Unlocking solid-state conversion batteries reinforced by hierarchical microsphere stacked polymer electrolyte

Pursuing all-solid-state lithium metal batteries with dual upgrading of safety and energy density is of great significance. However, searching compatible solid electrolyte and reversible conversion cathode is still a big challenge. The phase transformation at cathode and Li deformation at anode would usually deactivate the electrode?electrolyte interfaces. Herein, we propose an all-solid-state Li-FeF3 conversion battery reinforced by hierarchical microsphere stacked polymer electrolyte for the first time. This gC3N4 stuffed polyethylene oxide (PEO)-based electrolyte is lightweight due to the absence of metal element doping, and it enables the spatial confinement and dissolution suppression of conversion products at soft cathode-polymer interface, as well as Li dendrite inhibition at filler-reinforced anode-polymer interface. Two-dimensional (2D)-nanosheet-built porous g-C3N4 as three-dimensional (3D) textured filler can strongly cross-link with PEO matrix and LiTFSI (TFSI: bistrifluoromethanesulfonimide) anion, leading to a more conductive and salt-dissociated interface and therefore improved conductivity (2.5 x 10?4 S/cm at 60 ?C) and Li+ transference number (0.69). The compact stacking of highly regular robust microspheres in polymer electrolyte enables a successful stabilization and smoothening of Li metal with ultra-long plating/striping cycling for at least 10,000 h. The corresponding Li/LiFePO4 solid cells can endure an extremely high rate of 12 C. All-solid-state Li/FeF3 cells show highly stabilized capacity as high as 300 mAh/g even after 200 cycles and of -200 mAh/g at extremely high rate of 5 C, as well as ultra-long cycling for at least 1200 cycles at 1 C. High pseudocapacitance contribution (>55%) and diffusion coefficient (as high as 10?12 cm2/s) are responsible for this high-rate fluoride conversion. This result provides a promising solution to conversion-type Li metal batteries of high energy and safety beyond Li-S batteries, which are difficult to realize true ?all-solid-state? due to the indispensable step of polysulfide solid?liquid conversion. ? 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

Automated summary

The study introduces an all-solid-state Li-FeF3 conversion battery reinforced by hierarchical microsphere stacked polymer electrolyte for the first time. The utilization of a lightweight gC3N4 stuffed polyethylene oxide-based electrolyte enables improved conductivity and Li+ transference number, as well as enhanced stability and cycling performance of the battery. The results provide a promising solution for high energy and safe conversion-type Li metal batteries.