title: Composition and evolution of the solid-electrolyte interphase in Na2Ti3O7 electrodes for Na-ion batteries: XPS and Auger parameter analysis.
abstract: Na2Ti3O7 is considered a promising negative electrode for Na-ion batteries; however, poor capacity retention has been reported and the stability of the solid-electrolyte interphase (SEI) could be one of the main actors of this underperformance. The composition and evolution of the SEI in Na2Ti3O7 electrodes is hereby studied by means of X-ray photoelectron spectroscopy (XPS). To overcome typical XPS limitations in the photoelectron energy assignments, the analysis of the Auger parameter is here proposed for the first time in battery materials characterization. We have found that the electrode/electrolyte interface formed upon discharge, mostly composed by carbonates and semicarbonates (Na2CO3, NaCO3R), fluorides (NaF), chlorides (NaCl) and poly(ethylene oxide)s, is unstable upon electrochemical cycling. Additionally, solid state nuclear magnetic resonance (NMR) studies prove the reaction of the polyvinylidene difluoride (PVdF) binder with sodium. The powerful approach used in this work, namely Auger parameter study, enables us to correctly determine the composition of the electrode surface layer without any interference from surface charging or absolute binding energy calibration effects. As a result, the suitability for Na-ion batteries of binders and electrolytes widely used for Li-ion batteries is questioned here.
authors: †CIC Energigune, Parque Tecnológico de Álava, Albert Einstein 48, 01510 Miñano, Spain.
authors: Miguel A
authors: MA
authors: Muñoz-Márquez
authors: †CIC Energigune, Parque Tecnológico de Álava, Albert Einstein 48, 01510 Miñano, Spain.
authors: Maider
authors: M
authors: Zarrabeitia
authors: †CIC Energigune, Parque Tecnológico de Álava, Albert Einstein 48, 01510 Miñano, Spain.
authors: Elizabeth
authors: E
authors: Castillo-Martínez
authors: ‡Departamento de Química Inorgánica, Universidad del País Vasco UPV/EHU, 48080 Bilbao, Spain.
authors: Aitor
authors: A
authors: Eguía-Barrio
authors: †CIC Energigune, Parque Tecnológico de Álava, Albert Einstein 48, 01510 Miñano, Spain.|‡Departamento de Química Inorgánica, Universidad del País Vasco UPV/EHU, 48080 Bilbao, Spain.
authors: Teófilo
authors: T
authors: Rojo
authors: †CIC Energigune, Parque Tecnológico de Álava, Albert Einstein 48, 01510 Miñano, Spain.
authors: Montse
authors: M
authors: Casas-Cabanas
keywords: Auger parameter; Na-ion battery; Na2Ti3O7; XPS; solid-electrolyte interphase