We recently reported an ultrafast high temperature sintering (UHS) for solid state electrolytes (Science, 2020, May Cover). The long sintering time of conventional syntheses can lead to Li loss in garnet SSEs caused by the evaporation of Li and the formation of secondary phases that lead to lower ionic conductivity. In contrast, the UHS technique enables us to tune the sintering time in units of seconds, which provides excellent control in terms of the Li content and grain growth. I will discuss our progress on applying UHS method to sintering various solid-state electrolyte, from compositions to microstructures. By programming the temperature and time (T-t), we can establish process diagrams to sinter porous vs. dense structures. The rapid sintering also allows us to sintering multilayer solid-state electrolytes with significantly reduced interlayer diffusion. In a separated topic, I will discuss a general design strategy for achieving one-dimensional (1D), high-performance polymer solid-state ion conductors through molecular channel engineering, which we demonstrate via Cu2+-coordination of cellulose nanofibrils. The cellulose nanofibrils by themselves are not ionic conductive; however, by opening the molecular channels between the cellulose chains through Cu2+ coordination we are able to achieve a Li-ion conductivity. This improved conductivity is enabled by a unique Li+ hopping mechanism that is decoupled from the polymer segmental motion. Also benefitted from such decoupling, the cellulose-based ion conductor demonstrates multiple advantages, including a high transference number (0.78 vs. 0.2–0.5 in other polymers2), low activation energy (0.19 eV), and a wide electrochemical stability window (4.5 V) that accommodate both Li metal anode and high-voltage cathodes. Furthermore, we demonstrate this 1D ion conductor not only as a thin, high-conductivity solid-state electrolyte but also as an effective ion-conducting additive for the solid cathode, providing continuous ion transport pathways with a low percolation threshold, which allowed us to utilize the thickest LiFePO4 solid-state cathode ever reported for high energy density (Nature, Oct 22).

High-performance solid-state electrolytes: Ultra-fast high temperature sintering (UHS) oxides and expanded cellulose

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