Perspective on recent improvements in experiment and theory towards realizing lithium metal electrodes with liquid electrolytes.

The lubricating properties of an ionic liquid on gold surfaces can be controlled through application of an electric potential to the sliding contact. A nanotribology approach has been used to study the frictional behavior of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py1,4]FAP) confined between silica colloid probes or sharp silica tips and a Au(111) substrate using atomic force microscopy. Friction forces vary with potential because the composition of a confined ion layer between the two surfaces changes from cation-enriched (at negative potentials) to anion-enriched (at positive potentials). This offers a new approach to tuning frictional forces reversibly at the molecular level without changing the substrates, employing a self-replenishing boundary lubricant of low vapor pressure.

Direct integration of a metallic lithium anode with the ceramic Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) electrolyte into an all-solid-state battery is highly challenging due to their chemical and electrochemical incompatibility. Herein, a layered hybrid solid electrolyte is designed by coating the ceramic LATP electrolyte with a protective polymer electrolyte, polyphosphazene/PVDF-HFP/LiBOB. This polymer electrolyte comprises highly Li⁺ conductive polyphosphazene and mechanically stable PVDF-HFP as the polymer matrix, and the mobile lithium ions in the polymer layer are supplied by LiBOB. Equipped with both polymer and ceramic components, the hybrid electrolyte possesses favorable features, such as a flexible surface, high ionic conductivity, high chemical stability against lithium and wide electrochemical stability window (4.7 V), which all to help realize its application in all-solid-state lithium batteries. The prepared all-solid-state battery with a metallic lithium anode and high-voltage Li₃V₂(PO₄)₃/CNT cathode shows high capacity and excellent cycling performance with negligible capacity loss over 500 cycles at 50 °C. Furthermore, the analysis of the hybrid solid electrolyte after long-term cycling demonstrates outstanding electrode/electrolyte interfacial stability. This study suggests that use of solid organic–inorganic hybrid electrolyte is a promising approach to circumvent the mechanical, chemical and electrochemical limitations at the interface of electrodes and ceramic electrolyte for all-solid-state batteries.