A. Chojnacka

Facile synthesis of C/Sn nanocomposite anode material for Li ion batteries

Abstract C/Sn nanocomposites were prepared in simultaneous pyrolysis and carboreduction process (700 and 800°C) of a nanometric tin oxide(IV), obtained by a modified reverse microemulsion method. The proposed method provided formation of tin nanograins encapsulated in conductive carbon layers. The obtained materials with different carbon loadings (13–26 wt-%) were characterised by X-ray diffraction (XRD), low temperature nitrogen adsorption method (N2-BET) and transmission electron microscopy. Galvanostatic discharge/charge tests, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) as well as electrical conductivity studies were used to characterise electrochemical properties of C/Sn nanocomposites. It was found that the electrochemical performance of C/Sn nanocomposites may be affected by carbon matrix morphology.

Pyrolytic carbons derived from water soluble polymers

Conductive pyrolytic carbon materials were obtained in wet impregnation process followed by controlled pyrolysis. Poly-N-vinylformamide (PNVF) as well as mixture of PNVF and pyromellitic acid (PMA) were applied as carbon precursors. Composition of carbon precursors was optimized in terms to obtain best electrical properties of pyrolytic carbons. Mixture of PNVF and PMA as well as pure PNVF were deposited on the model alumina (α-Al2O3) support to form conductive carbon layers (CCL). The optimal composition of the polymer precursors was determined by Raman spectra and electrical conductivity measurements. The carbonization conditions were optimized using complementary thermal analysis methods (EGA(FTIR)–TG/DTG/STDA). It was found that the addition of PMA to polymer precursor PNVF decreases temperature of formation of condensed graphene structures, domains of electrical conductivity, thus, the formation temperature of pyrolytic carbons with desired electrical properties may be decreased.

Multifunctional carbon aerogels derived by sol–gel process of natural polysaccharides of different botanical origin

In this manuscript, we describe the results of our recent studies on carbon aerogels derived from natural starches. A facile method for the fabrication of carbon aerogels is presented. Moreover, the complete analysis of the carbonization process of different starch aerogels (potato, maize, and rice) was performed using thermogravimetric studies combined with a detailed analysis of evolved decomposition products. The prepared carbon aerogels were studied in terms of their morphology and electrical properties to relate the origin of starch precursor with final properties of carbon materials. The obtained results confirmed the differences in carbon aerogels’ morphology, especially in materials’ specific surface areas, depending on the botanical origin of precursors. The electrical conductivity measurements suggest that carbon aerogels with the best electrical properties can be obtained from potato starch.

Effect of electrolyte composition on thermal stability and electrochemical performance of LiMn2O4-ySy cathodes for Li-ion batteries

Electrolytes are indispensable for the proper operation of every battery technology. Hence, in this paper, our major focus concerns identification of the most appropriate electrolyte composition in order to minimise the reactions on the electrode surface as well as enhance the electrochemical performance of Li-ion batteries containing as a cathode LiMn2O4-ySy (LMOS) spinel materials. For this purpose, thermal stability of LiPF6 and LiClO4 salts in a mixture of EC:DEC, TMS:EMC solvents towards LMOS cathode materials was investigated. All the electrolyte solutions were also tested in Li/Li+/LMOS cells. The electrochemical behaviour of electrolyte-cathode material systems was further examined by the electrochemical impedance spectroscopy. As demonstrated, LiMn2O3.99S0.01 (LMOS1) electrode exhibits remarkable thermal and electrochemical stability in LiPF6 solution of alkyl carbonates (EC:DEC). The satisfactory cycling performance is due to the development of highly stable passivating surface film on the LMOS1 cathode in aforementioned electrolyte that protects the active material from unfavourable reactions.

Leak testing of carbon–tin nanocomposites by thermal analysis methods

Electrode materials consisted of tin nanograins encapsulated in different origin carbon buffer matrix (starch or water soluble polymer) were obtained in a simple and inexpensive process. The tin precursor was synthesized using modified reverse nanoemulsion technique (w/o) and then coated by a source of carbon. The composites precursors were pyrolysed, affording formation of C/Sn anode materials. The resulting samples were investigated by powder X-ray diffraction studies in order to verify the structure and calculate crystallites sizes. The morphology of the nanocomposites was characterized by low-temperature nitrogen adsorption method (N2-BET). Thermal analysis measurements (EGA-TG/DTG/DTA and DSC) allowed determining optimal conditions of preparation process and estimating carbon content in the obtained anode materials. Thermogravimetric studies also proved to be highly useful in establishing the leak behaviour of C/Sn nanocomposites. The electrochemical performance of the nanopowders was examined by charge–discharge tests in R2032-type coin cell. The thermal analysis results as well as low-temperature nitrogen adsorption data indicated that the origin of carbon precursor has major impact on morphology and leak behaviour of the obtained carbon buffer matrix. The electrochemical tests showed that better tightness of carbon–tin nanocomposites resulted in higher gravimetric capacity and better cell performance.