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Instruments / Technical Area	Publication Details	Published	Actions
B18-Core EXAFS I11-High Resolution Powder Diffraction	Deciphering the origin of the high capacities seen in magnesium borate polyanion cathodes Camilla Tacconis , Sunita Dey , Carson D. Mclaughlin , Debashis Tripathy , Heather F. Greer , Shaoliang Guan , Iuliia Mikulska , Israel Temprano , Clare P. Grey , Sian E. Dutton Journal Of Materials Chemistry A DOI: 10.1039/D5TA07239E Diamond Proposal Number(s): [33172, 14239] Open Access Show Abstract ▼ Abstract: Recent reviews have highlighted borate polyanion systems as promising high-voltage cathode candidates for rechargeable Mg-ion batteries (RMBs) [Coordination Chemistry Reviews, 427, 213551 (2021)]. However, evaluating the electrochemical performance of cathodes for Mg-ion batteries is challenging, with many reports relying on an observed electrochemical capacity rather than demonstrating Mg-ion (de)intercalation. To address these two points, we study three classes of borate polyanions: orthoborates M3(BO3)2, ludwigites M3BO5, and pyroborates M2B2O5 and use a suite of experimental techniques to investigate de-magnesiation on charging vs Li metal with a Li electrolyte. We select five representative materials Mg2Mn(BO3)2, Mg2Ni(BO3)2, Mg2FeBO5, MgFeB2O5 and MgFe0.5Mn0.5B2O5. Whilst promising first charge capacities up to 200 mAh g−1 are observed for ball-milled cathodes cycled at 55°C in a Li containing electrolyte, extensive post-cycling analysis using ex-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Synchrotron Powder X-ray Diffraction (SXRD), combined with operando X-ray Absorption Spectroscopy (XAS) and operando Online Electrochemical Mass Spectrometry (OEMS), show that the capacities obtained are not associated with Mg2+ mobility in the cathodes, de-magnesiation or transition-metal redox. The observed capacity originates from a process enhanced by ball-milling, which is common to all borate polyanions investigated in this work. This process is in part attributed to the irreversible reaction of an amorphous surface layer on the polycrystalline particle, rich in carbonate and glassy borate phases. Here we present the first systematic study of the viability of transition-metal borate polyanions as intercalation cathode materials for RMBs and conclude that, despite the promising electrochemistry, these materials do not de-magnesiate under our tested conditions.	Sep 2025
B18-Core EXAFS I11-High Resolution Powder Diffraction	Role of Fe impurity reactions in the electrochemical properties of MgFeB2O5 Camilla Tacconis , Sunita Dey , Carson D. Mclaughlin , Moulay Tahar Sougrati , Christopher A. O’keefe , Iuliia Mikulska , Clare P. Grey , Sian E. Dutton Chemistry Of Materials DOI: 10.1021/acs.chemmater.4c02855 Diamond Proposal Number(s): [33172, 34243] Open Access Show Abstract ▼ Abstract: We investigate magnesium–iron pyroborate MgFeB2O5 as a potential cathode material for rechargeable magnesium-ion batteries. Synchrotron powder X-ray diffraction and Mössbauer spectroscopy confirm its successful synthesis and iron stabilization in the high-spin Fe(II) state. Initial electrochemical testing against a lithium metal anode yields a first charge capacity near the theoretical value (147.45 mAh·g–1), suggesting MgFeB2O5 as a promising cathode candidate. However, multimodal analyses, including scanning electron microscopy energy-dispersive X-ray (SEM-EDS) analysis, operando X-ray absorption near edge spectroscopy (XANES), and Mössbauer spectroscopy, reveal the absence of any Fe redox reactions. Instead, we propose that the source of the observed capacity involves the irreversible reaction of a small (4–7 wt%) Fe metal impurity. These findings highlight the need for diverse characterization techniques in evaluating the performance of new Mg cathode materials, since promising initial cycling may be caused by competing side reactions rather than Mg (de)intercalation.	Dec 2024

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