Electrochemical Properties of Tin Nanoparticles Encapsulated in Different Origin Carbon Buffer Matrix

Tin seems to be a promising anode material due to its lithium uptake at low potential and high theoretical capacity (994 mAh/g for Li_4.4Sn alloy phase). However, the major problem during formation of Li_xSn_y alloys are cyclic changes of elementary cell volume, reaching up to 300%, which lead to loss of electrical contact between active material and current collector as well as physical damage of the cell caused by high strains. Over the last decade most of the studies related to anode materials based on tin were focused on designing composites containing Sn and a stress-accommodating phase [1-4]. Nevertheless, the multi-step processes used to synthesis of such composites are complex and expensive [5].

The goal of the present work was development two types of carbon-tin nanocomposite anode materials and comparison of their electrochemical properties. In both cases the nanocomposites were obtained in a simple and inexpensive process, consisted of tin-based nanograins encapsulated in a flexible carbon buffer matrix derived from plant polysaccharides in the first series and from water soluble polymer in the latter.

The precursor of active material was obtained using a modified reverse microemulsion technique (w/o) and then coated by a source of carbon (potato starch or poly(N-vinylformamide) mixed with pyromellitic acid) [6,7]. The carbon-tin precursors were pyrolyzed, affording formation of tin-based nanograins encapsulated in conductive carbon buffer matrix. Optimal conditions of the thermal treatment were determined by thermal analysis methods (EGA-TGA). The resulting materials with different carbon loading (20-60 wt.%) were investigated by X-ray diffraction (XRD) and by transmission electron microscopy (TEM) as well. Comprehensive electrochemical characterization of obtained nanocomposites including the electrical conductivity (EC), cyclic voltammetry (CV) and impedance spectroscopy (IS) was carried out. Discharge - charge tests were performed in R2032-type coin cells within 0.01–1.5 V potential range.

TEM images indicate that the type of carbon precursor has strong impact on morphology of obtained carbon buffer matrix. The study also showed that columbic efficiency and capacity retention in discharge-charge tests strongly depend on carbon loading and sort of a carbon precursor.

The authors acknowledge a financial support from the National Science Center of Poland under research grant No. 2012/07/N/ST8/03725 and from the European Institute of Innovation and Technology under the KIC InnoEnergy NewMat project.

[1] J. W. Zheng, S. M. L. Nai, M. F. Ng, P. Wu, J. Wei, M. Gupta, J. Phys. Chem. 113 (2009) 14015-14019.
[2] L. Zhao, S. Hu, W. Li, L. Li, X. Hou, Rare Metals 27 (2008) 507-512.
[3] D. Deng, J.Y. Lee, Angew. Chem. Int. Edit. 48 (2009) 1660-1663.
[4] H. Kim, M. G. Kim, T.J. Shin, H. J. Shin, J. Cho, Electrochem. Commun. 10 (2008) 1669-1672.
[5] A. Kamali, D.J. Fray, Rev. Adv. Mater. Sci. 27 (2011) 14–24.
[6] M. Molenda, A. Chojnacka, M. Bakierska, R. Dziembaj, Mater. Technol. 29 (2014) A88-A92.
[7] A. Chojnacka, M. Molenda, M. Bakierska, R. Dziembaj, Procedia Eng. 98 (2014) 2-7.