title: Mechanisms of Sodium Insertion/Extraction on the Surface of Defective Graphenes.
abstract: Two chemically synthesized defective graphene materials with distinctly contrasting extended structures and surface chemistry are used to prepare sodium-ion battery electrodes. The difference in electrode performance between the chemically prepared graphene materials is qualified based on correlations with intrinsic structural and chemical dissimilarities. The overall effects of the materials' physical and chemical discrepancies are quantified by measuring the electrode capacities after repeated charge/discharge cycles. Solvothermal synthesized graphene (STSG) electrodes produce capacities of 92 mAh/g in sodium-ion batteries after 50 cycles at 10 mA/g, while thermally exfoliated graphite oxide (TEGO) electrodes produce capacities of 248 mAh/g after 50 cycles at 100 mA/g. Solid-state23Na nuclear magnetic resonance spectroscopy is employed to locally probe distinct sodium environments on and between the surface of the graphene layers after charge/discharge cycles that are responsible for the variations in electrode capacities. Multiple distinct sodium environments of which at least 3 are mobile during the charge-discharge cycle are found in both cases, but the majority of Na is predominantly located in an immobile site, assigned to the solid electrolyte interface (SEI) layer. Mechanisms of sodium insertion and extraction on and between the defective graphene surfaces are proposed and discussed in relation to electrode performance. This work provides a direct account of the chemical and structural environments on the surface of graphene that govern the feasibility of graphene materials for use as sodium-ion battery electrodes.
authors.affiliation: School of Chemistry, UNSW Australia , Sydney NSW 2052, Australia.|Australia Nuclear Science and Technology Organisation , Kirrawee, DC NSW 2253, Australia.
authors.forename: James C
authors.initials: JC
authors.lastname: Pramudita
authors.affiliation: Mark Wainwright Analytical Centre, UNSW Australia , Sydney NSW 2052, Australia.
authors.forename: Aditya
authors.initials: A
authors.lastname: Rawal
authors.affiliation: School of Chemistry, University of Sydney , Sydney NSW 2006, Australia.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Choucair
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma , Parco Area delle Scienze 7/a, 43124, Parma, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Pontiroli
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma , Parco Area delle Scienze 7/a, 43124, Parma, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Magnani
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory , Chilton, Didcot, Oxfordshire OX11 0QX, U.K.
authors.forename: Mattia
authors.initials: M
authors.lastname: Gaboardi
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma , Parco Area delle Scienze 7/a, 43124, Parma, Italy.
authors.forename: Mauro
authors.identifier: http://orcid.org/0000-0002-6879-2687
authors.initials: M
authors.lastname: Riccò
authors.affiliation: School of Chemistry, UNSW Australia , Sydney NSW 2052, Australia.
authors.forename: Neeraj
authors.identifier: http://orcid.org/0000-0003-1197-6343
authors.initials: N
authors.lastname: Sharma
keywords: graphene; negative electrodes; sodium-ion batteries; solid-state NMR; solid−electrolyte interface layer