Clean Technology 2011

In-Situ Atomic Scale Visualization of Battery Charging and Discharging

J.Y. Huang
Sandia National Labs, US

Keywords: battery, nanowires, in-situ electron microscopy

Abstract:

Lithiation/delithiation of the electrode materials in Li-ion batteries (LIBs) induces large strains in the host material leading to plasticity and fracture. Lithiation is also often accompanied by phase transformations, such as electrochemically-driven solid-state amorphization (ESA). These electrochemical reaction-induced microstructural events limit the energy capacity and cycle lifetime of LIBs. It was recently reported that lithium-ion anode materials composed of nanowires can offer improved performance and lifetime compared to those of micron-scale or larger materials. The improvements are often attributed to the nanowire’s unique geometry and enhanced accommodation of the transformation strains that occur during cycling. However, the detailed mechanisms of strain-induced plasticity and strain accommodation in nanowires during electrochemical charging are largely unknown. We report the creation of a nanoscale electrochemical device inside a transmission electron microscope – consisting of a single SnO2 nanowire anode, an ionic liquid electrolyte and a bulk LiCoO2 cathode – and the in-situ observation of the lithiation of the SnO2 nanowire during electrochemical charging [1]. Upon charging, a reaction front propagated progressively along the nanowire, causing the nanowire to swell, elongate, and spiral. The reaction front is a “Medusa zone” containing a high density of mobile dislocations, which are continuously nucleated and absorbed at the moving front. This dislocation cloud indicates large in-plane misfit stresses and is a structural precursor to electrochemically-driven solid-state amorphization. Because lithiation-induced volume expansion, plasticity and pulverization of electrode materials are the major mechanical effects that plague the performance and lifetime of high capacity anodes in lithium-ion batteries, our observations provide important mechanistic insight for the design of advanced batteries. References 1. J.Y. Huang et al., Science 330, 1515-1520 (2010); Y. M. Chiang, Science 330, 1485 (2010
 

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