Fast Lithium-Ion Conduction in Atom-Deficient closo-Type Complex Hydride Solid Electrolytes

Abstract

closo-type complex hydrides contain large cage-type complex polyanions in their crystal structures and thus can exhibit superior ion-conducting properties (e.g., Li and Na). However, the unique structures of complex polyanions have made it challenging to modify crystal structures, making systematic control of ion conductivity difficult. Here, we report an atom deficiency approach to enhance lithium-ion conductivity of complex hydrides. We find that lithium and hydrogen could be simultaneously extracted from Li2B12H12 by applying a small external energy, enabling the formation of atom deficiencies. These atom deficiencies lead to an increase in carrier concentration, improving lithium-ion conductivity by 3 orders of magnitude compared to that of a pristine material. An all-solid-state TiS2/Li battery employing atom-deficient Li2B12H12 as a solid electrolyte exhibits superior battery performance during repeated discharge–charge cycles. The current study suggests that the atom deficiency can be a useful strategy to develop high ion-conducting complex hydride solid electrolytes.

Complex Hydrides for Energy Storage, Conversion, and Utilization

“…By contrast, both Li 2 B 10 H 10 and Li 2 B 12 H 12 have much higher transition temperatures in excess of 600 K, restricting their high ionic conductivities. Recently, however, it was found that the ball milled Li 2 B 12 H 12 sample showed an exceptionally high ionic conductivity of 3.1 × 10 −4 S cm −1 at room temperature . It was suggested that such an enhancement was related to the effect of borane impurities present in the sample via mechanochemical treatment, leading to mixed borane disordered phase with high ionic conductivity 1b…”

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.…”

“…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. Typical complex M y H z anions include BH − 4 [21,22], B 6 H 6 2− , B 10 H 10 2− , CB 9 H 10 − , B 12 H 12 2− , and CB 11 H 12 − [19]. Among the cations, lithium-ion electrolytes are a key component of all SSBs.…”

Lithium ion conductivity of complex hydrides incorporating multiple closo‑type complex anions

“…S6). These results would originate from the structural deviations such as the change in the lithium arrangements, which can lead to a higher carrier concentration in the former than in the latter [15] . Second, the ionic conductivity can increase by changes in the lattice size.…”

“…Closo -type complex hydrides, with ion conductivities approaching 10 −1 S cm −1 in their high-T phases, have also been intensively investigated [12][13][14][15] . Unlike LiBH 4 -based compounds, the complex anions in closo -type complex hydrides comprise not only multiple hydrogen atoms but also multiple boron (and carbon) atoms.…”