Lithium-ion batteries (LIBs) are one of the indispensable solutions in the landscape of energy storage devices. However, these devices present some disadvantages, mainly due to the organic liquid electrolyte on which they are based. To name a few: the presence of a flammable liquid increases the risk of explosion if thermal runaway happens. Besides, the electrolyte is prone to the formation of dendrites when a metallic lithium anode is used, leading to a lower coulombic efficiency and eventually to short circuiting of the cell. In recent years the scientific community is devoted to the development of solid electrolyte to pave the distribution of All-Solid-State Batteries (ASSBs). The most proposed electrolytes were polymer based; however, a growing interest has arisen in ceramic electrolytes. Their high electric modules could reduce the dendrites penetration upon cycling and reduce the flammable risk of conventional liquid electrolytes.

Among ceramic electrolytes, three classes of materials have been recognized as promising solutions: i) oxides, ii) sulfides and iii) halides. The first class presents high mechanical strength and generally good compatibility with Li metal; however they require a sintering step at high temperature to ensure the desired density, which makes them costly to produce. Sulfide materials can be densified through cold pressing and show high ionic conductivity (around 1mS/cm), as drawback, when exposed to moisture generates toxic H₂S. Halides are a relatively new solution to be applied to solid-state batteries, as sulfides, they present high ionic conductivity and can be densified applying uniaxial pressure, and their degradation byproducts do not include toxic compounds. These qualities make halides promising candidates to be used as ceramic electrolytes in ASSBs^[1]. Nevertheless, further studies are necessary to achieve a complete understanding of the structural, morphologic, and electrochemical properties of this class of materials.

In this work we focus on a high conductive halide, Li_2.25Fe_0.25Zr_0.75Cl₆, prepared by two different routes, mechano-chemically^[2,3] and solid state synthesis. The latter showing promising morphological and electrochemical properties comparable to a high energy synthesis. This thoughtfully study, combining computational and experimental aspect will allow the production of an in-situ hybrid electrolyte to be integrated in Gen4.b ASSBs.