Journal of Power Sources 163 (2006) 215–218 Short communication Silicon/graphite composites as an anode material for lithium ion batteries Masaki Yoshio ∗ , Takaaki Tsumura, Nikolay Dimov Department of Applied Chemistry, Saga University, Honjyo 1, Saga City, Saga 840-8502, Japan Received 9 August 2005; received in revised form 18 December 2005; accepted 21 December 2005 Available online 13 February 2006 Abstract Mixed silicon–graphite composites have been prepared by means of mechanical milling process. Their micro-heterogeneous structure is con- sidered responsible for electrode failures. A fingerprint of this process is seen by cycling the carbonaceous component of the composite in an electrolyte containing small amount of propylene–carbonate (PC). Local voltage drops close to 0 V (versus Li metal) resulted in local electrode mechanical deterioration. In the presence of silicon particles such local disorders would lead to a loose interparticle contact (zones called dead spots). Deterioration pattern of the mixed composite electrode may be considered as a set of ‘dead spots’ spreading across the electrode as the cycling proceeds. Hence, a careful optimization is necessary in order to fabricate composite electrode giving minimum local disorders and having satisfactory cycling performance. © 2006 Elsevier B.V. All rights reserved. Keywords: Silicon/graphite composites; Lithium-ion batteries; Alloying electrode; Electrode structure 1. Introduction Recently, there has been a worldwide interest in developing alternative anodes for lithium ion batteries. Fundamental reason for these studies relies on the fact that the potential of the anode versus Li is typically within 0.05–0.5V, which means that the electrochemical reaction at the anode site should not necessar- ily be based on an intercalation type of reaction. Li-metal alloys are the natural alternative to the currently adopted intercalation hosts, such as LiTi 2 O 4 /Li 4 Ti 5 O 12 , and different blends of natural or artificial graphite. An obvious advantage of the binary alloys is that the Li:M mole ratio in the Li x M alloy at the end of charg- ing can be much higher than in the case of intercalation hosts, since the latter generally cannot accommodate and release large amounts of Li + in order to maintain a stable crystal structure over the cycles. Actually, Li-metal alloys have been considered possible anodes even sooner than the currently adopted interca- lation carbonaceous hosts. The first use of lithium alloy anodes was the employment of Wood’s metal (alloy of Bi, Pb, Sn, Cd) in button-type cells developed by Matsushita-Panasonic [1–6]. ∗ Corresponding author. Tel.: +81 952 28 8673; fax: +81 952 28 8591. E-mail address: yoshio@ccs.ce.saga-u.ac.jp (M. Yoshio). The main drawback of these metal electrodes was that reason- able cycling life could be reached only for a very “shallow” cycling mode (<10% depth of discharge). As a result, the spe- cific charge density of the first commercial alloying electrode was an order of magnitude lower than that expected for lithium rich alloys observed at high temperature. Deep cycling of lithium metal-free cells became possible when Sony introduced its car- bon anode-based lithium ion cell in the beginning of 1990s [7,8]. First lithium-ion batteries employed hard carbon with practical capacity in the order of 200 mAh g -1 . Following the invention of new electrolyte additives, practical use of highly crystalline graphite has become possible. Modern graphite anodes have practical capacity in the order of 360 mAh g -1 , which is close to the theoretical stoichiometry with maximal Li uptake (LiC 6 ). Thus, the possibility of improving of carbonaceous anodes is almost exhausted. On the other hand, it is unlikely that signif- icant improvement of the cathode materials can be realized in the near future. Therefore, the only possibility for further sig- nificant improving of the Lithium ion (LION) technology is to develop alternative anodes with a capacity several times higher than that of graphite. Such anodes can be developed by means of light metals from the groups III, IV and V of the periodic table, particularly Sn or Si. The latter two elements offer not only high theoretical capacity in an appropriate potential window, but 0378-7753/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2005.12.078