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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Structural origins of voltage hysteresis in the Na-ion cathode P2–Na0.67[Mg0.28Mn0.72]O2: A combined spectroscopic and density functional theory study Euan N. Bassey , Philip J. Reeves , Michael A. Jones , Jeongjae Lee , Ieuan D. Seymour , Giannantonio Cibin , Clare P. Grey Chemistry Of Materials 68 DOI: 10.1021/acs.chemmater.1c00248 Diamond Proposal Number(s): [24303] Open Access Show Abstract ▼ Abstract: P2-layered sodium-ion battery (NIB) cathodes are a promising class of Na-ion electrode materials with high Na+ mobility and relatively high capacities. In this work, we report the structural changes that take place in P2–Na0.67[Mg0.28Mn0.72]O2. Using ex situ X-ray diffraction, Mn K-edge extended X-ray absorption fine structure, and 23Na NMR spectroscopy, we identify the bulk phase changes along the first electrochemical charge–discharge cycle—including the formation of a high-voltage “Z phase”, an intergrowth of the OP4 and O2 phases. Our ab initio transition state searches reveal that reversible Mg2+ migration in the Z phase is both kinetically and thermodynamically favorable at high voltages. We propose that Mg2+ migration is a significant contributor to the observed voltage hysteresis in Na0.67[Mg0.28Mn0.72]O2 and identify qualitative changes in the Na+ ion mobility.	Jun 2021
I11-High Resolution Powder Diffraction	Bulk fatigue induced by surface reconstruction in layered Ni-rich cathodes for Li-ion batteries Chao Xu , Katharina Märker , Juhan Lee , Amoghavarsha Mahadevegowda , Philip J. Reeves , Sarah J. Day , Matthias F. Groh , Steffen P. Emge , Caterina Ducati , B. Layla Mehdi , Chiu C. Tang , Clare P. Grey Nature Materials 414 DOI: 10.1038/s41563-020-0767-8 Diamond Proposal Number(s): [16733, 25186] Show Abstract ▼ Abstract: Ni-rich layered cathode materials are among the most promising candidates for high-energy-density Li-ion batteries, yet their degradation mechanisms are still poorly understood. We report a structure-driven degradation mechanism for NMC811 (LiNi0.8Mn0.1Co0.1O2), in which a proportion of the material exhibits a lowered accessible state of charge at the end of charging after repetitive cycling and becomes fatigued. Operando synchrotron long-duration X-ray diffraction enabled by a laser-thinned coin cell shows the emergence and growth in the concentration of this fatigued phase with cycle number. This degradation is structure driven and is not solely due to kinetic limitations or intergranular cracking: no bulk phase transformations, no increase in Li/Ni antisite mixing and no notable changes in the local structure or Li-ion mobility of the bulk are seen in aged NMCs. Instead, we propose that this degradation stems from the high interfacial lattice strain between the reconstructed surface and the bulk layered structure that develops when the latter is at states of charge above a distinct threshold of approximately 75%. This mechanism is expected to be universal in Ni-rich layered cathodes. Our findings provide fundamental insights into strategies to help mitigate this degradation process.	Aug 2020
I09-Surface and Interface Structural Analysis	Revisiting the charge compensation mechanisms in LiNi0.8Co0.2−yAlyO2 systems Zachary W. Lebens-Higgins , Nicholas V. Faenza , Maxwell D. Radin , Hao Liu , Shawn Sallis , Jatinkumar Rana , Julija Vinckeviciute , Philip J. Reeves , Mateusz Zuba , Fadwa Badway , Nathalie Pereira , Karena W. Chapman , Tien-Lin Lee , Tianpin Wu , Clare P. Grey , Brent Melot , Anton Van Der Ven , Glenn G. Amatucci , Wanli Yang , Louis F. J. Piper Materials Horizons 5 DOI: 10.1039/C9MH00765B Diamond Proposal Number(s): [19162] Open Access Show Abstract ▼ Abstract: Oxygen participation, arising from increased transition metal–oxygen covalency during delithiation, is considered essential for the description of charge compensation in conventional layered oxides. The advent of high-resolution mapping of the O K-edge resonant inelastic X-ray scattering (RIXS) provides an opportunity to revisit the onset and extent of oxygen participation. Combining RIXS with an array of structural and electronic probes for the family of Ni-rich LiNi0.8Co0.2−yAlyO2 cathodes, we identify common charge compensation regimes that are assigned to formal transition metal redox (<4.25 V) and oxygen participation through covalency (>4.25 V). From O K-edge RIXS maps, we find the emergence of a sharp RIXS feature in these systems when approaching full delithiation, which has previously been associated with lattice oxidized oxygen in alkali-rich systems. The lack of transition metal redox signatures and strong covalency at these high degrees of delithiation suggest this RIXS feature is similarly attributed to lattice oxygen charge compensation as in the alkali-rich systems. The RIXS feature's evolution with state of charge in conventional layered oxides is evidence that this feature reflects the depopulation of occupied O 2p states associated with oxygen participation.	Jul 2019

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