A team of researchers from Hydro-Québec’s Center of Excellence in Transportation Electrification and Energy Storage has used plasma vapor deposition (PVD) to deposit a think Li_xSn_y alloy layer of the surface of a lithium foil. The layer has a much higher hardness than bare Li and can withstand aggressive cycling at 1C. Post-mortem scanning electron microscope observations revealed that the alloy layer remains intact even after fast cycling for hundreds of cycles.

An open-access paper on the work is published in the journal Batteries.

(a) Pieces of Li and Si are placed next to each other to deposit at the same time 400 nm of theoretical Sn by sputtering. (b) Schematic representation of the thicknesses of the layers obtained after deposition of 400 nm of Sn. While the thickness of Sn on Si is close to the theoretical value, a much thicker Sn-containing layer is clearly observed on Li substrate (about 380%) due to the formation of Li–Sn alloys. Scanning electron microscope images showing the edge of (c) silicon and (d) lithium substrates with the Sn deposit on top. Grazing angle (0.5°) X-ray diffractograms for (e) Si substrate and (f) Li foil, after deposition of 400 nm Sn by sputtering. Delaporte et al.

Recently, our research group reported the protection of Li metal foils by depositing a nanometric Zn layer with the aim of fast charging. Since the results were interesting, we tested various metals, such as Ag, Al, Sn, In, Bi, and W. After several months of investigation, it was found that the best results were obtained for the modification of lithium foils with a nanometric Sn layer.

Thus, in this work, the protection of the Li metal anode by the deposition of a thin Li_xSn_y alloy layer using the PVD technique is reported. A volume expansion of up to 380% was observed following the sputtering deposition of Sn metal. X-ray diffraction (XRD) analyses of modified Li foils revealed the disappearance of Tin peaks, which confirm the in-situ alloying reaction between the lithium anode surface and the freshly deposited Tin.

However, the exact composition of the alloy layer is not clearly determined, and it is probably composed of several Li_xSn_y alloys. Nanoindentation measurements were conducted on the Li metal before and after the deposition of Sn, and interestingly, a thin layer of Li_xSn_y alloy strongly increases the hardness of the anode, which is a desired feature to impede dendrite progression. Post-mortem scanning electron microscope (SEM) observations of used LiFePO₄ (LFP)/polymer electrolyte/Li pouch cells showed that the alloy layer remains intact even after fast cycling for hundreds of cycles.

No traces of Sn metal were found in the solid polymer electrolyte (SPE) or the Li bulk anode, and the Al additive, initially present in the Li anode, is still uniformly distributed inside it, even after repetitive cycling at high C-rates.

—Delaporte et al.

Resources

• Delaporte N, Perea A, Collin-Martin S, Léonard M, Matton J, Demers H, Clément D, Gariépy V, Zhu W. Designing a Stable Alloy Interlayer on Li Metal Anodes for Fast Charging of All-Solid-State Li Metal Batteries. Batteries. 2024; 10(7):253. doi: 10.3390/batteries10070253