Discharge products on metal/O2 cathodes mapped by X-ray transmission microscopy at the O-K edge

OLIVARES-MARÍN, MARA; ANDREA SORRENTINO; EVA PEREIRO; TEOFILO ROJO; TONTI, DINO; ALVARO Y. TESIO; RUNG-CHUAN LEE; NAE-LIH WU; IMANOL LANDA-MEDRANO; LORENZO STEVIANO; IDOIA RUIZ DE LARRAMENDI

Madrid

Congreso; VIII AUSE CONGRESS AND III ALBA USER'S MEETING; 2017

Asociación de Usuarios de Sincrotrón de España

The search for the next-generation batteries has recently focused on rechargeableaprotic metal-oxygen batteries, considered very attractive as room-temperature devices withhigh theoretical energy densities (5x compared to Li-ion) for application in electrical vehicles.Na and Li/O2 batteries form solid peroxides and superoxides during the discharging process,which then ?ideally- decompose into the metal ions and oxygen when charging. In practice, thedischarged compounds partially react with the electrolyte forming solid products that aredifficult to remove and hinder its decomposition. As a consequence, the electrode remainspassivated and the battery capacity fades within a few cycles. The composition and distributionof the compounds on the electrode is a critical information to understand the discharge processand mitigate its irreversible behavior.With this goal we used energy-dependent transmission soft X-ray microscopy (TXM),providing pixel-by-pixel absorption spectra with high spatial and energy resolution. Byscanning energy at the oxygen K edge it is possible to discriminate and quantify differentoxygen-containing chemical species, regardless of their crystalline state.1With Li/O2 we unambiguously demonstrated the presence of significant amounts ofsuperoxide forming a composite with peroxide,2 and secondary products such as carbonates orhydroxide using ether- or ionic liquid-based electrolytes,3 respectively. Conversely, in the caseof Na/O2 cells we detected significant peroxide amounts accompanying the superoxide mainproduct.4 The use of ether based electrolytes produces in both cells a carbonate-rich shellwrapping the discharged peroxide/superoxide composites.Acknowledgements. The X-ray microscopy experiments were performed at MISTRALbeamline at ALBA Synchrotron with the collaboration of ALBA staff. Work funded by theSpanish Government, the Generalitat de Catalunya, Eusko Jaurlaritza/Gobierno Vasco,Universidad del País Vasco, and FEDER fund.1 D. Tonti, M. Olivares-Marín, A. Sorrentino, and E. Pereiro, Studies of Lithium-Oxygen Battery Electrodes byEnergy- Dependent Full-Field Transmission Soft X-Ray Microscopy, in ?X-ray Characterization of NanostructuredEnergy Materials by Synchrotron Radiation?, M. Khodaei and L. Petaccia (Eds.), InTech, 2017.2 M. Olivares-Marín, A. Sorrentino, R. C. Lee, E. Pereiro, N. L. Wu, and D. Tonti, Nano Lett. 15, 6932, 20153 M. Olivares-Marín, A. Sorrentino, E. Pereiro, and D. Tonti, J. Power Sources, accepted4 I. Landa-Medrano, A. Sorrentino, L. Stievano, I. Ruiz de Larramendi, E. Pereiro, L. Lezama, T. Rojo and D. TontiNano Energy 37, 224, 2017