Impact of Structural Water on Ionic Conductivity in Hydridoborates Solid Electrolytes
Abstract
Sodium closo-hydridoborates have emerged as promising solid-state electrolytes for Na-ion batteries because of their high ionic conductivity and electrochemical stability. However, their sensitivity to water makes them challenging to scale-up. In this work, we systematically investigate the impact of controlled hydration on the structure, ion transport, and interfacial stability of an anion-mixed hydridoborate, Na4(B10H10)0.5(B12H12)0.5. By exposing the hydridoborate to varying degrees of relative humidity (RH) of 30-70%, we find that hydration at 30% enables retention of its moderate Na-ion conductivity (∼0.7 mS/cm) while higher hydration levels lead to the separation of the two anions ([B10H10] 2− and [B12H12] 2−), resulting in significant disruption in the Na ion conduction pathways. X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR) measurements indicate that hydration leads to the formation of distinct crystalline phases and alters the local ion coordination environments. The hydrated phase at 30% RH reversibly returns the original structure, restoring its ionic conductivity and compatibility with Na metal anodes. These findings provide insights into the role of structural water in Na-ion transport and a practical strategy for the use of moisturesensitive closo-hydridoborates solid state electrolytes.
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BibTeX
@misc{koh2026impact,
title = {{Impact of Structural Water on Ionic Conductivity in Hydridoborates Solid Electrolytes}},
author = {Hyeongjun Koh and Venkata Surya Chaitanya Kolluru and J. David Bazak and Yiteng Zheng and Tiffany L. Kinnibrugh and Bruce E. Koel and Timothy T. Fister and Maria K. Y. Chan and Kelsey B. Hatzell},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009670/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009670/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Impact of Structural Water on Ionic Conductivity in Hydridoborates Solid Electrolytes
AU - Hyeongjun Koh
AU - Venkata Surya Chaitanya Kolluru
AU - J. David Bazak
AU - Yiteng Zheng
AU - Tiffany L. Kinnibrugh
AU - Bruce E. Koel
AU - Timothy T. Fister
AU - Maria K. Y. Chan
AU - Kelsey B. Hatzell
PY - 2026
DA - 2026/09/29
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009670/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009670/v1
AB - Sodium closo-hydridoborates have emerged as promising solid-state electrolytes for Na-ion batteries because of their high ionic conductivity and electrochemical stability. However, their sensitivity to water makes them challenging to scale-up. In this work, we systematically investigate the impact of controlled hydration on the structure, ion transport, and interfacial stability of an anion-mixed hydridoborate, Na4(B10H10)0.5(B12H12)0.5. By exposing the hydridoborate to varying degrees of relative humidity (RH) of 30-70%, we find that hydration at 30% enables retention of its moderate Na-ion conductivity (∼0.7 mS/cm) while higher hydration levels lead to the separation of the two anions ([B10H10] 2− and [B12H12] 2−), resulting in significant disruption in the Na ion conduction pathways. X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR) measurements indicate that hydration leads to the formation of distinct crystalline phases and alters the local ion coordination environments. The hydrated phase at 30% RH reversibly returns the original structure, restoring its ionic conductivity and compatibility with Na metal anodes. These findings provide insights into the role of structural water in Na-ion transport and a practical strategy for the use of moisturesensitive closo-hydridoborates solid state electrolytes.
ER -