Molecular-salt hybrids; integration of ammonia borane into lithium halides

Abstract

New hybrids release hydrogen on decomposition and demonstrate Li-ion conductivity >100 times higher than the component salts.

Reinvestigation of ionic conductivity of a layered Li(BH3NH2BH2NH2BH3) salt

“…7LiBH4•LiI [20]; LiCe(BH4)3Cl [21]) remain HT-LiBH4 crystal structure below 115°C, showing high conductivity at RT (4.5×10 -5 S/cm [20]; 1.0×10 -4 S/cm [21]). [26], (LiBH4)(NH3BH3) [23], (LiBH4)2(NH3BH3) [23], (LiI)(NH3BH3) [24], (LiI)(NH3BH3)2 [24]. Below, coordination spheres of lithium cations with Li-B and Li-I distances.…”

“…Below, coordination spheres of lithium cations with Li-B and Li-I distances. For clarity of visualisation, Li coordination spheres are shown with no distortion of (B3N2)anions in Li[B3N2] [26] and Li + cations in (LiI)(NH3BH3)2 [24].…”

“…However, adducts of LiBH4 with molecular ammonia borane were reported to show very high conductivity at 40°C: (LiBH4)(NH3BH3) 4.9x10 -3 S/cm and (LiBH4)2(NH3BH3) 1.2×10 −4 S/cm [23]. Recently, Cascallana-Matías et al reported ammonia borane adducts related materials exhibiting high lithium conductivity at 70°C: (LiBH4)2(NH3BH3) 2.83×10 −5 S/cm, (LiI)(NH3BH3) 1.80×10 −6 S/cm and (LiI)(NH3BH3)2 1.79×10 −5 S/cm, while Li(BH3NH2BH2NH2BH3) was claimed to have much poorer conductivity of 4.11×10 −9 S/cm at 70°C [24]. Surprisingly, the figure for Li(BH3NH2BH2NH2BH3) was as low as conductivity of Li(NH2BH3) (5.5×10 -9 S/cm at RT [22]) having unfavourable crystal structure with neither 1D nor 2D lithium cations substructure.…”

KB3H8·NH3B3H7 Complex as a Potential Solid-State Electrolyte with Excellent Stability against K Metal

“…46−48 For example, the volume expansion of LiBH 4 •AB has four times larger cell volume and delivers nearly 4 orders of magnitude higher Li-ion conductivity at room temperature than LiBH 4 . 49,50 Mg(BH 4 ) 2 •2AB has one of the highest solid-state Mg-ion conductivities reported to date according to the increased Mg−B bond distance, the enlarged volume of the tetrahedron surrounding Mg, and the potential distortion of this tetrahedron in the crystal structure. 46 This neutral molecule incorporation approach should have wide applicability to other analogues, for example, KB 3 H 8 .…”

“…Besides, as the improvement of synthetic methods, − KB 3 H 8 and KB 11 H 14 have also been investigated as new low-cost K-ion SSEs and display ionic conductivities of 3.4 × 10 –7 and 1.2 × 10 –4 S cm –1 at 150 °C, respectively. , Further improvement in ionic conductivity is necessary for borohydride-based K-ion SSEs. So far, many structural tuning approaches such as second-phase incorporation, chemical modification, addition of interphase composition, and nanoconfinement in mesoporous scaffolds have been successfully developed to improve the ionic conductivity of borohydrides. , Among these approaches, incorporation of a neutral molecule NH 3 or NH 3 BH 3 (AB) into M­(BH 4 ) n (M = Li, Mg; n = 1, 2) is often helpful because of the more mobile cations in the M­(BH 4 ) n ·NH 3 or M­(BH 4 ) n ·AB complexes. − For example, the volume expansion of LiBH 4 ·AB has four times larger cell volume and delivers nearly 4 orders of magnitude higher Li-ion conductivity at room temperature than LiBH 4 . , Mg­(BH 4 ) 2 ·2AB has one of the highest solid-state Mg-ion conductivities reported to date according to the increased Mg–B bond distance, the enlarged volume of the tetrahedron surrounding Mg, and the potential distortion of this tetrahedron in the crystal structure . This neutral molecule incorporation approach should have wide applicability to other analogues, for example, KB 3 H 8 .…”