Forging Inspired Processing of Sodium-Fluorinated Graphene Composite as Dendrite-Free Anode for Long-Life Na–CO_(2) Cells

Na–CO_(2) batteries recently are emerging as promising energy-storage devices due to the abundance of Na in the earth’s crust and the clean utilization of greenhouse gas CO_(2) .However,similar to metallic Li,metallic Na also suffers from a serious issue of dendrite growth upon repeated cycling,while a facile method to solve this issue is still lacking.In this work,we report an effective,environmentally friendly method to inhibit Na dendrite growth by in situ constructing a stable,NaF-rich solid electrolyte interface(SEI)layer on metallic Na via adding a small amount(~3 wt%)of fluorinated graphene(FG)in bulk Na.Inspired by the forging processing,a uniform Na/FG composite was obtained by melting and repetitive FG-adsorbing/hammering processes.The Na/FG–Na/FG half cell exhibits a low voltage hysteresis of 110–140 mV over 700 h at a current density up to 5 mA cm^(-2) with an areal capacity as high as 5 mAh cm^(-2).Na–CO_(2) full cell with the Na/FG anode is able to sustain a stable cycling of 391 cycles at a limited capacity of 1000 mAh g^(-1).Long cycle life of the cell can be attributed to the protecting effect of the in situ fabricated NaF-rich SEI layer on metallic Na.Both experiments and density functional theory(DFT)calculations confirm the formation of the NaF-rich SEI layer.The inhibition effect of the NaF-rich SEI layer for Na dendrites is verified by in situ optical microscopy observations.

Fluorinated graphene quantum dots with long-term lubrication for visual drug loading and joint inflammation therapy

Osteoarthritis(OA)treatment mainly relies on developing new drugs or nanocarriers,while little attention is paid to building novel remedial mode and improving drug loading efficiency.This work reports an integrated nanosystem that not only realizes visual drug loading and release,but also achieves enhanced lubrication and effective joint inflammation therapy based on fluorinated graphene quantum dots(FGQDs).Oxygen introduction promotes FGQDs outstanding water-stability for months,and layered nano-sized structure further guarantees excellent lubricating properties in biomimetic synovial fluid.The special design of chemistry and structure endows FGQDs robust fluorescence in a wide range of pH conditions.Also,the excitation spectrum of FGQDs well overlaps the absorption spectrum of drugs,which further constructs a new concept of internal filtering system to visually monitor drug loading by naked eyes.More importantly,extraordinary long-term lubrication performance is reported,which is the first experimental demonstration of concentration-dependent mutations of coefficient of friction(COF).Cell incubation experiments indicate that drug-loaded FGQDs have good biocompatibility,tracking property of cellular uptake and drug release,which show efficient anti-inflammation potential for H2O2-induced chondrocyte degradation by up-regulated cartilage anabolic genes.This study establishes a promising OA treatment strategy that enables to monitor drug loading and release,to enhance long-time lubricating property,and to show effective anti-inflammatory potential for cartilage protection.

Multi-layered fluorinated graphene cathode materials for lithium and sodium primary batteries

Fluorinated graphene has a promising application prospect in lithium primary batteries(LPBs)and sodium primary batteries(SPBs).Herein,five fluorinated graphene materials with different fluorine contents(FG-x)are prepared by a large-scale gas fluorination process.It is found that the structural characteristics of FG-x strongly depend on the fluorination temperature:the fluorine content(i.e.,F/C ratio)gradually increases with the fluorination temperature rising,resulting in the enlargement of interlayer spacing and the increase of average bonding strength between C and F.FG-0.75 sample with the intermediate degree of fluorination achieves the maximum energy densities in LPBs(2239.8 Wh·kg^(-1))and SPBs(1939.2 Wh·kg^(-1)).The interlayer distance is critical to the rate capability of FG-x,and FG-0.95 with the largest lattice spacing exhibits the best rate performance in both Li/CFx and Na/CFx batteries.The electrochemical reaction mechanism and the structural evolution of FG material revealed by ex situ X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD)characterization,and in situ Raman spectra further confirm the effect of interlayer distance.

