Surface Enhanced Raman Microscopy in the Study of Li-Ion and Li-Air Battery Interfaces

Surface layers on lithium battery electrodes play a vital role in affecting battery performance, ageing mechanics and safety. Particularly, the solid electrolyte interphase (SEI), which is a protecting layer formed on the negative electrode of lithium-ion batteries as a result of electrolyte decomposition, significantly impacts upon irreversible charge “loss”, rate capability, cyclability, exfoliation of graphite and safety.

The investigation of surface layer formation is also important in the understanding of the operation of the lithium-oxygen battery. The non-aqueous lithium-oxygen cell is one of a host of emerging opportunities available for enhanced energy storage [1]. Unlike a conventional battery where the reagents are contained within the cell, the lithium-oxygen cell uses dioxygen from the atmosphere to electrochemically form the discharge product lithium peroxide. Degrees of reversible oxidation and formation of lithium peroxide has been demonstrated in a number of non-aqueous electrolyte classes, mostly notably in dimethysulfoxide based electrolytes [2], thus making the lithium-oxygen cell a potential energy storage device.

The design and optimisation of techniques based on both surface-enhanced Raman spectroscopy (SERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) for ultra-sensitive analysis will be presented in the study the formation and composition of interfaces on lithium battery electrode materials. SHINERS, first reported by Prof. Tian and his co-workers [3] provides, as does SERS, an ultra-sensitive technique for understanding the formation and composition of interphases/ passivation layers on electrode materials and is considered to be a powerful technique for in situ surface analysis. The highest enhancement of Raman scattering using SHINERS appears at the junction between the particles and substrate as hot spots with magnitudes of up to 4x10⁸ fold. Raman signals can be greatly enhanced by surface plasmon resonance generated on the surface of gold or silver nanoparticles. In SHINERS, the gold nanoparticles are coated with ultrathin silica or alumina layer. The inert shell is expected to be thin, uniform, fully enclosed and optically transparent so that it can retain the surface enhancement and ensure that there is no direct contact between the probed substance and the gold core. The shell-isolated nanoparticles are then spread onto the electrode surface and assembled into an in situ Raman electrochemical cell.

The poster will present our groups recent results of the spectro-electrochemistry studies of dioxygen in non-aqueous electrolytes, as well the use of SHINERS to understand model electrode interfaces within Li-ion battery electrolytes.

References:

1. P.G. Bruce, S. Freunberger, L.J. Hardwick, J.-M. Tarascon, Nature Mater. (2012) 11 19

2. Z. Peng, S.A. Freunberger, Y. Chen, P.G. Bruce, Science, (2012) 337 563

3. Li et al. Nature (2010) 464 392