Edge‐Fluorinated Graphene Nanoplatelets as High Performance Electrodes for Dye‐Sensitized Solar Cells and Lithium Ion Batteries

Abstract

Edge‐selectively fluorinated graphene nanoplatelets (FGnPs) are prepared by mechanochemically driven reaction between fluorine gas (20 vol% in argon) and activated carbon species from graphitic C–C bonds unzipped by high‐speed stainless steel balls with a high kinetic energy. The fluorination at edges of the unzipped graphene nanoplatelets (GnPs) is confirmed by various analytical techniques while the content of fluorine in FGnPs is determined to be 3.0 and 3.4 at% by X‐ray photoelectron spectroscopy and energy‐dispersive X‐ray spectroscopy, respectively. Because of the large difference in electronegativity between carbon (χ = 2.55) and fluorine (χ = 3.98) and the strong C–F bond, the edge‐fluorination of GnPs can provide the maximized charge polarization with an enhanced chemical stability. Thus, electrodes based on the resultant FGnPs demonstrate superb electrochemical performance with excellent stability/cycle life in dye‐sensitized solar cells (FF: 71.5%; Jsc: 14.44 mA cm−2; Voc: 970 mV; PCE: 10.01%) and lithium ion batteries (650.3 mA h g−1 at 0.5 C, charge retention of 76.6% after 500 cycles).

Halide‐Based Materials and Chemistry for Rechargeable Batteries

“…3at% fluorine), which were prepared by as imilar ball milling in afluorine (F 2 )atmosphere,indicated that ahigher reversible capacity of about 500 mAh g À1 was maintained after 500 cycles,w hich is higher than the result for the iodine-doped GnPs. [130] This finding was ascribed to the maximized charge polarization and enhanced chemical stability achieved by fluorine doping.Huang et al reported that Nand Fcodoping in graphene produced excellent rate capabilities,with areversible capacity of 305 mAh g À1 and acapacity retention of 95 % after 2000 cycles at 5Ag À1 . [131] In addition to the synergetic effects of the codoping,t he formation of the semi-ionic CÀF bonds,i nw hich carbon atoms retain the original sp 2 hybridization, ensures the high electrical conductivity,a nd the existence of the strong covalent C À Fb onds leads to the formation of adense SEI in the first cycle.…”

Mechanochemistry of Gaseous Reactants

“…Such milling conditions induced homolytic and heterolytic cleavage of the graphitic CÀCb onds and the generation of carbon radicals and ions.T hese species reacted with CO 2 ,a nd exposure to air (oxygen and water) afforded oxygenated groups,s uch as hydroxy (-OH) and carboxylic acid (-COOH) groups.T he edge-attached functional carboxylic acid groups repelled each other to facilitate self-exfoliation of the graphite to give single or few-layers of graphene nanoplatelets (Figure 4d). [40] Following this mechanochemical procedure,t he same research group and others extended the exfoliation of graphite to reactions with hydrogen (H 2 ), [41] volatile sulfur trioxide (SO 3 ), [41] chlorine (Cl 2 ), [42] fluorine (F 2 ), [43] nitrogen (N 2 ), [44] dichlorine monoxide (Cl 2 O), [45] among other gaseous reagents. [46] In general, this mechanical treatment inside pressurized ball mills overcame the limitation of working with poorly soluble graphite and graphene.…”

Mechanochemie gasförmiger Reaktanten

“…[40] Diesem mechanochemischen Protokoll folgend erweiterten diese und weitere Forschungsgruppen das Abblättern von Graphit durch Reaktionen mit Wasserstoff (H 2 ), [41] flüchtigem Schwefeltrioxid (SO 3 ), [41] Chlor (Cl 2 ), [42] Fluor (F 2 ), [43] Stickstoff (N 2 ), [44] Dichlormonoxid (Cl 2 O) und weiteren gasfçrmigen Reaktanten. Die am Rand lokalisierten funktionellen Carbonsäuregruppen stießen einander ab und erleichterten die Selbstabblätterung des Graphits,was zu einzelnen oder wenige Schichten dicke Graphennanoplättchen führte (Abbildung 4d).…”

“…Die am Rand lokalisierten funktionellen Carbonsäuregruppen stießen einander ab und erleichterten die Selbstabblätterung des Graphits,was zu einzelnen oder wenige Schichten dicke Graphennanoplättchen führte (Abbildung 4d). [40] Diesem mechanochemischen Protokoll folgend erweiterten diese und weitere Forschungsgruppen das Abblättern von Graphit durch Reaktionen mit Wasserstoff (H 2 ), [41] flüchtigem Schwefeltrioxid (SO 3 ), [41] Chlor (Cl 2 ), [42] Fluor (F 2 ), [43] Stickstoff (N 2 ), [44] Dichlormonoxid (Cl 2 O) und weiteren gasfçrmigen Reaktanten. [45,46] Allgemein überwand die mechanische Behandlung in unter Druck stehenden Kugelmühlen die Limitierung des Arbeitens mit schlecht lçslichem Graphit und Graphen.…”