discov- ery, the current commercial LIBs have been using graphite as anode material. Although this carbon-based anode is cheap, abundant and reliable, however it provides a limited theoretical capacity of 372 mA h g 1 , hence hampering the establishment of high-energy density LIBs to meet huge technological demands in the near future [2]. To replace the incumbent anode, intensive research has been devoted on the alloy-based materials such as silicon, ger- manium, tin, and tin oxide (SnO 2 ) [3]. Among these candidates, SnO 2 is a promising anode material attributing to its low cost, non- toxicity, low operating potential (0.25 V vs. Li/Li + ), high theoretical capacity (782 and 1493 mA h g 1 for alloying/de-alloying and both alloying/de-alloying and conversion reaction, respectively) [4], and easy synthesis in regard to nanostructures [5]. It was widely studied that employing the pristine SnO 2 anode for LIBs may face a significant barrier because of a severe volume change during the electrochemical cycle, causing pulverization and cracks and eventually the loss of electrical conduction paths. In the meantime, the new-fresh cracks that are exposed to the electrolyte may form a continuous solid electrolyte interphase (SEI)-filming process resulting in a thickened SEI layer on the surface of SnO 2 anode. Consequently, the cell cannot avoid a rapid capacity fading [6]. To overcome these problems, researchers have attempted sev- eral approaches. One strategy is to develop electrode materials based on nanostructures that minimize strain during volume expansion and contraction [7]. Low-dimensional nanostructures such as nanorods, nanowires, nanotubes, and nanosheets have been proposed to sustain large lithium insertion/extraction strain of SnO 2 anode [8–10]. Another effort is to integrate a flexible and stable cover layer like amorphous and mesoporous carbon, graphene, or carbon nanotubes into the electrode material as a physical matrix to effectively mitigate the pulverization [11,12]. It is well known that the carbon content is crucial to the electro- chemical performance. Therefore, appropriate thickness of carbon film with high elasticity is of important to accommodate the strain http://dx.doi.org/10.1016/j.carbon.2015.07.041 0008-6223/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding authors at: Center for Energy Convergence Research, Green City Research Institute, Korea Institute of Science and Technology (KIST), Hwarangno 14 gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea (J.K. Lee). E-mail addresses: l.gu@iphy.ac.cn (L. Gu), mseweixiao@zju.edu.cn (X. Wei), leejk@kist.re.kr (J.K. Lee). CARBON 94 (2015) 539–547 Contents lists available at ScienceDirect CARBON journal homepage: www.elsevier.com/locate/carbon