This underscores the pivotal role played by phase transitions within this class of materials. Consequently, it is paramount to gain a comprehensive understanding of the intricacies surrounding phase transition phenomena, encompassing the underlying factors and origins. This improved conductivity in LiBH 4 arises due to the rotational disorder of the [BH 4 ] -units in the high-T phase, a unique characteristic of such materials. The cationic sites' lattice disorder contributes to the high ionic conductivity, and the rotational disorder of BH 4 units has been investigated through techniques such as synchrotron X-ray powder diffraction, quasi-elastic neutron scattering (QENS), and ab initio MD simulations . In the pursuit of maximizing ionic conductivity, various efforts have been dedicated to stabilizing the highly conductive phase at or near RT. One approach involves doping halides into LiBH 4 , resulting in compounds such as Li(BH 4 ) 1-x X x (X = Cl, Br, and I), where a RT high conducting phase is observed for x > 0.25, particularly in the case of iodine doping . Another popular strategy involves incorporating neutral molecules, such as LiBH 4 •1/2NH 3 , which also exhibit notable ionic conductivity (σ(Li + ) = 7 × 10 -4 Scm -1 at 40 • C) . A more in-depth discussion regarding the role of these neutral molecules will be presented subsequently in this section on materials.