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O3 to O1 Phase Transitions in Highly Delithiated NMC811 at Elevated Temperatures.

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Coates, Chloe S 
Märker, Katharina 
Mahadevegowda, Amoghavarsha 


Nickel-rich layered oxide cathodes such as NMC811 (LixNi0.8Mn0.1Co0.1O2) currently have the highest practical capacities of cathodes used commercially, approaching 200 mAh/g. Lithium is removed from NMC811 via a solid-solution behavior when delithiated to xLi > 0.10, maintaining the same layered (O3 structure) throughout as observed via operando diffraction measurements. Although it is possible to further delithiate NMC811, it is kinetically challenging, and there are significant side reactions between the electrolyte and cathode surface. Here, small format, NMC811-graphite pouch cells were charged to high voltages at elevated temperatures and held for days to access high states of delithiation. Rietveld refinements on high-resolution diffraction data and indexing of selected area electron diffraction patterns, both acquired ex situ, show that NMC811 undergoes a partial and reversible transition from the O3 to the O1 phase under these conditions. The O1 phase fraction depends not only on the concentration of intercalated lithium but also on the hold temperature and hold time, indicating that the phase transition is kinetically controlled. 1H NMR spectroscopy shows that the proton concentration decreases with O1 phase fraction and is not, therefore, likely to be driving the O3-O1 phase transition.



40 Engineering, 4016 Materials Engineering, 34 Chemical Sciences, 3406 Physical Chemistry

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Chem Mater

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American Chemical Society (ACS)
Faraday Institution (FIRG024)
Faraday Institution (Unknown)
Engineering and Physical Sciences Research Council (EP/P030467/1)
This work was supported by the Faraday Institution Degradation Project (grant nos. FIRG001 and FIRG024). PXRD measurements were carried out at the I11 beamline at Diamond Light Source, for which the authors acknowledge the award of a Block Allocation Grant (CY28349). The authors would like to acknowledge the EPSRC Underpinning Multi-User Equipment Call (EP/P030467/1) for funding the Thermo Scientific (FEI) Talos F200X G2. The authors thank Dr Nigel Howard for performing the ICP measurements and Dr Joshua Bocarsly for helping to coordinate and perform some of the PXRD measurements at I11.