Carbon-rich SiCN ceramics as high capacity/high stability anode material for lithium-ion batteries Lukas Mirko Reinold * , Magdalena Graczyk-Zajac, Yan Gao, Gabriela Mera, Ralf Riedel Technische Universität Darmstadt, Fachbereich Material- und Geowissenschaften, Fachgebiet Disperse Feststoffe, Petersenstraße 32, 64287 Darmstadt, Germany highlights < SiCN ceramics were investigated in terms of Li-ion storage capacity. < Influence of microstructure on electrochemical properties of SiCN was studied. < Oxygen to nitrogen ratio was found to be irrelevant for capacity of SiCN. < SiCN is potential candidate to replace graphite anodes in lithium-ion batteries. < No linear relationship between free carbon content and capacity was found for SiCN. article info Article history: Received 1 November 2012 Received in revised form 14 February 2013 Accepted 18 February 2013 Available online 26 February 2013 Keywords: Lithium-ion battery Polymer-derived ceramic Silicon carbonitride Anode Polysilazane Polysilylcarbodiimide abstract Two classes of preceramic polymers, namely polysilazane and polysilylcarbodiimide, with branched and linear molecular structure were pyrolyzed at 1100  C under argon atmosphere. The resulting nano- structured polymer-derived SiCN ceramics were characterized by means of elemental analysis, X-ray diffraction, scanning electron microscopy and Raman spectroscopy. All investigated ceramics are amorphous and contain a disordered free carbon phase of 2e2.5 nm in size. Electrochemical characterization reveals that the polysilazane-derived electrodes demonstrate higher capacity and sta- bility during subsequent lithium insertion/extraction with different currents than those of the polysilylcarbodiimide-based electrodes. The highest lithium extraction capacity of 724 mA h g 1 is recovered for the sample derived from branched polysilazane whereas the best polysilylcarbodiimide- derived sample recovers 612 mA h g 1 . Moreover, the polysilazane-derived samples deliver a higher fraction of capacity recovered below 1.5 V. The electrochemical performance is found to be dependent on the molecular structure (silazane vs. silylcarbodiimide) of the preceramic polymer, while there is no effect associated with the amount of branching (silsesquiazane vs. silazane and silsesquicarbodiimide vs. silylcarbodiimide). The influence of “micropore activity” and oxygen content on the electrochemical performance of polymer-derived silicon carbonitrides is addressed. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Polymer-derived ceramics (PDCs) have recently attracted an increasing attention in view of a possible application as anode materials in lithium-ion batteries. This class of materials can exhibit capacities exceeding that of graphite and furthermore show stable cycling behavior even at elevated charge/discharge rates. There is a clash of opinions with respect to the storage sites of lithium in PDCs. Ahn et al. claim that the mixed bond configuration (tetrahedrally coordinated silicon from SiC 4 via SiC 3 O, SiC 2 O 2 and SiCO 3 to SiO 4 ) of SiOC ceramics acts as major lithiation site [1], while Fukui et al. found the free carbon phase within these mate- rials to provide the major hosting site for Li ions [2]. So far, comparing pure PDCs, most of the publications related to the electrochemical performance of PDCs have been focused on SiOC ceramics [1e5]. Even though Dahn et al. had already patented the use of silazane-derived SiCN ceramics in 1997 showing reversible discharge capacities up to 560 mA h g 1 [6], little research has been done on the application of these materials in lithium-ion batteries since that time. Pure PDC-based SiCN materials derived from pol- ysilylethylenediamine have been investigated by Su et al. [7] and Feng [8]. The work of Su et al. showed a first discharge cycle ca- pacity of 456 mA h g 1 but the material suffered from strong fading with cycling. This problem of capacity fading was solved by Feng who achieved capacities higher than 300 mA h g 1 after 30 cycles for a current rate of 160 mA g 1 after an additional heat treatment * Corresponding author. Tel.: þ49 (0)6151 16 6343; fax: þ49 (0)6151 16 6346. E-mail address: reinold@materials.tu-darmstadt.de (L.M. Reinold). 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.2013.02.046 Journal of Power Sources 236 (2013) 224e229