High performance Si/MgO/graphite composite as the anode for lithium-ion batteries Wenchao Zhou, Shailesh Upreti, M. Stanley Whittingham ⁎ Chemistry and Materials, State University of New York, Binghamton, New York 13902-6000, USA abstract article info Article history: Received 24 June 2011 Received in revised form 12 July 2011 Accepted 12 July 2011 Available online 21 July 2011 Keywords: Lithium battery Anode The Si/MgO/graphite composite was synthesized by high energy ball-milling and evaluated as a durable anode for lithium-ion batteries. EDX mapping indicated that Si was dispersed homogeneously in the MgO matrix. The composite delivered an initial capacity of ~ 700 mAh/g and maintained a capacity of 630 mAh/g after 74 cycles at 0.5 mA/cm 2 ; even at 8 mA/cm 2 it delivered more than 85% of its capacity. Its volumetric capacity is double that of carbon. The coulombic efficiency climbed from 77% in the first cycle to above 99.5% after 20 cycles, and retained that value. © 2011 Elsevier B.V. All rights reserved. 1. Introduction A major limitation to the advancement of lithium batteries is the poor volumetric capacity of the carbon anode. Si based anode attracts great research attention as a candidate because of its high theoretical capacity (~4200 vs. 372 mAh/g for graphite) [1]. However, the huge volume expansion/contraction during lithiation isolates the Si particles inside the bulk material and therefore deteriorates the cycling performance [2,3]. One strategy to improve the cycleability of Si anode is embedding the active Si particles in a conductive matrix [3]. In Si/C composites [4–9] the carbon matrix buffers the volume expansion, maintains good electronic contact with Si, and much improves the cycleability but not sufficiently. Another approach is to use Si/SiO y /C nanocomposites [10–15] made for example by ball-milling SiO with graphite followed by annealing at high temperature with a carbon precursor [10]. Si nanoclusters were dispersed in a silicon oxide/carbon matrix, and showed a cycle life up to 200 cycles. Disproportionating SiO at a high temperature into a carbon matrix [12,15] or ball-milling SiO and graphite [11,13] leads to SiO/graphite durable anodes with stable cycling at moderately low current rate. The SiO is composed of nano- sized Si surrounded with silicon oxides of various valence states [12]. Others have formed Si from SiO by Al or lithium metal reduction [14,16]. These results suggest that dispersing Si in an oxide/carbon matrix is an effective way to compensate for the volume change of Si. In this report we synthesized a Si/MgO/graphite composite anode where Si was fixed in an MgO matrix by simple ball-milling. It shows superior capacity retention and rate capability. 2. Experimental The Si/MgO/graphite (SMOG) composite was synthesized by a two- step high energy ball-milling (HEBM) process with a Spex 8000M machine. A 1:1 molar ratio of SiO (optical grade, Alfa Aesar) and Mg (99%, Aldrich) powder was mixed in a zirconia can and ball-milled with four zirconia balls (Φ = 0.8 cm) for 4 h. Then graphite (b 20 μm, synthetic, Aldrich), of weight equal to the total of SiO plus Mg, was added and it was further ball-milled for 0.5 h. The structure of the samples was characterized by Scintag XDS2000 diffractometer. Surface morphology and elemental mapping were determined by scanning electron microscopy (SEM, ZeissSupra-55). Electrochemistry Communications 13 (2011) 1102–1104 ⁎ Corresponding author. Tel./fax: + 1 607 777 4623. E-mail address: stanwhit@gmail.com (M.S. Whittingham). Fig. 1. XRD patterns of Si/MgO/graphite (SMOG), Si/MgO (SMO) and starting materials. 1388-2481/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2011.07.006 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom