Amorphous carbon-coated prickle-like silicon of micro and nano hybrid anode materials for lithium-ion batteries Jung Sub Kim a,b , Martin Halim a,c , Dongjin Byun b , Joong Kee Lee a,c, ⁎ a Center for Energy Convergence, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea b Department of Material Science & Engineering, Korea University, Seoul 136-713, Republic of Korea c Department of Energy and Environmental Engineering, University of Science and Technology, Gwahangno, Yuseong-gu, Daejeon, 305-333, Republic of Korea abstract article info Article history: Received 18 November 2013 Received in revised form 4 March 2014 Accepted 11 March 2014 Available online 28 March 2014 Keywords: Prickle-like silicon Carbon coating Polypropylene Thermal chemical vapor deposition Carbon coated prickle-like Si particles (PS@C) are prepared by metal-assisted chemical etching and subsequent coating with an amorphous carbon film carried out by thermal chemical vapor deposition (CVD). The electro- chemical characteristics of PS@C employed as anode material for lithium-ion batteries are investigated in order to find a relationship between interfacial properties and electrochemical performance. The unique morphology of prickle-like Si (PS) having empty space can accommodate volume expansion during the lithiation and delithiation. Additionally, an amorphous carbon coating layer with a thickness of 10–15 nm deposited onto the PS prepared by thermal CVD is investigated as an effective way to enhance the cycle stability and rate capability of the PS electrode due to improved interfacial characteristics. The micro and nano hybrid structure of the PS ma- terial combined with the 12 wt.% amorphous carbon layer plays an important role in enhancing the electrochem- ical performance. © 2014 Elsevier B.V. All rights reserved. 1. Introduction As a prospective anode material for lithium-ion batteries, Si has been considered as an alternative to carbon-based anodes for next generation lithium-ion batteries because of its natural abundance, availability, environmental friendliness, and most importantly its low discharge po- tential and high theoretical capacity (4200 mA h g -1 in Li 4.4 Si) [1]. How- ever, the practical application of Si anodes has so far been mainly hindered by its low electrical conductivity, low lithium diffusion rate and enormous volume change (300–400%) occurring during the dis- charge (lithiation) and charge (delithiation) process [2]. The volume change causes bulk Si to be pulverized and lose electrical contact with the conductive additive or current collector, and can also lead to the in- stability of the solid electrolyte interphase (SEI) [3]. The latter issue en- courages continuous consumption of Li-ions for reformation of the SEI layer caused by the breakage of the silicon surface with the progress of the cycle, which leads to an increase in irreversible capacity. In order to improve the cycling stability of Si anodes, great efforts have been made to mitigate the pulverization of Si and improve the stability of the SEI layer. These efforts include the development of Si materials composed of nanostructures, porous structures, or nano-composites, the addition of coating layers, and the application of electrolyte addi- tives and novel binders [4–8]. These studies investigate the fact that morphology, volume change, conductivity and surface characteristics of the Si-based electrode materials play a key role in producing high performance active material as anode in lithium-ion batteries. In partic- ular, carbon coating the surface of the active material is very useful due to its nature of forming a stable SEI, structural integrity, and high electric conductivity [9,10]. Accordingly, the well-defined uniformity of carbon layer is of high importance for the electrode performance. Since the nanostructured materials have a small size and large sur- face area, they are expected to inherently provide short diffusion length for lithium-ions, large interfacial area between the electrodes and the electrolyte, and large alleviation of lattice stress during the operation in lithium-ion batteries. Studies of Si as an anode material are leaning toward almost the whole nanostructure area [11–13]. The nano- structuring of electrodes has been demonstrated to result in lithium- ion batteries with superior electrochemical performance, i.e. higher storage capacity, higher rate capability, and excellent cycling perfor- mance. In contrast, the high surface area of nanostructured materials may result in undesirable side reactions with the electrolyte under certain conditions, leading to a significant fading of Li storage capacity and, therefore, poor cycling performance. To avoid these undesired problems, various surface modification or morphologies have been inves- tigated such as hollow, core–shell, nanotube, and nest structures [14–17]. On the other hand, when micro-sized Si (10 μm) is fabricated as an anode to be made into a cell, it has a discharging capacity of only Solid State Ionics 260 (2014) 36–42 ⁎ Corresponding author. E-mail address: leejk@kist.re.kr (J.K. Lee). http://dx.doi.org/10.1016/j.ssi.2014.03.013 0167-2738/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi