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Archer Group paper published in PNAS: “Hairy” Nanoparticles are the key to a more powerful and safer lithium battery

Thursday, June 14, 2018

Snehashis Choudury

Confining electrodeposition of metals in structured electrolytes

With ever-increasing demands for long-lasting and lightweight batteries, it is evident that contemporary Li-ion batteries will fall short in providing power for advanced electronics of the future. One promising pathway towards evolving the Li-ion battery involves the replacement of the graphitic anode with lithium metal. In doing so, it is possible to further utilize high capacity, Li-free cathodes like oxygen or sulfur and increase the anodic energy capacity by ten times. This can lead to pathways towards energy dense batteries required for long-range electric vehicles and grid-level storage. However, a lingering problem, associated with the metallic anodes, is uneven dendritic electrodeposition during the charging process that causes sudden short-circuits and capacity fading. There have been several studies in literature dedicated to the prevention of dendrite growth by means of a high modulus physical barrier. However, this expectation runs counter to recent experimental reports which indicate that stable, dendrite-free electrodeposition of metals can be achieved in solid/semi-solid electrolytes with mechanical moduli three or more orders of magnitude below that of the metal electrode.

In recent theoretical works, the Archer Group showed that the length-scale on which ion transport occurs near the electrodes could be as important as electrolyte modulus in stabilizing metals against dendrite formation. It was concluded that dendrites could be prevented from crossing over to the counter electrode using battery separators with pore-diameter smaller than critical (smallest) size of the dendritic nucleate. The research performed by Choudhury, Vu et. al. sought to evaluate and extend these predictions. In this study, cross-linked nanoparticle-polymer composite electrolytes with tunable pore size were designed, and their stabilities were quantified by direct visualization of electrodeposition using optical microscopy. In agreement to predictions, a critical pore-size was found; below this pore-size, the electrodeposits were confined and compact, while above this pore-size, characteristic dendritic growth was observed. The proof of electrodeposit confinement shown in this work is important for advancing battery technologies as it verifies that a polymer electrolyte, when designed with appropriate nanostructure, can simultaneously facilitate ion transport and mitigate battery short-circuit.

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