Review of local in situ probing techniques for the interfaces of lithium-ion and lithium-oxygen batteries

Electrodes in lithium-ion and post-lithium-ion batteries are made of composite materials exposing a variety of different surfaces towards the electrolyte. This causes a distribution of current densities and consequently locally different changes of interfaces and bulk materials that might be critical for the performance and durability of secondary batteries. The optimization of local structures of battery materials is hindered by a lack of local techniques that provide in situ reactivity information from such hidden interfaces. A variety of new electrochemical scanning probe techniques are currently adapted to the investigation of battery materials under near-realistic environmental conditions. The review provides a critical assessment of this development with a particular emphasis on the assessment of the passivating properties of solid–electrolyte interphases, the extension of the concepts to lithium–oxygen cells, and attempts to image ion intercalation reactions

In situ quantification of the swelling of graphite composite electrodes by scanning electrochemical microscopy

The physical swelling of uncharged graphite composite electrodes due to electrolyte-binder interactions is investigated by scanning electrochemical microscopy (SECM) using 2,5-di-tert-butyl-1,4,-dimethoxybenzene as a redox mediator. A series of approach curves at the same location is conducted in order to quantify in situ and locally the physical swelling. The film thickness change δfilm amounted to 9.1 μm on average for a 80 μm thick uncharged graphite composite electrode in LP40 electrolyte between 1.1 and 5.9 h. Curves of δfilm vs. t usually reach a saturation within 12 h. The swelling ratio χ varies from 0.3% to 17.6% for uncharged graphite composite electrodes from the same batch in the same electrolyte. In contrast, the 8 μm thick polyvinylidene fluoride (PVDF) model sample swelled by χ = 99%. Approach curves demonstrate that swelling of the PVDF is the main cause for the physical swelling of uncharged graphite composite electrodes. Both PVDF model sample and uncharged graphite composite electrodes show locally different swelling ratios by SECM imaging. Based on these results a swelling model is proposed, where the uncharged graphite composite electrode swells physically on average by at least χ = 11% and the local topography is changing during swelling

Electrochemical analysis of nanostructured iron oxides using cyclic voltammetry and scanning electrochemical microscopy

Iron oxides in general and especially hematite, ?-Fe2O3, have become promising materials for the alkaline water electrolysis and photoelectrochemical water splitting, respectively. In the present study electrocatalytic electrodes with a thin film of ?-Fe2O3 and with vertically aligned ?-Fe2O3 nanowires were prepared. Cyclic voltammograms of the ?-Fe2O3 nanowires revealed differences including a series of three unreported cathodic signals when compared to previously published voltammograms for polycrystalline iron oxides. The generation-collection mode of scanning electrochemical microscopy (SECM) using nanostructured Pt microdisc probes was exploited to detect soluble reaction products formed at the voltammetric peaks of the ?-Fe2O3 electrode. SECM tip-substrate voltammetry unexpectedly showed that the reduction of FeVI to FeIII on the cathodic sweep is accompanied by significant O2 evolution