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2016 Volume 74 Issue 10
2016, 74(10): 789-799
doi: 10.6023/A16070360
Abstract:
Graphene and graphene oxide have attracted tremendous interest over the past decade due to their unique electronic, optical, mechanical, and chemical properties. Pristine graphene is desirable for applications that require a high electrical conductivity, while many other applications require modified or functionalized forms such as graphene oxide due to its good dispersibility in various solvents. Surface functional modification of graphene and graphene oxide is of crucial importance for their broad applications. Functionalization of graphene enables this material to be processed by solvent assisted techniques, such as layer-by-layer assembly, filtration. It also prevents the agglomeration of single layer graphene and maintains the inherent properties. Structurally modifying graphene and graphene oxide through chemical functionalization reveals the numerous possibilities for tuning its structure. Several chemical and physical functionalization methods have been explored to improve the stabilization and modification of graphene. This review focuses on the surface functional modification of graphene and graphene oxide. The preparation method, basic structure and properties of graphene and graphene oxide were briefly described firstly. On the one hand, in the light of bonding characteristic, the surface functionalization of graphene and graphene oxide is divided into non-covalent binding modification, covalent binding modification and elemental doping. On the other hand, non-covalent functionalization contains four categories: π-π stacking, hydrogen bonding, ionic bonding effect and electrostatic interaction. Meanwhile, covalently functionalization includes four categories: carbon skeleton modification, hydroxy modification, carboxy modification and epoxy group modification due to the reactive functional groups. Doping functionalization consists of N, B, P and other different elements. According to the classification of surface structure characteristics, selected typical case has described the functional modification process in detail. The properties and application prospects of the modified products are also summarized. Finally, current challenges and future research directions are also presented in terms of surface functional modification for graphene and graphene oxide.
Graphene and graphene oxide have attracted tremendous interest over the past decade due to their unique electronic, optical, mechanical, and chemical properties. Pristine graphene is desirable for applications that require a high electrical conductivity, while many other applications require modified or functionalized forms such as graphene oxide due to its good dispersibility in various solvents. Surface functional modification of graphene and graphene oxide is of crucial importance for their broad applications. Functionalization of graphene enables this material to be processed by solvent assisted techniques, such as layer-by-layer assembly, filtration. It also prevents the agglomeration of single layer graphene and maintains the inherent properties. Structurally modifying graphene and graphene oxide through chemical functionalization reveals the numerous possibilities for tuning its structure. Several chemical and physical functionalization methods have been explored to improve the stabilization and modification of graphene. This review focuses on the surface functional modification of graphene and graphene oxide. The preparation method, basic structure and properties of graphene and graphene oxide were briefly described firstly. On the one hand, in the light of bonding characteristic, the surface functionalization of graphene and graphene oxide is divided into non-covalent binding modification, covalent binding modification and elemental doping. On the other hand, non-covalent functionalization contains four categories: π-π stacking, hydrogen bonding, ionic bonding effect and electrostatic interaction. Meanwhile, covalently functionalization includes four categories: carbon skeleton modification, hydroxy modification, carboxy modification and epoxy group modification due to the reactive functional groups. Doping functionalization consists of N, B, P and other different elements. According to the classification of surface structure characteristics, selected typical case has described the functional modification process in detail. The properties and application prospects of the modified products are also summarized. Finally, current challenges and future research directions are also presented in terms of surface functional modification for graphene and graphene oxide.
