First principles and experimental studies of empty Si 46 as anode materials for Li-ion batteries
- PDF / 521,359 Bytes
- 9 Pages / 584.957 x 782.986 pts Page_size
- 101 Downloads / 215 Views
Candace K. Chan Materials Science and Engineering, School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ 85287-8706, USA (Received 12 July 2016; accepted 19 October 2016)
The objective of this investigation was to utilize the first-principles molecular dynamics computational approach to investigate the lithiation characteristics of empty silicon clathrates (Si46) for applications as potential anode materials in lithium-ion batteries. The energy of formation, volume expansion, and theoretical capacity were computed for empty silicon clathrates as a function of Li. The theoretical results were compared against experimental data of long-term cyclic tests performed on half-cells using electrodes fabricated from Si46 prepared using a Hofmann-type elimination–oxidation reaction. The comparison revealed that the theoretically predicted capacity (of 791.6 mAh/g) agreed with experimental data (809 mAh/g) that occurred after insertion of 48 Li atoms. The calculations showed that overlithiation beyond 66 Li atoms can cause large volume expansion with a volume strain as high as 120%, which may correlate to experimental observations of decreasing capacities from the maximum at 1030 mAh/g to 553 mA h/g during long-term cycling tests. The finding suggests that overlithiation beyond 66 Li atoms may have caused damage to the cage structure and led to lower reversible capacities.
I. INTRODUCTION
Silicon is an attractive anode material for Li-ion batteries because its theoretical charge storage capacity (3579 mAh/g as Li15Si4) is more than 10 times than that of graphite,1 the current anode material in commercial cells. Despite a high theoretical charge capacity, silicon has not been successfully utilized as the anode in Li-ion batteries because the reversible reaction of lithium with silicon is accompanied by large (;300%) changes in volume. The large increase in volume, which is isotropic in amorphous Si, can cause Si particles to displace and impinge on other parts of the anode.2 Such particle motion has been directly observed using in situ atomic force3 and optical microscopes.4 Theoretical studies on electrodes made of Si particles have found that in order for the particles to be adequately spaced to avoid displacement, they must occupy only 20 vol% of the electrode, whereas the remaining mass consists of the binder and conducting additives.5 This composition leads to a serious reduction in energy density because the active Si material makes up only a small percentage of the electrode.
Contributing Editor: Chongmin Wang a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.408
Furthermore, the large volume mismatch between the unlithiated and lithiated phases often results in large internal stresses6 that cause the Si to delaminate from the electrode (decrepitation) or form smaller particles (pulverization) that are detached from the current collector. Mixing or ball-milling the Si with binders or other networking agents (such as carbon nanotubes7–9) hav
Data Loading...
