Phase-pure BBC-structured Na4(B10H10)(B12H12), a closo-borate-type electrolyte, has been synthesised for the first time. Its Na-ion conductivity shows complex pressure dependence, likely due to structural changes. Understanding the mechanism behind this observation would allow phase-engineering of the closo-borate electrolyte for optimized usage and provide a wider understanding of the relationship between hydroborate’s performance and pressure. In this context, we aim to perform operando XRD at BM01 to track structural changes with applied pressure up to 1000 MPa.