2016, 74(10): 800-804
doi: 10.6023/A16070358
Abstract:
The Rauhut-Currier (R-C) reaction, first disclosed by Rauhut and Currier in 1963, is an atom economy strategy for the construction of carbon-carbon bond and a wide range of synthetic valuable building blocks. During the past few decades, significant progress on the enantioselective intramolecular R-C reactions has been achieved by utilizing diverse chiral nucleophilic catalysts such as cysteine derivatives, L-prolinol, hydrogen-bonding catalyst and β-aminephosphine. However, compared to the well-developed enantioselective intramolecular R-C reactions, the enantioselective cross intermolecular R-C reaction concerning two different alkenes has been rarely explored so far. The enantioselective cross R-C reaction still suffers from a series of drawbacks such as low reactivity, enantioselectivity, limited substrate scope and higher catalyst loading. Thus, the development of novel chiral nucleophilic catalyst, for highly enantioselective cross R-C reaction is highly desirable. In this article, we wish to report the application of Xiao-Phos in the highly enantioselective cross intermolecular R-C reaction of vinyl ketone and activated alkenes. Accordingly, a stirred solution of 3-aroyl acrylates 1 (0.2 mmol) and (S,RS)-X8 (0.02 mmol) in toluene (2 mL) was cooled to -20℃. Subsequently, vinyl ketone 2 (0.4 mmol for aryl vinyl ketone and 0.6 mmol for alkyl vinyl ketone) was added in one portion through a syringe. The mixture was stirred at this temperature until completion of 3-aroyl acrylate as indicated by TLC. After completion of the reaction, the reaction mixture was directly purified by silica gel chromatography to afford the desired RC product. What’s more, control experiments demonstrated that the presence of free sulfinamide N-H in Xiao-Phos is crucial for the enantioselective cross R-C reaction. Finally, for more details about (S,RS)-X8 in the enantioselective cross R-C reaction, control experiments monitored by 31P NMR spectroscopy were conducted and the 31P NMR experiments indicated that this cross intermolecular R-C reaction was initiated by the Michael addition of (S,RS)-X8 to vinyl ketone 2.
The Rauhut-Currier (R-C) reaction, first disclosed by Rauhut and Currier in 1963, is an atom economy strategy for the construction of carbon-carbon bond and a wide range of synthetic valuable building blocks. During the past few decades, significant progress on the enantioselective intramolecular R-C reactions has been achieved by utilizing diverse chiral nucleophilic catalysts such as cysteine derivatives, L-prolinol, hydrogen-bonding catalyst and β-aminephosphine. However, compared to the well-developed enantioselective intramolecular R-C reactions, the enantioselective cross intermolecular R-C reaction concerning two different alkenes has been rarely explored so far. The enantioselective cross R-C reaction still suffers from a series of drawbacks such as low reactivity, enantioselectivity, limited substrate scope and higher catalyst loading. Thus, the development of novel chiral nucleophilic catalyst, for highly enantioselective cross R-C reaction is highly desirable. In this article, we wish to report the application of Xiao-Phos in the highly enantioselective cross intermolecular R-C reaction of vinyl ketone and activated alkenes. Accordingly, a stirred solution of 3-aroyl acrylates 1 (0.2 mmol) and (S,RS)-X8 (0.02 mmol) in toluene (2 mL) was cooled to -20℃. Subsequently, vinyl ketone 2 (0.4 mmol for aryl vinyl ketone and 0.6 mmol for alkyl vinyl ketone) was added in one portion through a syringe. The mixture was stirred at this temperature until completion of 3-aroyl acrylate as indicated by TLC. After completion of the reaction, the reaction mixture was directly purified by silica gel chromatography to afford the desired RC product. What’s more, control experiments demonstrated that the presence of free sulfinamide N-H in Xiao-Phos is crucial for the enantioselective cross R-C reaction. Finally, for more details about (S,RS)-X8 in the enantioselective cross R-C reaction, control experiments monitored by 31P NMR spectroscopy were conducted and the 31P NMR experiments indicated that this cross intermolecular R-C reaction was initiated by the Michael addition of (S,RS)-X8 to vinyl ketone 2.
2016, 74(10): 805-810
doi: 10.6023/A16060316
Abstract:
The direct activation and functionalization of C-H bonds is fundamentally important in organic synthesis. Among different methods developed, transition metal-catalyzed intermolecular arylation of alkanes, which couples unactivated C(sp3)-H bonds with aryl moieties, is recognized as one of the most powerful strategies to construct valuable arylated alkyl scaffolds. Tremendous progress has thus been made in this field, which usually require harsh reaction conditions such as high temperature and inert atmosphere as well as additives. Furthermore, the reaction media were usually organic solvents with undesirable toxicity and volatility, such as toluene, xylene, tert-amyl alcohol, dichloroethane, etc. Therefore, the development of efficient catalytic unactivated C(sp3)-H arylation under mild reaction conditions is still highly demanded. Herein, we reported a general and practical palladium-catalyzed arylation of β-methylene C(sp3)-H under aqueous conditions by the use of 8-aminoquinoline as directing groups. This method exhibited good to excellent yields up to 96% and good functional group tolerance without other additives and inert gas atmosphere. Meanwhile, the reaction showed good regioselectivity to the β-position of carbonyl group. Mechanism studies showed that the aliphatic Ag-carboxylate salt was critical for this reaction. The silver ion might weaken the C-I bond and function as halogen scavenger for the transformation, while pivalic acid ion might act as base during reaction. A representative procedure for this reaction is as following: To a 10 mL glass tube, N-(quinolin-8-yl) butyramide (42.8 mg, 0.2 mmol), iodobenzene (67 μL, 0.4 mmol), Pd(OAc)2 (4.5 mg), AgPiv (83.6 mg, 0.4 mmol) in 0.4 mL H2O were stirred at 60℃ for 24 h, and then cooled to room temperature. The reaction mixture was extracted with EtOAc. The organic phase was washed with water, dried over magnesium sulfate, and concentrated. The crude product was purified with column chromatography (petroleum/EtOAc) to provide the products in 61%~96% yields.
