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Summary Among the phenomena related to the surface rearrangement of cations in perovskite-based oxides, A-site cation enrichment, Sr in particular, near the surface has been frequently observed. Upon annealing in an oxidizing atmosphere, Sr is often enriched on the surface as compared with the bulk composition of the material, which eventually forms Sr-rich phases or rearranges the crystal structure of the surface. This Sr segregation changes the structure and composition of the perovskite surfaces and thus affects the stability of the materials and the reactivity with gas phases. In this regard, many studies have been carried out in the field of solid oxide electrochemical cells (SOCs). In this review, we summarize the latest research efforts on Sr segregation in perovskite-based SOC O2 electrodes, with a focus on how excess Sr is present. We then discuss the origins of Sr segregation and suggest strategies for suppressing it to realize high-performance perovskite-based O2 electrodes.

Thin-film solid oxide fuel cells (TF-SOFCs) using a dense and thin electrolyte have attracted much attention as a promising portable power generator because they can lower the operating temperature of devices, which is a key issue related to conventional SOFCs, to below 500 °C and are compatible with several microfabrication processes. Highly porous interconnected Pt thin films are now widely used as oxygen electrodes, but their poor thermal stability seriously hampers the sustainable operation of TF-SOFCs. Here, we demonstrate how Al2O3 layers coated through atomic layer deposition effectively suppress the degradation of nanoporous Pt thin-film electrodes. Although Al2O3 is an electrical insulator, the selection of an appropriate overcoat thickness ensures stable electrochemical reaction sites of the Pt electrode at high temperatures even without serious current collection or gas flow issues. As a result, a 3.6-nm-thick Al2O3 layer maintains the high specific surface area morphology of Pt thin films at 450 °C and improves the electrode activity by more than twofold compared to an uncoated sample. These results suggest that a simple and scalable coating strategy enables the implementation of TF-SOFCs with ideal performance and durability outcomes.

The organophosphorus compounds tris(trimethylsilyl) phosphite (TMSP) and vinylene carbonate (VC) have been considered for use as functional additives to improve the electrochemical performance of Li 1.1 Mn 1.86 Mg 0.04 O 4 (LMO)/graphite full cells. Our investigation reveals that the combination of VC and TMSP as additives enhances the cycling properties and storage performance of full cells at 60 °C. The unique functions of the TMSP additive in the VC electrolyte are investigated via ex situ X-ray photoelectron spectroscopy (XPS) and 19 F nuclear magnetic resonance (NMR) measurements. The TMSP additive effectively eliminates trace water and hydrogen fluoride (HF) and produces a protective film on the LMO cathode that alleviates manganese dissolution at 60 °C.

Tris(pentafluorophenyl) borane (TPFPB) is evaluated as an additive for improving electrochemical performance of lithium peroxide (Li 2 O 2 )-based electrodes. It is found that TPFPB significantly reduced the charge potential of Li 2 O 2 -based electrodes during the first charge process and improved reversible capacity during cycling without adding air (or O 2 ) to the cell. To confirm the effect of TPFPB on electrolyte decomposition, the surface chemistry of Li 2 O 2 -based electrodes cycled in electrolytes with and without TPFPB was investigated.

A novel dimeric ionic liquid based on imidazolium cation and bis(trifluoromethanesulfonyl) imide (TFSI) anion has been synthesized through a metathesis reaction. Its chemical shift values and thermal properties are identified via 1 H nuclear magnetic resonance (NMR) imaging and differential scanning calorimetry (DSC). The effect of the synthesized dimeric ionic liquid on the interfacial resistance of gel polymer electrolytes is described. Differences in the SEM images of lithium electrodes after lithium deposition with and without the 1,1′-pentyl-bis(2,3-dimethylimidazolium) bis(trifluoromethane-sulfonyl)imide (PDMITFSI) ionic liquid in gel polymer electrolytes are clearly discernible. This occurs because the PDMITFSI ionic liquid with hydrophobic moieties and polar groups modulates lithium deposit pathways onto the lithium metal anode. Moreover, high anodic stability for a gel polymer electrolyte with the PDMITFSI ionic liquid was clearly observed.