Taguchi optimization of the carbon anode for Li-ion battery from natural precursors Sunil Bhardwaj a, * , Maheshwar Sharon a , T. Ishihara b a Nanotechnology Research Laboratory, Birla College, Kalyan 421 304, India b Department of Applied Chemistry, Faculty of Engineering, Oita University, Dannoharu 700, Oita 870-1192, Japan Received 9 March 2007; accepted 23 May 2007 Available online 6 June 2007 Abstract Soya bean seed (Glysin maze), Baggas fibers (Sacharum officinarum) and Semer Cotton (Bombax ceiba) on pyrolysis give carbon nano- materials, which are tested for their application as anode in lithium ion batteries. Taguchi optimization technique is used to find the best natural precursor, best temperature of the pyrolysis and the effect of pretreatment of acid and alkali to find the best carbon for the elec- trochemical intercalation of lithium. It was found that Baggas is the best precursor over the three precursors and pretreatment with acid and pyrolysis at 700 °C in an inert atmosphere of hydrogen favors the formation of carbon with best lithium intercalation properties. Ó 2007 Elsevier B.V. All rights reserved. PACS: 82.47.Aa; 82.30.Lp; 81.05.Uw; 68.65.k Keywords: Li-ion battery; Pyrolysis; Baggas; Cotton; Soyabean; Carbon nanomaterials; Anode 1. Introduction Graphite is the most commonly used anode for Li-ion secondary battery. Lithium secondary batteries are the only commercially available batteries, which can provide voltage greater than 3 V per cell. Lithium metal anodes, in conjunction with an organic electrolyte, result in a non-uniform formation of a passive film on the anode sur- face [1,2], which causes dendritic growth of lithium metal. This problem is tackled by utilizing the electrochemical intercalation of lithium in carbon, which generates a con- siderable negative potential close to that of lithium, but which is less reactive and easily reversible. Longer charg- ing–discharging cycles are one of the important require- ments for making a commercially viable lithium ion battery. The structural characteristics of carbon are believed to be the major element that controls the perfor- mance of Li-ion batteries. The intercalation of Li-ion with carbon depends upon factors such as the preparative his- tory, and carbon precursor. Recently, attention has been drawn to use disordered carbon materials [3], which may store Li via a mechanism, which is completely different from that associated with graphite. Sharon et al. [4] studied the intercalation of lithium with camphor-based carbon nano-beads and found the cell to be stable for 10–20 days. The reversible Li-ion intercalation capacity was found to be 45–61% of that obtained with graphite [5]. Encouraged by this work it was thought to pyrolyse var- ious parts of the plants like seed, stem and fibers of differ- ent plant to examine which part of the plant and its pyrolysis conditions gives a better lithium intercalation. Because, the structure of carbon fibers obtained by pyroly- sis of plant precursors depend upon the structure of seed and stem. Moreover, no catalyst is needed for the forma- tion of carbon nanomaterial. It is also expected that carbon obtained from the pyrolysis of seeds or stems of plant would produce porous fibers of the type difficult to produce otherwise. Thus it would be interesting to examine the role 1567-1739/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2007.05.003 * Corresponding author. Tel.: +91 251 2230054. E-mail addresses: s_p_bh@rediffmail.com (S. Bhardwaj), sharon@ iitb.ac.in (M. Sharon). www.elsevier.com/locate/cap www.kps.or.kr Current Applied Physics 8 (2008) 71–77