The direct activation and functionalization of C-H bonds is fundamentally important in organic synthesis. Among different methods developed, transition metal-catalyzed intermolecular arylation of alkanes, which couples unactivated C(sp3)-H bonds with aryl moieties, is recognized as one of the most powerful strategies to construct valuable arylated alkyl scaffolds. Tremendous progress has thus been made in this field, which usually require harsh reaction conditions such as high temperature and inert atmosphere as well as additives. Furthermore, the reaction media were usually organic solvents with undesirable toxicity and volatility, such as toluene, xylene, tert-amyl alcohol, dichloroethane, etc. Therefore, the development of efficient catalytic unactivated C(sp3)-H arylation under mild reaction conditions is still highly demanded. Herein, we reported a general and practical palladium-catalyzed arylation of β-methylene C(sp3)-H under aqueous conditions by the use of 8-aminoquinoline as directing groups. This method exhibited good to excellent yields up to 96% and good functional group tolerance without other additives and inert gas atmosphere. Meanwhile, the reaction showed good regioselectivity to the β-position of carbonyl group. Mechanism studies showed that the aliphatic Ag-carboxylate salt was critical for this reaction. The silver ion might weaken the C-I bond and function as halogen scavenger for the transformation, while pivalic acid ion might act as base during reaction. A representative procedure for this reaction is as following: To a 10 mL glass tube, N-(quinolin-8-yl) butyramide (42.8 mg, 0.2 mmol), iodobenzene (67 μL, 0.4 mmol), Pd(OAc)2 (4.5 mg), AgPiv (83.6 mg, 0.4 mmol) in 0.4 mL H2O were stirred at 60℃ for 24 h, and then cooled to room temperature. The reaction mixture was extracted with EtOAc. The organic phase was washed with water, dried over magnesium sulfate, and concentrated. The crude product was purified with column chromatography (petroleum/EtOAc) to provide the products in 61%~96% yields.
2016, 74(10): 811-818
doi: 10.6023/A16070351
Abstract:
Mn(OAc)3-mediated selective radical phosphorylation of indoles with dialkylphosphites or diphenylphosphine oxide in moderate to good yields is described. The reaction proceeds under mild conditions in air, no need to add extra additives, through a radical process involving phosphorus-centered radical generated from dialkylphosphites or diphenylphosphine oxide mediated by Mn(OAc)3, selectively added to 3-position of 2-substituted indoles or 2-position of 3-substituted indoles to form carbon radical intermediate, followed by oxidation with Mn(OAc)3 and deprotonation to afford products 2- or 3-phosphonyl indoles. This protocol provides an efficient and general method for the preparation of 2- and 3-phosphoryl indoles. The detailed investigation revealed that 1) the yields of N-methyl indoles were higher than NH unprotected analogues; 2) 2-Phenyl or 2-methyl indoles were unsuitable for the reaction with dialkylphosphites, but were suitable for the reaction with diphenyl phosphine oxide; 3) Indoles bearing electron-withdrawing groups such as F, Cl, Br on the phenyl ring were favored to the reaction. A representative procedure for this reaction is as follows: To a solution of substituted indoles 1 or 4 (1 mmol) and dialkylphosphites 2 (2 mmol) in HOAc (3 mL) heated with oil bath (50℃), Mn(OAc)3 (3 mmol) was added in portions within 0.5 h, then, the mixture was allowed to stir further for 0.5 h. After removal of the most solvent under reduced pressure, 50 mL water was added to the residue and the mixture was extracted with EtOAc (20 mL×3). The combined organic layers were dried over anhydrous Na2SO4, filtered, concentrated under reduced pressure, and the residue was purified by flash silica-gel column chromatography (using mixture of petroleum ether/ethyl acetate as eluent from ratio of 20/1 to 1/2) to afford the desired 2- or 3-phosphonyl indoles 3 or 5.
