EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Solid-state electrolytes (SSEs) are promising candidates for resolving the intrinsic limitations of the organic liquid electrolyte currently employed in Li-ion batteries. Complex hydrides (e.g. LiBH4) are suggested as solid-state electrolytes. Among the different polymorphs of LiBH4, only the hexagonal phase, which is stable at temperatures above 110°C, has a remarkable high ionic conductivity (~10-3 S/cm at 120 °C). To practically access a room temperature (RT) SSB, a promising approach to enhance the Li-ion conductivity of LiBH4 at RT is the development of high conductive interface by mixing it with oxide (such as SiO2, and MgO).
In this work the Li-ion conductivity of LiBH4 has been enhanced by means of MgO-mixing. The optimum composition of the mixture demonstrated a Li-ion conductivity of 2.86 10-4 S/cm at 20 °C. The improved Li-ion conductivity relies on the formation of a conductive interface that can be described by a core-shell model where the fraction of LiBH4 (the core) is in direct contact with the oxide (the shell).
The formation of the composite does not affect the electrochemical stability window, which is similar to that of pure LiBH4 (about 2.2 V vs. Li+/Li). The mixture has been incorporated as solid-electrolyte in a TiS2/Li all-solid-state Lithium metal battery. A freshly prepared battery failed at RT only after 5 cycles. On the other hand, a stable solid electrolyte interphase can be obtained by a pre-conditioning cycling at 60 °C. Afterward, a capacity retention of about 80 % at the 30th cycle was obtained operating at RT. We illustrate that the addition of oxide nanoparticles to LiBH4 offers a promising strategy to obtain novel SSE candidates for Li-based SSB.