Importance of Halide Ions in the Stabilization of Hybrid Sn-Based Coatings for Lithium Electrodes.

The properties of hybrid Sn-based artificial solid electrolyte interphase (SEI) layers in protecting Li-metal electrodes toward surface instabilities were investigated via a combined experimental and theoretical approach. The performance of coating layers can be coherently explained based on the nature of the coating species. Notably, when starting from a chloride precursor, the hybrid coating layer is formed by an intimate mixture of Li7Sn2 and LiCl: the first ensures a high bulk ionic conductivity, while the second forms an external layer allowing a fast surface diffusion of Li+ to avoid dendrite growth, a low surface tension to guarantee the thermodynamic stability of the protective layer, and a negative underneath plating energy (UPE) to promote lithium plating at the interface between the Li metal and the coating layer. The synergy between the two components and, in particular, the crucial role of LiCl in the promotion of such an underneath plating mechanism are shown to be the key properties to improve the performance of artificial SEI layers.

Glycerol-plasticized agarose separator suppressing dendritic growth in Li metal battery.

The growth of dendrite is the major limitation to the development of the Li-metal battery. To solve it, we disclose the preparation and performances of separator (MAGly) with a complete "green" formulation using biosourced and sustainable compounds: agarose as biopolymer along with glycerol as plasticizing agent. The natural biopolymer films are non-porous in nature and possess high elasticity with high stiffness along a wide temperature range (-35 to 180 °C), able to prevent the perpendicular dendritic Li growth. Moreover, they provide high Li+ ionic conductivity, which was evident from electrochemical symmetrical battery tests resulted in efficient plating/stripping of Li metal, without dendrite formation. Preliminary tests in Li battery, with LiFePO4 as positive electrode show very satisfying performance regarding the same test with the commercial Celgard® separator. Furthermore, the application of this new sustainable separator can be extended to post Li-metal system as demonstrated by the electrochemical tests realized with K+/K.

Effect of the electrolyte on K-metal batteries.

The comparison of different electrolytes showed that both salt concentration and anion are key parameters for controlling the performance of K-metal batteries. Among the different tested electrolytes, 5 M KTFSI in DME exhibits the best stability at high potential and good performance in K|Prussian blue cells.