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Bulk fatigue induced by surface reconstruction in layered Ni-rich cathodes for Li-ion batteries

DOI: 10.1038/s41563-020-0767-8 DOI Help

Authors: Chao Xu (University of Cambridge; The Faraday Institution) , Katharina Märker (University of Cambridge; The Faraday Institution) , Juhan Lee (The Faraday Institution; University of Liverpool) , Amoghavarsha Mahadevegowda (University of Cambridge; The Faraday Institution) , Philip J. Reeves (University of Cambridge; The Faraday Institution) , Sarah J. Day (Diamond Light Source) , Matthias F. Groh (University of Cambridge) , Steffen P. Emge (University of Cambridge) , Caterina Ducati (The Faraday Institution; University of Cambridge) , B. Layla Mehdi (The Faraday Institution; University of Liverpool) , Chiu C. Tang (Diamond Light Source) , Clare P. Grey (The Faraday Institution; University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature Materials , VOL 414

State: Published (Approved)
Published: August 2020
Diamond Proposal Number(s): 16733 , 25186

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.

Journal Keywords: Batteries; Solid-state chemistry

Subject Areas: Materials, Chemistry, Energy


Instruments: I11-High Resolution Powder Diffraction