Hydroxylated closo-Dodecaborates M2B12(OH)12(M = Li, Na, K, and Cs); Structural Analysis, Thermal Properties, and Solid-State Ionic Conductivity

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  • Mathias Jørgensen, Curtin University of Technology
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  • Steffen R.H. Jensen, Curtin University of Technology
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  • Terry D. Humphries, Curtin University of Technology
  • ,
  • Matthew R. Rowles, Curtin University of Technology
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  • Maria V. Sofianos, University College Dublin
  • ,
  • Craig E. Buckley, Curtin University of Technology
  • ,
  • Torben R. Jensen
  • Mark Paskevicius, Curtin University of Technology

Closo-borates and derivatives thereof have shown great potential as electrolyte materials for all-solid-state batteries owing to their exceptional ionic conductivity and high thermal and chemical stability. However, because of the myriad of possible chemical modifications of the large, complex anion, only a fraction of closo-borate derivatives has so far been investigated as electrolyte materials. Here, the crystal structures, thermal properties, and ionic conductivities of M2B12(OH)12 (M = Li, Na, K, and Cs) are investigated with a focus on their possible utilization as new solid-state ion conductors for solid-state batteries. The compounds generally show rich thermal polymorphism, with eight identified polymorphs among the four dehydrated compounds. Both Li2B12(OH)12 and Na2B12(OH)12 undergo a first-order transition, in which the cation sublattices become disordered, resulting in an order of magnitude jump in ionic conductivity for Na2B12(OH)12. K2B12(OH)12 undergoes a second-order polymorphic transition driven by a change in the anion-cation interaction, with no evidence of dynamic disorder. The ionic conductivities of M2B12(OH)12 range from 1.60 × 10-8 to 5.97 × 10-5 S cm-1 at 250 °C for M = Cs and Li, respectively, showing decreasing conductivity with increasing cation size. Compared with the analogous M2B12H12 compounds, such relatively low conductivities are suggested to be a consequence of strong and directional anion-cation interactions, resulting in a more static anion framework.

TidsskriftJournal of Physical Chemistry C
Sider (fra-til)11340-11349
Antal sider10
StatusUdgivet - 2020

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