In lithium-ion batteries, Si-based materials such as silicon alloys are regarded as a promising alternative to graphite negative electrode to achieve higher energy. Unfortunately, they often suffer from a large volume change that can result in poor cycle life. We monitored the electrode expansion/contraction that occurs during lithiation/delithiation in real time by electrochemical dilatometry. Volume changes of Si alloy-based electrode with three different polymer binders have been compared. Electrode manufactured with lithiated polyacrylic acid (LiPAA) exhibited the greatest expansion but also demonstrated the highest reversibility as well as the best cycling performance. Ex situ SEM imaging along with dilatometer measurements revealed that electrode porosity after contraction (delithiation) increases compared to that after precedent expansion (lithiation), which can buffer volume expansion at the subsequent cycle. Proof-of-concept in situ optical microscopy (IOM) experiments were carried out with the best performing LiPAA electrode. The results demonstrated that LiPAA electrode in the IOM cell expanded much less than the same electrode in the dilatometer cell. This implies that internal pressure existing in a lithium-ion cell has a great impact on total electrode expansion.

Stochastic dynamics simulations of n-alkane melts (C13H28 and C28H6g) confined between solid surfaces have been performed in order to study the influence of the surface structure and interactions on the structural and dynamic properties of the chain molecules at the interfaces. Moreover, these simulation results have been compared with the predictions of the Scheutjens -Fleer lattice theory in order to investigate the general applicability of the theory in predicting the conformational properties of real (atomistic) melt chains at the interfaces. The n-alkane chains are described as mass points (united atoms) linearly connected by rigid bonds and subjected to bond bending, torsional, and nonbonded interaction potentials. For repulsive surfaces, an atomistic, ordered surface was found to yield the same static and dynamic properties of the chains as a flat, structureless surface. The presence of a strongly attractive surface was found to increase layering of both monomers and entire n-alkane molecules at the surface. Chains with only ends strongly attractive to the surfaces (sticky ends) exhibited an increased probability of long tails and loops and a decreased probability of long trains. However, no significant change in the strong preference for trains comprised of entire molecules was seen. Comparison of neutral surface and sticky end simulations with Scheutjens-Fleer self-consistent-field lattice theory predictions revealed that the theory reproduces quite well the behavior of tails, loops, and trains seen from atomistic simulations of C28H58.

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Fluoroethylene carbonate (FEC) is known to be an effective electrolyte additive in silicon-based anodes for lithium ion batteries, but reported to be consumed, eventually resulting in a sudden capacity fade. We quantified the amount of remaining FEC in separators harvested from the cycled cells using infrared (IR) spectroscopy. FEC is linearly depleted over cycles until complete consumption. When the amount of FEC additive is nearly zero, capacity of the cell suddenly drops. It is first shown that IR spectroscopy is a facile method for quantitative analysis of electrolyte additives.

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