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Postdoctoral program guidelines

Biedermann, Laura B.; Teich-McGoldrick, Stephanie T.; Cruz-Campa, Jose L.; Ekoto, Isaac W.; Ferreira, Summer R.; Hall, Lisa M.; Liu, Xiaohua L.; Liu, Yanli L.; Sava Gallis, Dorina F.

We, the Postdoc Professional Development Program (PD2P) leadership team, wrote these postdoc guidelines to be a starting point for communication between new postdocs, their staff mentors, and their managers. These guidelines detail expectations and responsibilities of the three parties, as well as list relevant contacts. The purpose of the Postdoc Program is to bring in talented, creative people who enrich Sandia's environment by performing innovative R&D, as well as by stimulating intellectual curiosity and learning. Postdocs are temporary employees who come to Sandia for career development and advancement reasons. In general, the postdoc term is 1 year, renewable up to five times for a total of six years. However, center practices may vary; check with your manager. At term, a postdoc may apply for a staff position at Sandia or choose to move to university, industry or another lab. It is our vision that those who leave become long-term collaborators and advocates whose relationships with Sandia have a positive effect upon our national constituency.

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TYPE SAND Report YEAR 2012
OSTIDOI

In situ atomic-scale imaging of electrochemical lithiation in silicon

Nature Nanotechnology

Liu, Xiaohua L.; Wang, Jiang W.; Huang, Jian Y.; Fan, Feifei; Huang, Jian Y.; Liu, Yang; Krylyuk, Sergiy; Yoo, Jinkyoung; Dayeh, Shadi A.; Davydov, Albert V.; Mao, Scott X.; Picraux, S.T.; Zhang, Sulin; Li, Ju; Zhu, Ting; Huang, Jian Y.

In lithium-ion batteries, the electrochemical reaction between the electrodes and lithium is a critical process that controls the capacity, cyclability and reliability of the battery. Despite intensive study, the atomistic mechanism of the electrochemical reactions occurring in these solid-state electrodes remains unclear. Here, we show that in situ transmission electron microscopy can be used to study the dynamic lithiation process of single-crystal silicon with atomic resolution. We observe a sharp interface (∼1 μnm thick) between the crystalline silicon and an amorphous Li x Si alloy. The lithiation kinetics are controlled by the migration of the interface, which occurs through a ledge mechanism involving the lateral movement of ledges on the close-packed {111} atomic planes. Such ledge flow processes produce the amorphous Li x Si alloy through layer-by-layer peeling of the {111} atomic facets, resulting in the orientation-dependent mobility of the interfaces. © 2012 Macmillan Publishers Limited. All rights reserved.

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TYPE Journal Article YEAR 2012
ScopusOSTIDOI

Real-time studies of battery electrochemical reactions inside a transmission electron microscope

Sullivan, John P.; Huang, Jian Y.; Leung, Kevin L.; Fan, Hongyou F.; Liu, Xiaohua L.; Hudak, Nicholas H.

We report the development of new experimental capabilities and ab initio modeling for real-time studies of Li-ion battery electrochemical reactions. We developed three capabilities for in-situ transmission electron microscopy (TEM) studies: a capability that uses a nanomanipulator inside the TEM to assemble electrochemical cells with ionic liquid or solid state electrolytes, a capability that uses on-chip assembly of battery components on to TEM-compatible multi-electrode arrays, and a capability that uses a TEM-compatible sealed electrochemical cell that we developed for performing in-situ TEM using volatile battery electrolytes. These capabilities were used to understand lithiation mechanisms in nanoscale battery materials, including SnO{sub 2}, Si, Ge, Al, ZnO, and MnO{sub 2}. The modeling approaches used ab initio molecular dynamics to understand early stages of ethylene carbonate reduction on lithiated-graphite and lithium surfaces and constrained density functional theory to understand ethylene carbonate reduction on passivated electrode surfaces.

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TYPE SAND Report YEAR 2012
OSTIDOI

Anisotropic Swelling and Fracture of Silicon Nanowires during Lithiation

Nano Letters

Sullivan, John P.; Liu, Xiaohua L.; Huang, Jian Y.

We report direct observation of an unexpected anisotropic swelling of Si nanowires during lithiation against either a solid electrolyte with a lithium counter-electrode or a liquid electrolyte with a LiCoO2 counter-electrode. Such anisotropic expansion is attributed to the interfacial processes of accommodating large volumetric strains at the lithiation reaction front that depend sensitively on the crystallographic orientation. This anisotropic swelling results in lithiated Si nanowires with a remarkable dumbbell-shaped cross section, which develops due to plastic flow and an ensuing necking instability that is induced by the tensile hoop stress buildup in the lithiated shell. The plasticity-driven morphological instabilities often lead to fracture in lithiated nanowires, now captured in video. These results provide important insight into the battery degradation mechanisms.

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TYPE Journal Article YEAR 2011
OSTIDOI
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