Polymer electrolytes reinforced by 2D fluorinated filler for all-solid-state Li-Fe-F conversion-type lithium metal batteries

The polyethylene oxide (PEO) based solid-state batteries are considered as promising candidates for the next-generation Li metal batteries with high energy density and safety. However, the low Li-ion conductivity and high-voltage endurability hinder the further applications of PEO-based electrolytes. To overcome these issues, herein two-dimensional (2D) CeF3 nanoplates with maximally exposed [001] crystal faces are introduced into the PEO matrix to expand the electrochemical window and improve Li-ion conduction and transport. The optimized crystal shape and crystal face anisotropy of CeF3 nanoplate filler reduce the crystallinity of composite solid polymer electrolyte (CSPE) via its Lewis acid-base interaction with ether oxygen of PEO. The Li-affinity [100] and Li-repellent [001] crystal faces of CeF3 nanoplates synergistically realize the dissociation of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), fast Li-adsorption/desorption, and Li+ migration. The optimized CSPE-0.1CeF3 membrane enables the achievement of Li metal batteries with high endurability and stability, from the kinetically favorable Li/Li symmetric cells with long-term cycling over 8000 h. The highly reversible Li/LiFePO4 cells exhibit a capacity retention of 109.2 mAh·g−1 after 1000 cycles at 1 C, corresponding to a low capacity fading rate of 0.026% per cycle. The conversion-type all-solid-state Li/CSPE-0.1CeF3/FeF3 cells show a high reversible capacity of 201.9 mAh·g−1 after long-term 600 cycles and of 231.1 mAh·g−1 at an ultra-high rate of 5 C.