Electrochimica Acta 54 (2009) 6713–6717 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Nanosized Si/cellulose fiber/carbon composites as high capacity anodes for lithium-ion batteries: A galvanostatic and dilatometric study J.L. Gómez Cámer a , J. Morales a,∗ , L. Sánchez a , P. Ruch b , S.H. Ng b , R. Kötz b , P. Novák b a Departamento de Química Inorgánica e Ingeniería Química, Campus de Rabanales, Universidad de Córdoba, E-14071 Córdoba, Spain b Paul Scherrer Institut, Electrochemistry Laboratory, CH-5232 Villigen PSI, Switzerland article info Article history: Received 7 April 2009 Received in revised form 24 June 2009 Accepted 27 June 2009 Available online 4 July 2009 Keywords: Silicon lithium alloys Cellulose fiber Conductive carbon black In situ electrochemical dilatometry Lithium-ion batteries abstract Recently, we reported a simple method for obtaining nanosized silicon with promising electrochemical properties as an anode material for lithium-ion batteries; the method involves the formation of a com- posite electrode with cellulose fibers. It is demonstrated that the performance of these electrodes can be enhanced by the addition of conductive carbon black (CCB). This beneficial effect is not only a result of the improvement of electrical conductivity and inter-particle contacts, but also due to a reduction of the expansion and shrinkage undergone by the electrode when Li is inserted into Si or extracted from Li x Si, as revealed by in situ electrochemical dilatometry measurements. The best results were obtained with a CCB of high surface area and porosity. The Si/cellulose fiber/carbon electrodes obtained delivered charge capacities as high as 1800 mAh g -1 and exhibited good capacity retention on cycling. These electrodes also exhibited lower expansion/shrinkage compared to carbon-free electrodes on discharging and charging the cell, respectively. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Attempts to replace graphite as standard anode material for lithium-ion batteries (LIBs) with other materials affording a greater lithium storage capacity have multiplied over the last decade. Recently, a new LIB using a tin-based anode material has been placed on the market [1]. Silicon, which is similarly reactive towards Li as Sn, but lighter, is an attractive alternative for further increasing the charge capacity of this new LIB generation [2]. Each Si atom can reversibly react with 3.75 Li atoms; this is equivalent to a charge capacity (specific charge) of 3579 mAh g -1 [3], compared to only 372 mAh g -1 and 993 mAh g -1 from the reactions of Li with C [4] and Sn [5], respectively. The main shortcoming of silicon is the great volume change it undergoes during lithium alloying/dealloying [6], which causes alloy grains to fracture and electrical contact between them to be lost, ultimately leading to capacity fading on cycling. This shortcoming has been addressed by preparing alternative electrodes of reduced particle size [7,8] or using thin films [9,10], among others. Our group has adopted a different strategy involv- ing the deposition of nanoparticles onto cellulose fibers, a method which had previously been successful with Sn [11], Sb [12], and Si [13]. This latter electrode delivered an average charge capacity of 1400 mAh g -1 , based on Si mass and after 50 cycles. This value exceeded substantially that of an electrode made from pure Si (ca. ∗ Corresponding author. E-mail address: iq1mopaj@uco.es (J. Morales). 400 mAh g -1 after 50 cycles) but it is still far from the theoretical charge capacity cited above (3579 mAh g -1 ). In this work, we improved the performance of this composite electrode with the addition of an appropriate conductive carbon black (CCB) during deposition of nanosized Si particles onto cellu- lose fibers. The electrochemical properties of the composites were characterized by charge/discharge cycling tests, and the electrode expansion and shrinkage effects by means of in situ electrochem- ical dilatometry analysis. The few studies so far reported utilizing this technique [14,15] have proved its suitability for the analysis of the dimensional changes of electrode materials, particularly alloy- based anodes, crucial for the new generation of Li-ion batteries. 2. Experimental Nanosized Si (n-Si) was supplied by Aldrich, cellulose fibers by Arbocel ® , and CCBs by TIMCAL (Super P) and Degussa (Printex XE2), respectively. Scanning electron microscopy (SEM) images were obtained with a JEOL 6400 scanning electron microscope. Specific surface areas and pore volumes were determined with a Micromeritics ASAP 2020 instrument, using N 2 gas as adsorbate at 77 K. Cellulose fibers were added to a suspension of n-Si, or n-Si and carbon, in isopropanol and were then mildly heated (∼363 K) to dryness. Three composites were prepared with the following com- position in weight %: composite A (50 n-Si/50 cellulose fibers); composite B (50 n-Si/40 cellulose fibers/10 Printex XE2); compos- 0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2009.06.085