Fast-ionic conductivity of Li+in LiBH4

Abstract

High Li + conductivity in the high-temperature (hexagonal) phase of LiBH 4 is revealed through a first-principles molecular dynamics simulation of 1200 atoms using periodic boundary conditions. The high ionic conductivity originates from the generation of a Li + metastable state located at an interstitial site surrounded by three Li + ions and three BH − 4 ions in the a-b plane. A defect is created by Li + ions hopping from their original sites to this interstitial site. The defect then diffuses through a path connecting the nearby Li sites separated in the a and c directions. Coupling of these movements is observed. The double splitting of the Li occupation in the original Li site plays an important role in the creation of the metastable state and migration through the connection path. The activation energy and diffusion coefficient are estimated, and are within one order of magnitude of experimentally retrieved values.

\mathcal{O}(N) methods in electronic structure calculations

“…The code has been applied to liquid ethanol [44] and a fast ion conductor [456] with stability and efficiency.…”

“…The same method has been applied to calculations of Li + conductivity in LiBH 4 [456]. Using 100 unit cells (each with two LiBH 4 units, for a total of 1,200 atoms) and localisation regions of 10 a 0 for Li and 14 a 0 for B, the CPU time was reduced by a factor of 2.5 with no reduction of accuracy.…”

Ionic conductivity and the formation of cubic CaH2 in the LiBH4–Ca(BH4)2 composite

“…All above-mentioned crystalline solid electrolytes have considerably lower Li + conductivities, with the exception of Li 10 GeP 2 S 12 which has a Li + conductivity of 12 m/S/cm at 27°C [13]. Lithium borohydride has been investigated extensively in recent years, both as a hydrogen storage material [18][19][20][21][22][23] and as a crystalline solid electrolyte material for lithium batteries [24][25][26]. It is lightweight (0.666 g/cm 3 ) and has been shown to be electrochemically stable up to 5 V [27].…”

Complex hydrides as room-temperature solid electrolytes for rechargeable batteries

“…cations and [BH 4 ] -anions, can be found in different polymorphs, depending on pressure and temperature (see Fig. 2) [24][25][26][27]. The orthorhombic phase, which is the stable phase at room temperature, has a low ionic conductivity (*10 -8 S cm -1 at 30°C).…”

“…can, with a relatively low activation barrier and probably helped by rotation of the neighbouring BH 4 -units, jump from one interstitial site to the next (see Fig. 2) [22,24,29,30]. In the LiBH 4 :LiI solid solutions, the mobilities of Li ?…”