Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Maria Chan Project Name: CEES-Si Division: CNM Project title: Investigations of silicon surfaces and interfaces for lithium ion batteries Associated funding: DOE Energy Frontier Research Center -- Center for Electrical Energy Storage (CEES) Other Systems: CNM Carbon Science: This project uses density functional theory (DFT) to investigate silicon as an anode material for lithium ion batteries. Silicon is under intense study as an alternative to carbon-based anode materials due to enhanced safety and superior capacity. The Center for Electrical Energy Storage (CEES), an Argonne-based DOE Energy Frontier Research Center, is heavily invested in the study of Si anodes. The lithiation of crystalline Si results in vast structural changes, in contrast to graphitic electrode materials in which Li is inserted into fixed sites, with limited structural distortions. At room temperature, lithiation transforms crystalline Si into amorphous lithiated silicides LixSi. This renders traditional techniques to model battery materials, based on total energy calculations of crystalline phases, inadequate. In the previous FY, we have developed a new approach to sample configurations of LixSi which is connected to crystalline Si by Li insertion or subsequent removal, which allows us to understand the atomistic nature of the non-equilibrium reaction. Using this newly-developed configurational-sampling technique and Fusion allocation from the previous FY, we have developed an understanding of the drastic anisotropy [1] observed in the lithiation of crystalline Si micro- and nano-structures. In addition, we have also explained the effects of dopants on the lithiation behaviors [2] and investigated the large differences between Si and Ge in terms of anisotropy and dopant effects [3]. Following these successes, we are planning to continue the investigation of Si nanostructures, as well as surface and interfacial chemistries, both of which have been demonstrated experimentally to strongly affect electrochemical performance. The use of nanostructures, such as nanowires, is known experimentally to improve the cycleability of Si, presumably due to effective strain relaxations. The atomistic mechanism of such relaxations, however, is not well known. From our previous studies, we have preliminary findings on the expansion of Si nanowires upon lithiation, but found a profound effect of the lack of surface passivation on the lithiation process. Since then we have established proper surface passivation procedures and are poised for a more systematic study of various nanowire orientations and sizes. Nanoparticles are also heavily used in experimental studies and the effects of sizes on lithiation behavior is also of interest. In addition, surface and interfacial chemistries play a crucial role in the cycling performance of Si. We have identified several organic surface species that are of relevance, and would also like to investigate the effect of products of surface-electrolyte interphases, such as fluorides and carbonates, on the lithium insertion and removal mechanism. [1] M. K. Y. Chan, C. Wolverton, and J. Greeley, “First Principles Simulations of the Electrochemical Lithiation and Delithiation of Faceted Crystalline Silicon," Journal of the American Chemical Society, accepted 2012. [2] B. Long, M. K. Y. Chan, J. Greeley and A. Gewirth, “Dopant Modulated Li Insertion in Si for Battery Anodes,” Journal of Physical Chemistry C, doi:10.1021/jp2060602, (2011). [3] M. K. Y. Chan, B. Long, A. Gewirth and J. Greeley, “The first-cycle electrochemical lithiation of crystalline Ge and Si – a comparison,” in preparation. Project description: Lithiation simulations by configurational sampling – total-energy DFT calculations For (a) Si nanowires of [100], [110] and [111] orientations and diameters 1-2 nm, (b) Si nanoparticles of diameters 1-2 nm, (c) Si (111) surfaces with organic passivating species CH3, OCH3 and SCH3, and (d) interfaces of Si with solid-electrolyte interphase products LiF and Li2CO3, we will carry out lithiation simulation calculations using our newly-developed configurational sampling algorithm. This involves total-energy DFT calculations and relaxations of a series of configurations with Li inserted into interstitial sites, with the lowest-energy relaxed configuration serving as a starting point for next Li insertion. The computational costs per sampling calculation are: (a) 20-80 core-hours, (b) 40-100 core-hours, (c) 10-20 core-hours, and (d) 20-40 core-hours. The number of calculations involved is 200-2000 for each starting configuration. The total core-hours requested for the above categories are: (a) 200,000, (b) 100,000, (c) 20,000 and (d) 80,000 core-hours. Using the projector-augmented wave method, only valence electrons will be included which reduces computational costs. We will use well-established DFT codes VASP, which use a plane wave basis set. For large systems such as nanostructures, VASP has been tested on Fusion for computation involving systems with up to 7000 electrons on up to 512 cores. For routine surface calculations, hard scaling efficiency of 70%-80% has been demonstrated for 64 to 128 cores compared to 8 cores, thus enabling efficient calculations of large numbers of configurations. Please note that this renewal proposal consists of some work in the previous proposal that has been delayed due to a change in position and responsibilities as well as medical leave. Project URL: http://www.anl.gov/energy-storage-science/ Current FY Hours Used: undetermined amount New FY Requested allocation: 400000 Q1: 100000 Q2: 100000 Q3: 100000 Q4: 100000 Justification: Thank You, The LCRC Accounts System