Mn(OAc)3-mediated selective radical phosphorylation of indoles with dialkylphosphites or diphenylphosphine oxide in moderate to good yields is described. The reaction proceeds under mild conditions in air, no need to add extra additives, through a radical process involving phosphorus-centered radical generated from dialkylphosphites or diphenylphosphine oxide mediated by Mn(OAc)3, selectively added to 3-position of 2-substituted indoles or 2-position of 3-substituted indoles to form carbon radical intermediate, followed by oxidation with Mn(OAc)3 and deprotonation to afford products 2- or 3-phosphonyl indoles. This protocol provides an efficient and general method for the preparation of 2- and 3-phosphoryl indoles. The detailed investigation revealed that 1) the yields of N-methyl indoles were higher than NH unprotected analogues; 2) 2-Phenyl or 2-methyl indoles were unsuitable for the reaction with dialkylphosphites, but were suitable for the reaction with diphenyl phosphine oxide; 3) Indoles bearing electron-withdrawing groups such as F, Cl, Br on the phenyl ring were favored to the reaction. A representative procedure for this reaction is as follows: To a solution of substituted indoles 1 or 4 (1 mmol) and dialkylphosphites 2 (2 mmol) in HOAc (3 mL) heated with oil bath (50℃), Mn(OAc)3 (3 mmol) was added in portions within 0.5 h, then, the mixture was allowed to stir further for 0.5 h. After removal of the most solvent under reduced pressure, 50 mL water was added to the residue and the mixture was extracted with EtOAc (20 mL×3). The combined organic layers were dried over anhydrous Na2SO4, filtered, concentrated under reduced pressure, and the residue was purified by flash silica-gel column chromatography (using mixture of petroleum ether/ethyl acetate as eluent from ratio of 20/1 to 1/2) to afford the desired 2- or 3-phosphonyl indoles 3 or 5.
2016, 74(10): 819-824
doi: 10.6023/A16070349
Abstract:
Chiral metal-organic framework materials, as a new type of porous materials, have attracted much attention in the field of chiral separation. In this paper, a homochiral MOF [Cu(S-mal)(bpy)]n with 3D chiral networks was synthesized by the reaction of ligands (S-malic acid and 4,4'-bipyridine) with copper acetate via a solvothermal method. A packed chiral column for high performance liquid chromatography was fabricated using [Cu(S-mal)(bpy)]n as stationary phase. Before the packing, the MOF crystals was crushed in ethanol applying soft pressure and then the MOF with suitable particle size (5~10 m) was obtained via solvent suspension. A 4.2 g mass of prepared MOF was suspended in a mixture of hexane and isopropanol. In order to control the packing quality, the suspension of MOF was packed into a stainless steel empty column (25 cm long×4.6 mm i.d.) under 40 MPa using hexane/isopropanol (9:1, V/V) as the slurry solvent according to a conventional high pressure slurry packing procedure. To investigate the chiral recognition ability of this stationary phase, a series of racemic compounds were separated on the chiral MOF column using different ratio of n-hexane/isopropanol as mobile phase. The results showed that the chiral column exhibited good resolving ability towards 17 racemates, including alcohols, ketones, flavonoids, phenols and amines. For instance, the resolution value of 1-(1-naphthyl)ethanol could reach 4.5. Compared with three kinds of homochiral MOFs columns previously reported by our group, this column showed better chiral recognition ability and higher resolution toward racemates, and has a good complementary for chiral separation. The [Cu(S-mal)(bpy)]n possesses cavities with average dimensions (5 Å×5 Å×6 Å), which were interconnected by narrow windows with diameter ≤3 Å. Therefore, the chiral recognition mostly depends on the surface of the MOF crystal in which the steric fit between the chiral networks and conformation of the solute molecule is the main interactive force. Besides, many other interactions such as the hydro-gen-bondings, dispersion forces, dipole-dipole interaction, and π-π interactions which come from the solutes, chiral stationary phase and the mobile phase may also play some role. The reproducibility and stability of the chiral column were evaluated. The results showed that the chiral column showed good reproducibility and stability for enantioseparation.
