Application Of Yttrium Fluoride Doped Carbon Fiber In Lithium Metal Batterie

Lithium metal batteries include lithium-ion batteries（Li-ion）,lithium-sulfur batteries（Li-S）and other high-energy-density batteries that use lithium metal as the anode.It relys on ultra-high theoretical capacity(～3860 m Ah g^-1)and low redox potential（-3.04 V vs.）has become a research hotspot in the field of electrochemical energy storage.However,the inherent lithium dendritic problem of lithium metal batteries hinders its development,and Li-S batteries also face the"shuttle effect"of lithium polysulfides.As a key component of the battery,the separator has become an effective entry point to solve the above-mentioned problems.The 3D network structure of carbon nanofibers has high porosity,which can improve the lyophilicity and lithium loading capacity of the separator.The alloying reaction between the metal fluoride and the lithium anode can induce the uniform deposition of lithium dendrites.In Li-S batteries,metal fluorides exhibit a strong anchoring effect on polysulfides.Therefore,in this paper,polyacrylonitrile（PAN）was used as the carbon source,based on electrostatic blowing technology and pre-oxidation carbonization strategy,combined with simple soaking method to grow metal fluoride（YF₃）,successfully prepared yttrium fluoride-doped carbon fiber（YF₃-PAN-CNFs）,and further developed and designed yttrium fluoride-doped porous carbon fibers（YF₃-PAN/PSF-CNFs）on this basis.（1）The PAN nanofibers prepared by electro-blow spinning technology were immersed in a PTFE/Y（NO₃）₃·6H₂O mixed solution to grow YF₃,combined with pre-oxidation and carbonization to obtain YF₃-PAN-CNFs-1.In order to prevent the irreversible spontaneous agglomeration of YF₃ particles,PAN/Y（NO₃）₃·6H₂O composite nanofibers were prepared,then soaked in PTFE solution and pre-oxidized and carbonized to obtain YF₃-PAN-CNFs-2.The high ionic strength of the YF₃ bond increased the band gap,making it incapable of electrochemical activity.Due to the high content of YF₃ in YF₃-PAN-CNFs-1,the conductivity of the material is deteriorated;while the sample of YF₃-PAN-CNFs-2 had less crystals,more defects,and abundant active sites,and the conductivity increases accordingly.The Li-LFP battery assembled on the basis of YF₃-PAN-CNFs-2 separator had almost no capacity decay after 500cycles,which showed that a proper amount of YF₃ doping is beneficial to improve the cycle stability.（2）Using PAN/PSF spinning solution to prepare two-component nanofibers,the subsequent soaking and carbonization process remained unchanged,and YF₃-PAN/PSF-CNFs were developed.Due to the strong jet drafting force caused by the conductive PSF during spinning,the diameter of the nanofibers was significantly reduced.In addition,PSF decomposed after carbonization to form a micro-mesoporous structure,which was beneficial to the rapid migration of ions in Li-ion batteries;application in Li-S batteries improved the ability to capture polysulfides.Results showed that the separator had a finer fiber diameter（145 nm）and a wider electrochemical stability window（4.9 V）.The Li-LFP battery assembled based on the diaphragm still maintained a high reversible capacity of 154.9 m Ah g^-1 even after 650cycles at 0.5 C,and the single-cycle capacity decay rate was only 0.01%.When the Li-Li battery was cycled for 1000 hours at 1 m A cm^-2,the voltage amplitude remained within±0.1V.These were attributed to the strong lithium dendrite carrying capacity of the micro-mesoporous structure and the ability of YF₃ to induce uniform lithium deposition.