Electrochemical behaviour and morphological characterization of binder-free nano-stratified Si/C anodes for lithium ion batteries

G. PEREYRA; M. OTERO; E.P. M. LEIVA; N. BUDINI; P.D. PEREZ; J. TRINCAVELLI; F. OLIVA.

Workshop; 7th International Workshop on Lithium, Industrial Minerals and Energy; 2020

Celimin, Universidad de Antofagasta, INFIQC, INIFTA, UCA Bolivia

Nano-stratified Si/C anodes for lithium ion batteries were prepared by plasma-enhanced chemical vapor deposition (PECVD) and sputtering deposition. To study the electrochemical properties of the anodes, a good knowledge of the Si and C mass thicknesses is required. Nevertheless, not always is possible to rely on the methods available for this kind of determinations; particularly, when nanometer thicknesses are involved.In the present work, a standardless method recently developed [1] is applied to the determination of the thicknesses required for the anodes developed, based on binder-free Si/C binary composites generated by PECVD and sputtering deposition. The method was developed using characteristic x rays, and although it was specifically designed for nano-stratified samples consisting of a Si film deposited onto a C layer (which in turn is deposited on a Cu substrate), it is also easily applicable to other configurations. Since it is necessary to know the thickness of the surface layer to obtain the thickness of the deepest layer, the calculations involve the application of an iterative strategy based on Monte Carlo simulations.The validation of the method was done by Rutherford backscattering spectroscopy (RBS).The thicknesses of the Si and C layers obtained were used to calculate the specific capacity. Galvanostatic charge-discharge curves up to 100 cycles were analyzed for three anodes with different Si/C ratios, and the experimental results were compared with the theoretical capacity for each binary system.Figure 1 shows the electrochemical performance of one of the Si/C samples studied, as an example. It can be seen that nanostructures designed under controlled Si/C mass ratio conditions retain Si high capacity without the drawback of expansion effects observed in bulk materials and an excellent coulombic efficiency.Figure 1. Experimental Specific Discharge Capacity vs number of cycles obtained using Si 28±4 nm / C 160±20 nm sample as anode material (empty circles). Theoretical Specific Discharge Capacity is shown as a reference (red line). Coulombic efficiency is also included as empty circles, with its values represented on the right vertical axisKeywords: Si/C anodes, nanostructure, lithium ion batteryAcknowledgments: G.P. and M.O. thanks CONICET for the doctoral and postdoctoral fellowships. This work was financially supported by the Secretarı́a de Ciencia y Técnica of the Universidad Nacional de Córdoba (UNC), Argentina. The authors are also grateful to the Laboratorio de Microscopı́a y Análisis por Rayos X (LAMARX-UNC), where the X-ray spectra.References: [1] G. Pereyra, F. Y. Oliva, N. Budini, G. Risso, P. D. Pérez, S. Suárez, J. Trincavelli, Standardless determination of nanometric thicknesses in stratified samples by electron probe microanalysis, Spectrochim. Acta Part B, 171 (2020) 105932. doi:10.1016/j.sab.2020.105932.