Electrochimica Acta 56 (2011) 4717–4723 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Amorphous silicon–carbon based nano-scale thin ﬁlm anode materials for lithium ion batteries Moni Kanchan Datta a , Jeffrey Maranchi b , Sung Jae Chung c , Rigved Epur c , Karan Kadakia d , Prashanth Jampani d , Prashant N. Kumta a,c,d,e,f,∗ a Bioengineering, Swanson School of Engineering, University of Pittsburgh, PA 15261, United States b Applied Physics Laboratory, Johns Hopkins University, Baltimore, MD 20723, United States c Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, PA 15261, United States d Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, PA 15261, United States e School of Dental Medicine, University of Pittsburgh, PA 15261, United States f Director, Center for Complex Engineered Multifunctional Materials, University of Pittsburgh, PA 15261, United States article info Article history: Received 5 November 2010 Received in revised form 29 January 2011 Accepted 29 January 2011 Available online 21 February 2011 Keywords: Thin nanolayer ﬁlms Amorphous Si/C Magnetron sputtering Li-ion batteries Anode abstract The buffering effect of carbon on the structural stability of amorphous silicon ﬁlms, used as an anode for lithium ion rechargeable batteries, has been studied during long term discharge/charge cycles. To this extent, the electrochemical performance of a prototype material consisting of amorphous Si thin ﬁlm (∼250 nm) deposited by radio frequency magnetron sputtering on amorphous carbon (∼50 nm) thin ﬁlms, denoted as a-C/Si, has been investigated. In comparison to pure amorphous Si thin ﬁlm (a-Si) which shows a rapid fade in capacity after 30 cycles, the a-C/Si exhibits excellent capacity retention displaying ∼0.03% fade in capacity up to 50 cycles and ∼0.2% after 50 cycles when cycled at a rate of 100 A/cm 2 (∼C/2) suggesting that the presence of thin amorphous C layer deposited between the Cu substrate and a-Si acts as a buffer layer facilitating the release of the volume induced stresses exhibited by pure a-Si during the charge/discharge cycles. This structural integrity combined with microstructural stability of the a-C/Si thin ﬁlm during the alloying/dealloying process with lithium has been conﬁrmed by scanning electron microscopy (SEM) analysis. The buffering capacity of the thin amorphous carbon layer lends credence to its use as the likely compliant matrix to curtail the volume expansion related cracking of silicon validating its choice as the matrix for bulk and thin ﬁlm battery systems. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Generation of electricity from renewable energy sources, such as solar or wind, without producing carbon dioxide, an undesir- able green house pollutant, offers enormous potential for meeting future energy demands [1–3]. However, the electricity gener- ated from these intermittent renewable sources requires efﬁcient electrical energy storage (EES) devices for effective delivery of uninterrupted electricity (power storage back up) and load lev- eling as well as grid energy storage [1–4]. In addition, there is a great need for improved EES devices to transition from today’s hybrid electric vehicular state enabling the realization of plug-in hybrids or the much desired all-electric vehicles (EVs) [1–4]. Chem- ical energy storage technologies based on rechargeable lithium ∗ Corresponding author at: Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, PA 15261, United States. Tel.: +1 412/648 0223; fax: +1 412 624 3699. E-mail address: pkumta@pitt.edu (P.N. Kumta). ion batteries are among the leading EES technology, and in recent years have emerged as the ﬂagship battery technologies offering the much desired hope for both electric vehicles as well as stand- alone stationary power systems [1–6]. Portable EES using lithium ion rechargeable batteries have become thus the primary energy storage engine feeding the wireless revolution for cellular tele- phones and laptop computers, with hybrid electric vehicles (HEV), and electric vehicle (EV) technology following in close pursuit. However, the performance afforded by current lithium ion battery technologies is very much inferior and is unable to meet the colossal energy storage requirements allowing the efﬁcient use of electrical energy in transportation, commercial, and residential applications. For example, most EES devices based on lithium ion batteries need substantially higher energy and power densities, combined with faster charge/recharge rates if electric/plug-in hybrid and elec- tric vehicles are to be deployed as the universal replacements to gasoline-powered vehicles. Development of novel electrode materials and electrolytes is thus essential if lithium ion batteries are to deliver higher energy and power densities. Identiﬁcation of new systems and improve- 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.01.124