Extended Cycling Stability in an Anodeless Solid-State Battery at Ambient Pressure and Temperature Enabled by a Corroded, Reactive Interphase

Solid-state Li-ion batteries in the ‘anodeless’ configuration can lead to a significant increase in volumetric energy density compared to their liquid-electrolyte based counterparts. However, challenges related to the electrochemical stability of highly Li+ -conductive solid-state electrolytes need to be resolved to improve cyclability. Herein, we present a scalable, solution-phase interfacial engineering approach to generate a porous surface layer on the Cu current collector via a corrosion reaction involving the controlled hydrolysis of LiPF6 salt in EC-DEC at elevated temperatures. The optimal corrosion protocol results in a uniform reaction depth on the Cu foil with a reaction layer comprising of fluorides and oxides of Cu and Li. Subsequently, through a series of conversion reactions in a Li metal half-cell with Li1.3Al0.3Ti1.7(PO4)3 (LATP) as the solid-electrolyte, these F- and O-species on the porous interphase layer generated from Cu corrosion converted to lithium fluoride and lithium oxide, respectively, with the concomitant reduction of Cu(II) to its metallic form throughout the thickness of the interface layer. The reactive interphases are characterized with SEM, EDX, XPS and atom probe tomography along with electrochemical measure- ments to understand the composition, distribution, evolution and charge transfer properties during cycling. The unique interfacial microstructure consisting of a dense, well-adhered passivation layer resulted in a significantly improved coulombic efficiency of Li plating/stripping beyond 90% in an anodeless solid- state cell at ambient pressure and temperature.