Study of Electrochemical Properties in the Lithiation of an Amorphous Silicon Structure Using a DFTB Potential

F. FERNANDEZ; M. OTERO; S.A. PAZ; B. OVIEDO; D. BARRACO; E. LEIVA

Mar del Plata

Congreso; 34 th Topical Meeting of ISE; 2023

To make the transition to cleaner energy sources, energy storage and transportation systems play a key role due to the intermittency of these forms of energy generation. Among these systems, lithium-ion batteries (LIB) are of significant economic and technological interest for Argentina. Due to its abundance, low cost, low discharge potential, and high theoretical lithium capacity of 3579 mAhg-1 silicon was proposed to replace current LIB anodes. Along with these advantages, the material exhibits a large volumetric expansion with lithiation, on the order of 300%, and structural changes that cause a rapid drop in capacity with cycling.In this work, two parameterizations for the Li-Si system, based on the Materials Project structures of pure elements and their crystalline alloys, are developed from Density Functional based Tight Binding (DFTB), which is a fast and efficient quantum mechanical simulation method. The first one (A) is constructed by fitting the band structure of pure Li and Si crystals. The second (B) is constructed by fitting the band structure of Li7Si3, which is the crystalline structure with the lowest formation energy,. In both cases, the structures that were not used for the band structure are used to find the pairwise repulsion term.Figure 1. Radial distribution function (RDF) of amorphous silicon for the different parameterizations of the developed DFTB potentials. The results are compared with experimental values [1], with one of the parameterizations showing a high agreement, and with the ReaxFF [2]. The vertical dashed gray lines show where the peaks of crystalline silicon would be at 0 K.Figure 1 shows the results obtained for the pairwise radial distribution function (RDF) for Si-Si, which gives us information on whether the structure is crystalline or amorphous, after simulated annealing performed in the NVT ensemble. We see that one of the parameterizations (B) shows high agreement with experimental values found in the literature for amorphous Si [1], while the other parameterization (A) reaches a structure that still evidences some crystallization. On the other hand, a previous potential for the LiSi system (ReaxFF) [2] presents agreement with the first peak but shows an intermediate artifact between this peak and the second one.Together with this RDF, different results of computational simulations of molecular dynamics with this new potential will be presented, such as the potential curve versus Li/Li+, the volumetric change of the structures, the diffusion coefficient as a function of concentration, among others, and their contrast with experimental data.References[1] Laaziri, Khalid, et al. Physical review letters 82.17 (1999):3460.[2] Fan, Feifei, et al. Modelling and Simulation in Materials Science and Engineering 21.7 (2013)074002.