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.