Rotational disorder in lithium borohydride

Abstract

Abstract. LiBH 4 has been discussed as a promising hydrogen storage material and as a solid-state electrolyte in lithiumion batteries. It contains 18.5 wt% hydrogen and undergoes a structural phase transition at 381 K which is associated with a large increase in rotational disorder of the [BH 4 − anion in the terahertz range. The addition of LiI as well as nano-confinement favours the disordered high temperature phase and lowers the phase transition below room temperatures. The results are discussed on the basis of first principles calculations and in relation to ionic conductivity of [Li] + .

Lithium Conductivity and Ions Dynamics in LiBH4/SiO2 Solid Electrolytes Studied by Solid-State NMR and Quasi-Elastic Neutron Scattering and Applied in Lithium–Sulfur Batteries

“…Because the incoherent scattering cross section of hydrogen is much larger (80 barns) than that of any other composing atoms ( 7 Li: 0.78; 11 B: 0.22; Si: 0.015; O: 0 barns), the recorded quasi-elastic signal must originate from the motion of the hydrogen atoms. Mobilities of the ions in borohydrides have been deeply studied with a special focus on Li + and BH 4 – mobilities in macrocrystalline or nanoconfined LiBH 4 . − Reorientational mobilities, such as rotation about the twofold and threefold BH 4 – tetrahedral symmetry axes, tetrahedral tumbling, and combination of these, have been studied and documented using QENS. Confined LiBH 4 in nanoporous materials has been found to display at least two quasi-elastic components attributed to slowly and fastly reorienting anions.…”

“…Mobilities of the ions in borohydrides have been deeply studied with a special focus on Li + and BH4mobilities in macrocrystalline or nanoconfined LiBH4. [53][54][55][56][57][58][59][60][61][62][63] Reorientational mobilities such as rotation about the 2-fold and 3-fold BH4tetrahedral symmetry axes, tetrahedral tumbling and combination of those have been studied and documented using QENS. Confined LiBH4 in nanoporous materials has been found to display at least two quasielastic components attributed to slowly and fastly reorienting anions.…”

Dynamics of the Coordination Complexes in a Solid-State Mg Electrolyte

“…Characterization by means of QENS 16 has proved to be very informative for solid hydrides and resulted in many examples of the apparent connection between anion reorientational motions and cation diffusion. [17][18][19][20][21] One of the main strengths of the method is the simultaneous access to both time and spatial parameters of relaxation processes. Figure S3).…”

“…Characterization by means of QENS has proved to be very informative for solid hydrides and resulted in many examples of the apparent connection between anion reorientational motions and cation diffusion. − One of the main strengths of the method is the simultaneous access to both time and spatial parameters of relaxation processes. Thus, jump rates, diffusion coefficients for long-range and localized diffusion, jump lengths, and mechanisms of rotations (isotropical, uniaxial) can be evaluated, providing a detailed picture of stochastic molecular motions.…”

Metal (boro-) hydrides for high energy density storage and relevant emerging technologies

“…Furthermore, the intensity of the imaginary modes decreases when the halide anion fraction is increased. As a result, the disordered phase is favored, and the phase is more mechanically stable at low temperature, due to the reorientation disordering of anion which is a common behavior of [BnHn]groups as described for different systems based on borohydrides [373][374][375].…”