Understanding the fundamental reaction mechanisms in the lithium oxygen battery is a key step in the development of a stable electrolyte. Surface enhanced Raman spectroscopy (SERS) is a non-destructive and non-invasive technique; it can be used to investigate the chemical bonding of surface species, making it a very valuable technique to study in situ the oxygen reduction and evolution reactions taking place at the liquid-solid interface. However the Raman signal is inherently weak. The signal can be enhanced by roughening the cathode surface, using an electrochemical oxidation/reduction cycle (ORC)¹. By studying the oxidation reduction/evolution reaction within dimethyl sulfoxide based electrolytes on SERS active gold; the presence of both superoxide (O₂^-) and lithium peroxide (Li₂O₂) has been observed at the interface². SERS however is limited to precious metal surfaces.

 Unlike SERS the use of SHINERs (shell isolated nanoparticles for enhanced Raman spectroscopy³) (figure 1) is not restricted to precious metal surfaces.  Adding a near-monolayer of SHINERS can enhance the Raman signal by ca. 10⁸. The gold nanoparticle has a strong electromagnetic field which enhances the Raman signal, whilst the SiO₂ shell inhibits any catalytic effect from the gold core. SHINERs can therefore enhance a variety of surfaces, such as carbon, which have been previously very challenging to analyse.

   In situ studies with SHINERS without the presence of lithium have been able to track the reaction mechanism on planar, glassy carbon, gold, palladium and platinum surfaces, with the reduction and oxidation of free O₂^- observed. Further studies on glassy carbon in the presence of lithium have detected lithium superoxide (LiO₂) and lithium peroxide (Li₂O₂) species in MeCN and DMSO electrolyte media’s. We are continuing to further develop this technique within non-aqueous electrolytes on a wider range electrode surfaces.