Yttrium trifluoride doped polyacrylonitrile based carbon nanofibers as separator coating layer for high performance lithium-metal batteries

In this study, the yttrium trifluoride-doped polyacrylonitrile(PAN) based carbon nanofibers (YF3-PAN-CNFs) are successfully designed and prepared through the electro-blow spinning and carbonization strategies. And the YF3-PAN-CNFs acted as main materials of functional layer for modifying separator of lithium metal batteries are systematically studied and analyzed. The prepared CNFs have long-range ordered structures and high conductivity, which can extremely improve the transport of lithium ions and electrons during charge-discharge processes. The lithiophilic YF3 nanoparticles formed in the carbonization process can endow enough active sites to produce alloying reaction with Li, which makes the plating/stripping of Li more uniform. For the assembled Li||lithium iron phosphate (LiFePO4) battery, it still maintains a high specific discharge capacity of 137.1 mAh g-1 after 500 cycles at 0.5 C, which there is almost no specific discharge capacity degradation after long cycle. The modified separator for the Li||Li symmetric battery can effectively suppress the growth of lithium dendrites and improve cycle stability. Meanwhile, based on the strong chemical bonding between YF3 and lithium polysulfide combining the effectively physical confinement of the YF3-PAN-CNFs coating layer, the "shuttle effect" of lithium polysulfide also can be greatly suppressed. Thus the assembled Li||S battery using the separator has excellent electrochemical performance. Therefore, the YF3-PAN-CNFs modified separator will have a promising application prospect in lithium metal batteries even other high performance secondary batteries.