Role of Inter-Dopant Interactions on the Diffusion of Li and Na Atoms in Bulk Si Anodes
- PDF / 3,487,105 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 206 Views
Role of Inter-Dopant Interactions on the Diffusion of Li and Na Atoms in Bulk Si Anodes Teck L. Tan1, Oleksandr I. Malyi2, Fleur Legrain2 and Sergei Manzhos2* 1
Institute of High Performance Computing, 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632, Singapore 2
Department of Mechanical Engineering, National University of Singapore, Block EA #07-08, 9 Engineering Drive 1, 117576, Singapore Email: [email protected] ABSTRACT We explore, via density functional theory (DFT) calculations, the effect on the barrier height for Li and Na diffusion in bulk Si of the presence of an extra Li/Na atom at the neighboring tetrahedral (T) or hexagonal (H) interstitial site. For both neighboring sites, the lowest diffusion barrier height is reduced, although the magnitude of the reduction depends on the inter-atomic distance between the 2 Li/Na atoms. We further calculate the effective interaction between the 2 atoms and show that it is a strong predictor of diffusion barrier heights for both Li-Si and Na-Si systems. Importantly, the correlation between inter-dopant interaction and barrier height may be used in future work to predict the diffusion barriers at higher concentration of inserted atoms. INTRODUCTION The development of high-energy density, high-rate electrochemical batteries is key to sustainable energy development, as they will enable large-scale storage of electricity derived from intermittent sources (such as wind and solar) as well as its use to power machinery and electronics directly. Li-ion batteries provide today the highest energy density among commercial batteries (up to 200 Wh/kg at rates of fractions of 1C) at hundreds or thousands of charge/discharge cycles [1]. Special attention was devoted to studies of Si-based anode materials, as Si has one the best known capacities for Li storage [2]. The potential of Si materials for other types of batteries – such as Na-ion batteries which are most promising for bulk storage [3] – has started to receive more attention [4, 5]. Many theoretical studies to date have focused on dopantSi interactions [6-14]. Among the relevant properties computed, diffusion barrier of the dopant atoms is most directly related to the charge/discharge performance of the electrode. For bulk Si, it is known that Li/Na atoms occupy tetrahedral (T) sites at dilute concentrations and that clustering (occupation of neighboring T sites) is unfavorable but leads to a significant reduction of diffusion barriers [6, 9, 12]. It was found that single dopant atoms migrate between two T sites via the hexagonal (H) interstitial site (T→H→T). Diffusion barriers are ~0.5 eV larger for Na than for Li. However, even at low dopant concentrations, inter-dopant interactions can reduce the absolute values of migration barriers by up to 26% (and by up to 0.16/0.28 eV for Li/Na) [6]. In this work, we further investigate the effect of Li/Na occupation of a neighboring H site on the diffusion barrier. Although the occupation of a nearby H site is energetically unfavorable (compared to a T site), H sites (seco
Data Loading...
