The influence of electrolyte composition and current collector morphology on the properties of anodeless lithium metal batteries

Among all the possibilities for next-generation rechargeable batteries, lithium metal is still craved as the Holy Grail of negative electrode materials, for the high theoretical specific capacity, the lowest redox potential, and the superior energy density with respect to currently used Li-ion batteries. Such energy density can be further increased by studying the anodeless configuration: the cell setup consists of a bare copper current collector where the lithium is plated directly from the cathode. Unfortunately, lithium plating/stripping on high-area surfaces displays a series of well-known problems: unstable SEI, dendrites formation that leads to cell short-circuit, and dead-lithium formation that causes severe capacity fading. In this respect, a lot of interesting strategies have been proposed; the ones adopted in this study are the electrolyte design and the employment of engineered current collectors. For this research, the effect of three different liquid electrolytes was studied on symmetrical Li|Li coin cells: commercial LP30, a Deep Eutectic Solvent and a Dual Salt electrolyte have been employed in the first part. while using the commercial LP30 and the DES the cell overpotential escalates as the cycles increase, with the DS the cyclic potential profile remains stable between ±0.02 V even after 200 cycles, confirming the validity of such electrolyte in the formation of a stable SEI. SEM measurements of the plated lithium surfaces have confirmed this stabilizing effect and its repercussions on the lithium morphology. In the second part, the DS performance has been measured in a non-symmetrical configuration to study the effect of the current collector: Cu|Li coin cells have been used for anodeless plating and stripping. As preliminary measurements, both the smooth and the rough sides of a plain Cu foil have been tested; the coins with rough Cu have displayed the most stable potential profiles and the highest Coulombic efficiencies. This is believed to be a hint of the positive effect of an irregular Cu surface.