Chiral metal-organic framework materials, as a new type of porous materials, have attracted much attention in the field of chiral separation. In this paper, a homochiral MOF [Cu(S-mal)(bpy)]n with 3D chiral networks was synthesized by the reaction of ligands (S-malic acid and 4,4'-bipyridine) with copper acetate via a solvothermal method. A packed chiral column for high performance liquid chromatography was fabricated using [Cu(S-mal)(bpy)]n as stationary phase. Before the packing, the MOF crystals was crushed in ethanol applying soft pressure and then the MOF with suitable particle size (5~10 m) was obtained via solvent suspension. A 4.2 g mass of prepared MOF was suspended in a mixture of hexane and isopropanol. In order to control the packing quality, the suspension of MOF was packed into a stainless steel empty column (25 cm long×4.6 mm i.d.) under 40 MPa using hexane/isopropanol (9:1, V/V) as the slurry solvent according to a conventional high pressure slurry packing procedure. To investigate the chiral recognition ability of this stationary phase, a series of racemic compounds were separated on the chiral MOF column using different ratio of n-hexane/isopropanol as mobile phase. The results showed that the chiral column exhibited good resolving ability towards 17 racemates, including alcohols, ketones, flavonoids, phenols and amines. For instance, the resolution value of 1-(1-naphthyl)ethanol could reach 4.5. Compared with three kinds of homochiral MOFs columns previously reported by our group, this column showed better chiral recognition ability and higher resolution toward racemates, and has a good complementary for chiral separation. The [Cu(S-mal)(bpy)]n possesses cavities with average dimensions (5 Å×5 Å×6 Å), which were interconnected by narrow windows with diameter ≤3 Å. Therefore, the chiral recognition mostly depends on the surface of the MOF crystal in which the steric fit between the chiral networks and conformation of the solute molecule is the main interactive force. Besides, many other interactions such as the hydro-gen-bondings, dispersion forces, dipole-dipole interaction, and π-π interactions which come from the solutes, chiral stationary phase and the mobile phase may also play some role. The reproducibility and stability of the chiral column were evaluated. The results showed that the chiral column showed good reproducibility and stability for enantioseparation.
2016, 74(10): 825-832
doi: 10.6023/A16050256
Abstract:
In this work, for the first time, three-component CeO2@Ag@CdSe heterostructured nanotube arrays with remarkable photoelectrochemical (PEC) properties have been synthesized on the FTO conductive glass substrate by an electrodeposition method. One-dimensional vertically ordered CeO2 nanotube arrays were prepared on the FTO substrate by electrodeposition method with Ce(NO3)2·6H2O and C2H6SO as the raw materials. Ag nanoparticles were deposited on the surface of CeO2 nanotube arrays through a successive electrodeposition in a solution of AgNO3, and a composite system of CeO2@Ag was obtained. Then a thin CdSe layer was deposited and covered on the CeO2@Ag system to form three-component CeO2@Ag@CdSe heterostructured nanotube arrays. The as-synthesized products were characterized using X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The PEC properties of the obtained products were recorded with electrochemical workstation, and the results showed that the CdSe layer could greatly enhance light harvesting and significantly improve charge separation. Moreover, the modification with Ag nanoparticles can significantly strengthen the light-harvesting ability through the localized surface plasma resonance effect and provide an interior direct pathway to facilitate the separation and transport of photogenerated carriers. It has been demonstrated that the enhanced PEC properties of CeO2@Ag@CdSe heterostructures are direct consequence of the synergetic effects of enhanced visible light absorption and the effective separation and transportation of photogenerated carriers at interface of type-II heterostructure via the Ag nanoparticles. Therefore, the CeO2@Ag@CdSe heterostructured nanotubes generate a remarkable photocurrent density of 3.92 mA·cm-2 at a potential of -0.2 V (vs. Ag/AgCl), which is 4.9 and 17.9 times higher than that of two-component CeO2@CdSe (0.802 mA·cm-2) and CeO2@Ag (0.218 mA·cm-2) systems, respectively. It also gives an incident photon to current conversion efficiency (IPCE) as high as 72% at around 360 nm. Moreover, the photoelectrode shows high photostability during the test period over 16 min.
