Enhanced high energy density hybrid lithium ion capacitor by garnet ceramic electrolyte for lithium anode protection

Abstract In this study, we report the fabrication of garnet-structure composited solid-state electrolyte with high compactness as a water-proof interlayer for multilayer water-proof protected-lithium-anode. It is revealed that with the addition of Li3BO3 into the sintering precursor, the cubic phase garnet Li6.75La3Zr1.75Nb0.25O12 with high lithium ion conductivity and compactness can be achieved at a low temperature of 1000 °C with a “binder-like” Li3BO3 glassy molten phase in the grain boundary, indicating Li3BO3 plays an important role on the densification of grain boundary and the improvement of the relative density. 50 mol % Li6.75La3Zr1.75Nb0.25O12–Li3BO3 pellet shows a high lithium ion conductivity of 2.08  ×  10−4 S cm−1 and a good chemical stability in 21 m LiTFSI “water-in-salt” electrolyte at 25 °C. Hybrid lithium ion capacitor using this garnet-ceramic electrolyte as interlayer for water-proof protected-lithium-anode, 21 m LiTFSI electrolyte and commercial activated carbon as the cathode shows a high working voltage of 4.0 V and a high energy density of 228.9 Wh (kg-carbon)−1 at a power density of 1343.2 W (kg-carbon)−1.