Tuesday, 30 May 2017: 15:20
Grand Salon D - Section 24 (Hilton New Orleans Riverside)
Rechargeable lithium-ion batteries are one of the most used devices for energy storage but still a lot of researcher needs to be performed to improve their cycling and storage capacity. The most used material anodes is graphite with a theoretical capacity of 372 mAh/g. Thus, silicon have been proposed as an anode material because its large capacity of 3,579 mAh/g. Several experimental and theoretical-computational works have been done to find out how silicon behaves during lithiation (charging of the battery), especially when the silicon anode increases its volume up to 300% due to the lithiation process. In order to understand the mechanics and chemistry of silicon electrodes and to prevent undesirable effects such as the cracking of the anode, research have been performed on nanoscale approaches to a fully nanobattery. We study both, the graphite and the silicon nanocrystal anodes, performing molecular dynamics atomistic simulations. In this effort in progress we are focusing on the mechanical properties, such as swelling, alloying mechanism, and amorphization of the anode material during the first charging cycle and also the electrical properties such as polarization and current. The nanobattery includes LiCoO2 cathode; the electrolyte solution contains ethylene carbonate, as well as hexafluorophosphate and Li-ions. In these preliminary models, a solid electrolyte interface (SEI) is not included yet. An external electric field is applied to emulate the charging process causing the migration of the Li-ions from the cathode, diffusing through the electrolyte to finally get into the anode. We immediately observe during charging (i.e., when an external electric field is applied) of the nanobattery, the Si anode changes gradually into a LiSi alloy at temperatures below 360 K, using an NVT ensemble. We obtained the drift velocity of the Li-ions during the amorphization of the silicon nanocrystal as the original volume of the anode increases. For the graphite anode, the full lithiated state is achieve when the initial structure C changes into LiC6, storing the Li-ion between the layers of the graphite, thus we were able to compare energy, temperature, and electrical properties such as current, resistance, current density, conductivity and resistivity. Our model can be used to study the mechanisms taking place in the electrolyte, cathode, and especially for new materials for the anode.