current density of 1.2 mA cm −2 . Furthermore, the solid LiCoO 2 /Li cell with the modified garnet delivers a discharge capacity of 130 mAh g −1 at 30 °C, accompanied by a capacity retention of 81% after 150 cycles. This study proposes a promising solution for improvement of air stability and interfacial compatibility of garnet using facile molten salt treatment.

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Solid-state lithium batteries (SSLBs) are promising energy storage devices in the future due to their high theoretical energy density and enhanced safety. However, the practical energy density of SSLBs is severely constrained by the limited mass loading of cathode materials, which is related to sluggish charge transfer inside the thick cathodes. In this work, the solid-state batteries with high-mass-loading cathodes are realized by introduction of three-dimensional (3D) electronic-conductivity current collectors and in situ solidification of polymer electrolytes. The porous electronic current collectors of 3D carbon felts accommodate the flowing cathode slurry with considerably increased loading of cathode materials. Subsequently, the in situ solidified polymer electrolytes ensure conformal ionic conducting channels inside the cathodes, along with the formation of intimate and flexible contacts at cathode/electrolyte interfaces. In this way, the solid-state LiFePO4/garnet/Li batteries with cathode loading of 6.2 mg cm−2 show an initial discharge capacity of 159.4 mAh g−1 and a capacity retention of 92.1% after 100 cycles at 30 °C and 0.1 C. Furthermore, the cathode mass loading as high as 27.8 mg cm−2 is achieved with a corresponding areal capacity of approximately 4.2 mAh cm−2. This work proposes a promising unique cathode architecture for solid-state lithium batteries with high mass loading of the cathode.