Performance of a 5 V-Class Thin-Film Li Battery at a High Current Density of ∼30 mA cm-2

All-solid-state Li batteries operating at high current densities exceeding 10 mA cm-2 are desired for high-power and rapid-charging batteries. Therefore, battery development needs to focus on reducing the electrolyte-electrode interface resistance at high current density, which is a major contributor to internal resistance. However, methods for reducing the electrolyte-electrode interfacial resistance at high current densities remain unexplored. Here, we demonstrate charge-discharge operation at 30 mA cm-2 using Li3PS4, LiNi0.5Mn1.5O4, and Li metal as a solid electrolyte, 5 V-class positive electrode, and negative electrode, respectively. The introduction of Li3PO4 buffer layers at both Li-Li3PS4 and Li3PS4-LiNi0.5Mn1.5O4 interfaces reduced the interfacial resistance 45,000-fold. Furthermore, the introduction of a 5 nm-thick Pt layer instead of Li3PO4 at the Li-Li3PS4 interface enabled charge-discharge operation under high-current-density conditions. This quantitative study highlights the importance of designing electrochemically robust negative electrode and electrolyte interfaces for high-power 5 V-class all-solid-state Li batteries.