Stabilizing lithium and sodium fast-ion conduction in solid polyhedral-borate salts at device-relevant temperatures

Abstract

By a variety of techniques including X-ray powder diffraction, quasielastic neutron scattering, and AC impedance, we have probed the effect of mechanical milling on the phase behaviors of the different lithium and sodium closo-borate salt compounds containing B 12 H 12 2-, B 10 H 10 2-, and CB 11 H 12anions. We have found that the crystallite-size reduction and disordering effects of such milling enables the room-T stabilization of their high-T-like superionic-conducting phases. This demonstrates a viable strategy for better exploiting the impressive cation mobilities that are typically restricted to somewhat higher temperatures for this class of compounds.

Comparison of Anion Reorientational Dynamics in MCB9H10 and M2B10H10 (M = Li, Na) via Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Studies

“…Note that in the case of Na 2 B 12 H 12 , the agreement between the E a values for anion reorientations in the disordered phase derived from NMR and QENS was very good. 7,8,15 We may take into account that for M 2 B 10 H 10 and MCB 9 H 10 , the temperature ranges used for evaluation of the activation energies for QENS data are broader than those for NMR data; in this respect, the QENS results should be considered as more reliable. On the other hand, if certain distributions of the reorientational jump rates are present in the disordered phases, a straightforward analysis of QENS data may underestimate the actual activation energies, as explained in ref 35.…”

“…Although the order−disorder transition to superionic behavior is often above room temperature for the closoborate-based salts (see Table S1 in the Supporting Information for a list of transition temperatures of Li and Na closo-borate salts), these disordered phases can be stabilized at and below room temperature by proper chemical or morphological modifications. 4,15,16 Obtaining any detailed fundamental understanding of the reorientational dynamics of these hydrogenous complex anions requires appropriate experimental probes, two prime candidates being nuclear magnetic resonance (NMR) and incoherent quasielastic neutron scattering (QENS). Indeed, NMR and QENS are well-known for providing complementary microscopic information on hydrogen jump motion in materials.…”

Reorientational motion and Li+ -ion transport in Li2B12H12 system: M

“…Among the various materials reported to date, complex borohydrides are considered outstanding potential candidates for the solid electrolyte in SSBs because of the high Li-or Na-ion conductivity (exceeding 10 −1 S cm −1 ) [12][13][14][15][16][17][18][19][20], which enables a wide range of chemical substitutions and opens up the possibility of searching for even better ion-conductive materials. The general form of metal borohydrides is written as M x (M y H z ), where M can be replaced by alkali or alkaline-earth atoms.…”

Bulk-Type All-Solid-State Lithium Batteries Using Complex Hydrides Containing Cluster-Anions

“…31) In addition, we recently discovered that when Na 2 B 12 H 12 powder is aggressively ball-milled, the crystals become nanometer scaled, which results in the disappearance of the conductivity jump accompanied by the phase transition. 29) As a result, ball-milled Na 2 H 12 H 12 possessed high sodium ionic conductivity of log(σ/S cm −1 ) = −3.8 at room temperature, as shown in Fig. 1.…”

“…As a result, over 300 dischargecharge cycles were successfully demonstrated. 18) We explored a series of complex hydrides having a cluster anion as a novel electrolyte design guide, and discovered various fast lithium 26,27) and sodium ionic conductors; [26][27][28][29][30] the ionic conductivities of a selection of these compounds are shown in Fig. 1.…”