Fluorinated graphene nanoribbons from unzipped single-walled carbon nanotubes for ultrahigh energy density lithium-fluorinated carbon batteries

Lithium-fluorinated carbon(Li-CFx)batteries have become one of the most widely applied power sources for high energy density applications because of the advantages provided by the CFx cathode.Moreover,the large gap between the practical and theoretical potentials alongside the stoichiometric limit of commercial graphite fluorides indicates the potential for further energy improvement.Herein,monolayer fluorinated graphene nanoribbons(F-GNRs)were fabricated by unzipping single-walled carbon nanotubes(SWCNTs)using pure F2 gas at high temperature,which delivered an unprecedented energy density of 2738.45 W h kg^(−1)due to the combined effect of a high fluorination degree and discharge plateau,realized by the abundant edges and destroyed periodic structure,respectively.Furthermore,at a high fluorination temperature,the theoretical calculation confirmed a zigzag pathway of fluorine atoms that were adsorbed outside of the SWCNTs and hence initiated the spontaneous process of unzipping SWCNTs to form the monolayer F-GNRs.The controllable fluorination of SWCNTs provided a feasible approach for preparing CFx compounds for different applications,especially for ultrahigh-energy-density cathodes.

Patterning Nanoroads and Quantum Dots on Fluorinated Graphene

Using ab initio methods we have investigated the fluorination of graphene and find that different stoichiometric phases can be formed without a nucleation barrier, with the complete ＂2D-Teflon＂ CF phase being thermody- namically most stable. The fluorinated graphene is an insulator and turns out to be a perfect matrix-host for patterning nanoroads and quantum dots of pristine graphene. The electronic and magnetic properties of the nanoroads can be tuned by varying the edge orientation and width. The energy gaps between the highest occupied and lowest unoccupied molecular orbitals （HOMO-LUMO） of quantum dots are size-dependent and show a confinement typical of Dirac fermions. Furthermore, we study the effect of different basic coverage of F on graphene （with stoichiometries CF and C4F） on the band gaps, and show the suitability of these materials to host quantum dots of graphene with unique electronic properties.

The Fluorination of Boron-Doped Graphene for CF_(x) Cathode with Ultrahigh Energy Density

The enhancement of the fluorination degree of carbon fluorides(CF_(x))compounds is the most effective method to improve the energy densities of Li/CF_(x)batteries because the specific capacity of CF_(x)is proportional to the molar ratio of F to C atoms(F/C).In this study,B-doped graphene(BG)is prepared by using boric acid as the doping source and then the prepared BG is utilized as the starting material for the preparation of CF_(x).The B-doping enhances the F/C ratio of CF_(x)without hindering the electrochemical activity of the C–F bond.During the fluorination process,B-containing functional groups are removed from the graphene lattice.This facilitates the formation of a defect-rich graphene matrix,which not only enhances the F/C ratio due to abundant perfluorinated groups at the defective edges but also serves as the active site for extra Li+storage.The prepared CF_(x)exhibits the maximum specific capacity of 1204 mAh g^(−1),which is 39.2%higher than that of CF_(x)obtained directly from graphene oxide(without B-doping).An unprecedented energy density of 2974 Wh kg^(−1)is achieved for the asprepared CF_(x)samples,which is significantly higher than the theoretically calculated energy density of commercially available fluorinated graphite(2180 Wh kg^(−1)).Therefore,this study demonstrates a great potential of B-doping to realize the ultrahigh energy density of CF_(x)cathodes for practical applications.

Facile and secure synthesis of porous partially fluorinated graphene employing weakly coordinating anion for enhanced high-performance symmetric supercapacitor

In this paper,porous partially fluorinated graphene(PFG)for supercapacitors(SCs)was fabricated by a mild and secure one-pot hydrothermal method utilizing weakly coordinating anion BF_(4)^(-) as the fluorine source.The hydrolysis rate of sodium fluoroborate was adjusted by controlling the reaction temperature and PFG containing semi-ionic C-F bonds was obtained,where the content of semi-ionic C-F bonds in PFG can be easily regulated.The final experimental results show that the incorporation of fluorine not only modulates the electrochemical properties of the material,but also creates abundant pores.When assembled in a symmetric supercapacitor,the PFG shows a high specific capacitance of 269.7 F g^(-1) at 1 A g^(-1) and a superior rate capability with 89.3%capacitance retained,as the current density is increased from 1 A g^(-1)even to 20 A g^(-1).Furthermore,the resultant energy density for PFG is 9.4 Wh kg^(-1) at a power density of 250.0 W kg^(-1)(1 A g^(-1)).All these results confirm that as-prepared partially fluorinated graphene is appropriate for the application in SCs and mass production.