Insights into the nature and evolution upon electrochemical cycling of planar defects in the β-NaMnO2 Na-ion battery cathode: An NMR and first-principles density functional theory approach

Raphaële J. Clément, Derek S. Middlemiss, Ieuan D. Seymour, Andrew J. Ilott, Clare P. Grey*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

53 Citations (Scopus)


β-NaMnO2 is a high-capacity Na-ion battery cathode, delivering ca. 190 mAh/g of reversible capacity when cycled at a rate of C/20. Yet, only 70% of the initial reversible capacity is retained after 100 cycles. We carry out a combined solid-state 23Na NMR and first-principles DFT study of the evolution of the structure of β-NaMnO2 upon electrochemical cycling. The as-synthesized structure contains planar defects identified as twin planes between nanodomains of the α and β forms of NaMnO2. GGA+U calculations reveal that the formation energies of the two polymorphs are within 5 meV per formula unit, and a phase mixture is likely in any NaMnO2 sample at room temperature. 23Na NMR indicates that 65.5% of Na is in β-NaMnO2 domains, 2.5% is in α-NaMnO2 domains, and 32% is close to a twin boundary in the as-synthesized material. A two-phase reaction at the beginning of charge and at the end of discharge is observed by NMR, consistent with the constant voltage plateau at 2.6-2.7 V in the electrochemical profile. GGA+U computations of Na deintercalation potentials reveal that Na extraction occurs first in α-like domains, then in β-like domains, and finally close to twin boundaries. 23Na NMR indicates that the proportion of Na in α-NaMnO2-type sites increases to 11% after five cycles, suggesting that structural rearrangements occur, leading to twin boundaries separating larger α-NaMnO2 domains from the major β-NaMnO2 phase.

Original languageEnglish
Pages (from-to)8228-8239
Number of pages12
JournalChemistry of Materials
Issue number22
Early online date1 Nov 2016
Publication statusPublished - 22 Nov 2016

Bibliographical note

Publisher Copyright:
© 2016 American Chemical Society.

This work was partially supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, under the Batteries for Advanced Transportation Technologies (BATT) Program subcontract no. 7057154 (R.J.C). C.P.G. and R.J.C. thank the EU ERC for an Advanced Fellowship for C.P.G. Via our membership in the UK's HEC Materials Chemistry Consortium, funded by EPSRC (EP/L000202), the first-principles calculations presented in this work used the ARCHER UK National Supercomputing Service ( Calculations were also carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. Rob Armstrong, Peter Bruce, and Juliette Billaud are thanked for helpful discussions and for providing the samples studied by NMR. Richard Harrison is thanked for help with the implementation of the Monte Carlo code in Python. Kellie Aldi and Jordi Cabana are acknowledged for their participationin a preliminary study on NaMnO2. Hajime Shinohara and Sian Dutton are thanked for their help with the experimental susceptibility measurements. Rebecca Dally and Steven Wilson are thanked for providing the samples for the high-temperature experimental magnetic susceptibility measurements.


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