Short communication Carbon coated lithium sulfide particles for lithium battery cathodes Sangsik Jeong, Dominic Bresser, Daniel Buchholz, Martin Winter, Stefano Passerini * University of Muenster, Institute of Physical Chemistry & MEET, Corrensstrasse 28/30 & 46, 48149 Muenster, Germany highlights < Encapsulated lithium sulfide as cathode material for lithium sulfur batteries. < Prevention of polysulfide dissolution by carbon encapsulation of lithium sulfide particles. < High coulombic efficiencies (>99.5%) and stable cycling performance. article info Article history: Received 25 September 2012 Received in revised form 10 January 2013 Accepted 16 January 2013 Available online 6 February 2013 Keywords: Lithium sulfur battery Lithium sulfide Li 2 S Carbon coating PAN abstract In this paper, we investigated the properties of carbon coated lithium sulfide particles prepared following either a dry coating process or a wet coating process, using, respectively, sucrose or polyacrylonitrile (PAN) as carbon source. X-ray diffraction analysis revealed that the crystalline structure of the pristine Li 2 S was basically preserved upon both coating processes. The dry coating process (Li 2 S-C sucrose ) resulted in Li 2 S particles covered only partially by smaller carbon particles, whereas the wet coating method (Li 2 S- C PAN ) gave Li 2 S particles, homogenously decorated with thin carbon flakes. As a result, the cycling per- formance of Li 2 S-C based electrodes was significantly improved, particularly for Li 2 S-C PAN , for which a coulombic efficiency of more than 99.5% was obtained. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Sulfur is considered to be the most promising cathode material for the realization of Next Generation lithium batteries. Its high specific capacity (1672 mAh g 1 ), ten times that of conventional lithium insertion cathodes, promises lithium batteries with a gravimetric energy density far exceeding the 500 Wh kg 1 nee- ded for the realization of electric vehicles and efficient stationary energy storage systems. Unlikely, present sulfur cathodes are affected by severe drawbacks, namely poor coulombic efficiency and active material loss, associated with the solubility of the in- termediate discharge products, as seen in Fig. 1 . Polysulfide dissolution remains still the main hurdle preventing the development of lithium batteries with high gravimetric energy density. Its primary effect consists in reducing the coulombic effi- ciency of the cell and, thus, it can be easily identified comparing the charge and discharge capacities at a given cycle. So far, several at- tempts have been made to prevent the polysulfide dissolution by, for example, using gel-polymer electrolytes and solvent-free polymer electrolytes [1e8], yet unsuccessfully. In fact, these at- tempts have resulted in limited cell capacity retention (about 75% upon 30 cycles) [7]. Other attempts have focused on trapping the sulfur active material in carbon porous structures or networks of carbon fibers and binders [3,6,9e30]. These approaches, however, suffered of the volumetric expansion of the cathode material upon discharge, which leads to its extrusion (or solubilization) out of the caging structure. Very recently [9], Nazar and coll. have reported excellent capacity performance for sulfur electrode supported on carbon nanospheres through a rather complex synthesis. Never- theless, the coulombic efficiency is still an issue, especially con- sidering that the electrodes were tested at relatively high currents, i.e., a short charging time. Combined approaches were also attempted. Novák and coll. [30] showed that the combination of polymer electrolytes and electrode binders allows the realization of Li/S cells with a good cycle life and interesting capacities. However, the coulombic efficiency of these cells was rather low (>87%) thus indicating that the polysulfide dissolution hurdle is still present. The approach reported in here consists in encapsulating lithium sulfide particles (named Li 2 S-C in the following) into a carbona- ceous shell, which can then be used to realize composite electrodes for Li/S cell (Fig. 2). Moreover, the approach of using the end- * Corresponding author. Tel.: þ49 251 8336725; fax: þ49 2518336797. E-mail address: stefano.passerini@uni-muenster.de (S. Passerini). Contents lists available at SciVerse ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2013.01.084 Journal of Power Sources 235 (2013) 220e225