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Instruments / Technical Area	Publication Details	Published	Actions
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 LiNi 0.8 Co 0.2−y Al y O 2 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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