Soggy-sand electrolytes (solid–liquid composites, typically gel electrolytes, with synergistic electrical properties) are reviewed as far as status and perspectives are concerned. Major emphasis is put on the understanding of the local mechanism as well as the long-range transport along the filler network. The beneficial property spectrum includes enhanced conductivity of one ion type and decreased conductivity of the counter ion, but also the exciting mechanical properties of the solid–liquid composites. Inherent but not insurmountable problems lie in the reproducibility and stationarity of the composites microstructure and morphology. Owing to the huge parameter complexity and hence to the multitude of adjusting screws, there are various strategies for materials optimization. The technological relevance is enormous, in particular for battery electrolytes as here all the above-mentioned electrical and mechanical benefits are welcome. The soggy-sand electrolytes combine high Li⁺ conductivity, low anion conductivity and good wettability of electrode particles with the mechanical stability of semi-solids.

Rechargeable metal batteries are one of the most investigated electrochemical energy storage system at academic and industrial level because of their possibility to store higher energy compared to their counterparts employing carbon as an anode material. However, to produce reliable and durable metal batteries, it is of paramount importance to understand and circumvent (or ultimately overcome) the issues associated with the chemically reactive, ionically blocking and mechanically unstable interfaces and interphases of the metal electrode. Here, recent progress and the future perspective of this field are discussed from a physicochemical perspective while, at the same time, fundamentally relevant questions are raised. Metal electrode interfaces and interphases are critical for the development of future high-energy metal batteries. Here, Dr Jelena Popovic-Neuber discusses the state of the art, issues and strategies to improve the stability of metal electrodes toward practical battery systems.