LiBH4 as candidate solid state electrolyte in Li-ion batteries

Electrical Energy Storage (EES) systems aspire to store the power network’s energy and provide it back when necessary, eliminating the discrepancies between demand and supply. During the last decade, lithium-ion batteries have been established as an important pillar in humanity’s effort, not only to produce “cleaner power” but, also, to develop a safe, environmentally friendly and low-cost set of methods and technologies for storing the produced power. They are -by far- the most common medium for storing energy, at a small scale (e.g. portable electronics), as one of their numerous advantages is the fact that they can be used in conjunction with many different installations of the existing grid’s infrastructure. Focusing, mainly, on the mechanisms that apply in the solid-state, Li-ion conduction in Li-ion batteries takes place due to the defects existing in their crystalline solid components. Today, concerns that relate to safety, cost, charge/discharge rates, cycle life and energy density of Li-ion batteries have risen questions which need to be answered. During the last two decades, high-end research has been conducted aiming to address the challenges and limitations of lithium metal batteries (LMBs) presented previously. The ongoing efforts focus on the suppression of lithium dendritic growth, either through the use of solid electrolytes that act as mechanical barriers, or through development of electrolytes which produce a suitable passivation layer, widely known as the “solid-electrolyte interphase” (SEI). Nowadays, safety concerns have led to the extensive use of lithium-ion batteries (LIBs), rather than LMBs, as no entirely successful strategy has been developed to suspend the growth of dendrites. Complex hydrides are among the most promising candidate materials for use as solid-state electrolytes. As the demand for energy storage systems that are compact, lightweight, and powerful continues to grow, mainly due to the worldwide proliferation of portable electronic devices. Sodium, lithium and boron are the lightest elements that can form solid-state compounds with hydrogen, such as LiBH4. Researchers’ interest into the properties of lithium borohydride (LiBH4) first arose due to indications that it could function as a promising hydrogen storage material. Following its extensive study as a hydrogen storage material, LiBH4 has drawn interest as a potential electrolyte for solid-state batteries. This was proposed by the discovery that LiBH4 undergoes a structural transition from its orthorhombic, low temperature (LT-) phase to a hexagonal, high temperature (HT-) phase at 380 K. Following the stabilisation of the HT-phase at room temperature (RT), attempts have been made to synthesise sodium-substituted lithium borohydride but, previous work has suggested that a direct reaction between LiBH4 and NaBH4 is not possible. This project had been focused on the stabilisation of the high pressure (HP-) phase of LiBH4 at RT. Our efforts have been successful in the investigation of the most simple and efficient way to synthesise, stabilise and characterise the ion conducting, HP-phase of LiBH4