Computational study of Mg insertion into amorphous silicon: advantageous energetics over crystalline silicon for Mg stor
- PDF / 6,146,022 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 154 Views
Computational study of Mg insertion into amorphous silicon: advantageous energetics over crystalline silicon for Mg storage Fleur Legrain1, Oleksandr I. Malyi1, Teck L. Tan2, and Sergei Manzhos1 1
Department of Mechanical Engineering, National University of Singapore, Block EA #07-08, 9 Engineering Drive 1, 117576, Singapore 2
Institute of High Performance Computing, 1 Fusionopolis Way, #16-16 Connexis, 138632, Singapore Email: [email protected] ABSTRACT We show in a theoretical density functional theory study that amorphous Si (a-Si) has more favorable energetics for Mg storage compared to crystalline Si (c-Si). Specifically, Mg and Li insertion is compared in a model a-Si simulation cell. Multiple sites for Mg insertion with a wide range of binding energies are identified. For many sites, Mg defect formation energies are negative, whereas they are positive in c-Si. Moreover, while clustering in c-Si destabilizes the insertion sites (by about 0.1/0.2 eV per atom for nearest-neighbor Li/Mg), it is found to stabilize some of the insertion sites for both Li (by up to 0.27 eV) and Mg (by up to 0.35 eV) in a-Si. This could have significant implications on the performance of Si anodes in Mg batteries. INTRODUCTION The development of high-power energy density and high-rate electrochemical batteries is key to sustainable development. They will enable large-scale storage of electricity derived from intermittent sources (such as wind and solar) as well as their use to directly power machinery and electronics. 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], but even higher energy density and / or charge / discharge rates will be needed to achieve requirements for all-electric vehicles and bulk storage. For high energy density applications, Mg is a promising alternative to Li. Mg is divalent and cheaper and more abundant than Li, of which the deposits and their geographic distribution may not be compatible with massive-scale battery applications [2]. Commercialization of Mg-ion batteries is believed to be possible in the near future [3], but their good cyclability remains a problem. Reactions between anode and electrolyte are one of reasons for this. While development of new electrolytes is one way to alleviate this issue [4], the development of alternatives, specifically insertion type anodes, is also important for making Mg-ion batteries a viable commercial technology [5-7]. Computational studies are necessary for the rational design of prospective anode materials. Among prospective anode materials for metal-ion batteries, Si has emerged as a very high capacity anode for Li-ion batteries [8] and has been considered for Na and Mg-ion batteries [7, 9-11]. It has been shown that the theoretical capacity of Si for Mg-ion batteries (3817 mAh/g) [7] is comparable to that of Li-ion batteries (4200 mAh/g) [8]. Most theoretical studies to date focused on c-Si (diamond structure) [7, 9-14].
Data Loading...
