A comprehensive understanding of how local surface (de)activation and site-specific differential reactivity impacts the dynamic ion-transfer capabilities of ion-battery electrode interfaces has yet to be fully elucidated. Exploring quantitatively local ionic reactivity is of paramount importance for the design of efficient storage materials. New in-situ analytical tools are required to address present and future battery challenges by incorporating versatile platforms capable of imaging surface redox reactivity and ionic transfer reactions for species such as Li+, Na+ and K+ at interfacial and bulk nanostructures in non-aqueous electrolytes. Here, we introduce an experimental approach for detecting redox reactivity and quantifying and imaging ionic reactivity on operating ion-battery electrodes using scanning electrochemical microscopy (SECM). The measurement principle is based on SECM probes that integrate mercury mirco- and nano- cap electrodes on which alkaline ions can be detected by means of fast-scan anodic stripping voltammetry (Figure 1A and B). In a first application, these probes were used for the detection of Na+, Li+ and K+ in propylene carbonate, as well as the deposition of Li+ on operating Au electrodes. The probe potential provided chemical specificity while the probe limiting current permitted to measure ionic fluxes with excellent stability and linearity for concentrations in the molar to sub-millimolar range. We also demonstrated the possibility of carrying out analysis on electrodes of ~100 nm. In following studies, we demonstrated the utility of our approach for elucidating ion insertion in ~10-layer graphene as well as the role of surface patterns as points of entry for ions into its bulk structure. Stripping-based measurements provided an increase sensitivitiy to small differences in local ion flux. Further studies used simultaneous ionic and redox probing of redox active polymer interfaces to understand the effects of charge trapping and specific interactions between the electrolyte composition and charge accessibility. The described SECM technique represents an unprecedented step in the analysis of ion insertion mechanisms into highly localized electrode structures and ultra-thin samples. SECM mapping reveals aspects of surface reactivity that are lost during averaging in conventional battery testing.

Versatile in situ chemical imaging of alkali ion reactivity at battery interfaces

253rd National Meeting (2017)

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