Surface Modification of Lithium Metal Foil

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lithium metal foil is a soft, flexible sheet of lithium that can be rolled down to an extremely thin thickness. This material has potential applications in lithium batteries for mobile phones and other electronics, because it can be a low-cost alternative to the more expensive lithium cobalt (LiCo) and nickel manganese (NMC) electrodes currently used.

The performance of these lithium metal anodes can be dramatically improved by surface modification to suppress dendrite growth and improve ionic conductivity between the electrode and the liquid electrolyte. One such method involves spray painting the lithium surface with a soluble graphene oxide (GO) solution, which is reduced spontaneously to form a thick layer of GO on the electrode, resulting in a much smoother and tighter surface than the unmodified foil. As a result, the GO-modified foil is able to sustain flat voltage plateaus for up to 1,000 cycles in Li/Li coin cells under OCV.

A less-studied method of surface modification consists of immersing the lithium metal in a DMSO solution containing an ionically conductive polymer to form a protective layer on the electrode surface. Choi et al. showed that the ionically conductive polymer PEDOT-co-PEG was capable of inhibiting dendrite growth by providing inter-space between lithium ions, as confirmed by XPS analysis.

To demonstrate the effectiveness of this approach, the morphology and chemistry of both the as-received and roll-pressed lithium electrodes were studied in detail by AFM, SEM, and XPS. The results indicate that the roll-press treatment significantly reduces both the roughness and thickness of the native surface film on the lithium foil. The morphology of the as-received lithium is characterised by mountain- and valley-like structures, while the thinning of the native film leads to a flatter topography with fewer of these structures on the roll-pressed foil. These changes were reflected in the evolution of the SEI during cycling of Li/Li symmetric cells, with the as-received electrode exhibiting major voltage oscillations after the first cycle while the roll-pressed electrode displayed a stable chargeā€“discharge behavior for up to 70 cycles.