Energetic and Phonon Dispersion of Lithium Silicates Formed in Operando Reduction of SiO2 with Li in Lithium-ion Battery. A Theoretical and Experimental Study

G. LENER; C.B. ROBLEDOA, M. OTEROA, G. LUQUEA, O. CÁMARAA, D. BARRACOB, M.I. ROJASA, E.P.M. LEIVAA; D. BARRACO; E. LEIVA

Buenos Aires

Simposio; . 20th Topical Meeting of the International Society of Electrochemistry.; 2017

International Society of Electrochemistry

Energetic and phonon dispersion of lithium silicates formed in- operando reduction of SiO2 with Li in lithium ion battery. A theoretical and experimental study.G. Lener,1 M. Otero,1,2 D. Barraco,1 E. P. M. Leiva.2 1 IFEG-Conicet. Facultad de Matemática Astronomía y Física. Universidad Nacional de Córdoba2 INFIQC-Conicet. Departamento de Química Teórica y Computacional. Facultad de Ciencias Químicas. Universidad Nacional de Córdoba.Haya de la Torre s/n. Ciudad Universitaria. Córdoba. Argentina.germanlener@gmail.com.Most of materials used for lithium-ion battery are based in anodes with silicon as active material due that the theoretical capacity of silicon is about of 3800 mAhg-1 which is significantly grater than graphite (420 mAhg-1) [1]. As well know the silicon expand the volume 400 % in the formation of LixSiy alloy and it change of volume produce the pulverization of the electrode. A possible solution is coated silicon with carbon so as avoid the expansion of silicon [2]. However, the reduction of silica to silicon is a process highly activated and expensive. An alternative it could be use SiO2 coated with carbon due that the silicon is formed in-operando, and the theoretical capacity can be calculated trough the following reaction (considering Li4SiO4 and Li2O as majoritary products) [2]:8Li+ + 8e- + 3 SiO2 -----> 2Li2O + Li4SiO4 + 2Si (1) Theoretical Capacity= 950 mAhg-1 xSi + yLi+ + ye- --------> LiySix The high capacity involved in the reaction 1 can be concern a good alternative to get stable and high power anodes with low coast and facile preparation. Moreover silica is one of most abundant component in the Earth´s crust and constitutes almost clays. Even though in the recent years was increase the studies of SiO2 (nanoparticles, meso and micrporous, among others) applied to lithium ion battery in the bibliography practically there is no information about the free energies of formations of different lithium silicates. We use the free energy calculation to obtain the complete thermochemical energy and on the other hand to study how the vibrational entropy of vibration of Li+ in different products of reactions affect at the free energy. In this work we used Quantum Espresso software with phonon implementation to get the internal and vibrational energy to obtain the free Helmholtz energy of formation of several silicates from the lithiation of silica. On the other hand, this results are compared with charge/discharge and rate capability performance of mesoporous coated SiO2/C. We found a high exothermic energies in the irreversible reactions and theses energies are strongly dependent of the type of lithium silicate formed. On the other hand, the vibrational analysis allowed the study of the Li+ entropy in the lattice of different lithium silicates and how affect in the energetic of the reactions.References1- Yoshio, M.; Wang, H.; Fukuda, K.; Umeno, T.; Dimov, N.; Ogumi, Z. J. Electrochem. Soc. (2002) 149, A1598.2- Li, H. H.; Wu, X. L.; Sun, H. Z.; Wang, K.; Fan, C. Y.; Zhang, L. L.; Yang, F. M.; Zhang, J. P. J. Phys. Chem. C (2015) 119, 3495?3501.