In this work, for the first time, three-component CeO2@Ag@CdSe heterostructured nanotube arrays with remarkable photoelectrochemical (PEC) properties have been synthesized on the FTO conductive glass substrate by an electrodeposition method. One-dimensional vertically ordered CeO2 nanotube arrays were prepared on the FTO substrate by electrodeposition method with Ce(NO3)2·6H2O and C2H6SO as the raw materials. Ag nanoparticles were deposited on the surface of CeO2 nanotube arrays through a successive electrodeposition in a solution of AgNO3, and a composite system of CeO2@Ag was obtained. Then a thin CdSe layer was deposited and covered on the CeO2@Ag system to form three-component CeO2@Ag@CdSe heterostructured nanotube arrays. The as-synthesized products were characterized using X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The PEC properties of the obtained products were recorded with electrochemical workstation, and the results showed that the CdSe layer could greatly enhance light harvesting and significantly improve charge separation. Moreover, the modification with Ag nanoparticles can significantly strengthen the light-harvesting ability through the localized surface plasma resonance effect and provide an interior direct pathway to facilitate the separation and transport of photogenerated carriers. It has been demonstrated that the enhanced PEC properties of CeO2@Ag@CdSe heterostructures are direct consequence of the synergetic effects of enhanced visible light absorption and the effective separation and transportation of photogenerated carriers at interface of type-II heterostructure via the Ag nanoparticles. Therefore, the CeO2@Ag@CdSe heterostructured nanotubes generate a remarkable photocurrent density of 3.92 mA·cm-2 at a potential of -0.2 V (vs. Ag/AgCl), which is 4.9 and 17.9 times higher than that of two-component CeO2@CdSe (0.802 mA·cm-2) and CeO2@Ag (0.218 mA·cm-2) systems, respectively. It also gives an incident photon to current conversion efficiency (IPCE) as high as 72% at around 360 nm. Moreover, the photoelectrode shows high photostability during the test period over 16 min.
2016, 74(10): 833-838
doi: 10.6023/A16080394
Abstract:
In the past few decades, lithium hexafluorophosphate (LiPF6) is the most widely employed ionic component in organic electrolyte solutions for commercial lithium ion battery, which is manufactured using PCl5, LiF and HF as raw materials via the HF solvent method in the large scale production, and then it commonly contains LiF and LiCl impurities besides water and acid. However, the influence of LiF and LiCl on the performance of lithium ion battery is still not clear. Thus, in this paper, the influence of LiF and LiCl on the electrochemical performance of graphite electrode was investigated using charge-discharge test and cyclic voltammetry (CV) combining with scanning electron microscope (SEM) and electrochemical impedance spectrum (EIS). Charge-discharge test results showed that the electrochemical performance of graphite electrode such as reversible capacity and cycling stability were significantly improved in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF. The initial charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF is 331.0 mAh/g, which is higher than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte (307.9 mAh/g). After 65 charge-discharge cycles, the charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF is 340.1 mAh/g, which is also higher than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte (297.0 mAh/g). However, although the first charging capacity of graphite electrode was enhanced in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl, the charge-discharge cycling stability was serious deteriorated. The initial charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl is 334.2 mAh/g, yet after 65 charge-discharge cycles, the charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl is 251.2 mAh/g. CV results showed that the influence of LiF and LiCl on the decomposition process of EC in electrolyte is small. SEM and EIS results stated that the SEI film which was formed on the graphite electrode is thinner and has a smaller resistance in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte. Thus the reversible cycle capacity of graphite electrode was increased and its cycle stability was improved. Nevertheless the SEI film which was formed on the graphite electrode is thicker and its resistance is higher in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte, which leads to the deterioration of electrochemical performance of graphite electrode.
In the past few decades, lithium hexafluorophosphate (LiPF6) is the most widely employed ionic component in organic electrolyte solutions for commercial lithium ion battery, which is manufactured using PCl5, LiF and HF as raw materials via the HF solvent method in the large scale production, and then it commonly contains LiF and LiCl impurities besides water and acid. However, the influence of LiF and LiCl on the performance of lithium ion battery is still not clear. Thus, in this paper, the influence of LiF and LiCl on the electrochemical performance of graphite electrode was investigated using charge-discharge test and cyclic voltammetry (CV) combining with scanning electron microscope (SEM) and electrochemical impedance spectrum (EIS). Charge-discharge test results showed that the electrochemical performance of graphite electrode such as reversible capacity and cycling stability were significantly improved in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF. The initial charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF is 331.0 mAh/g, which is higher than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte (307.9 mAh/g). After 65 charge-discharge cycles, the charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF is 340.1 mAh/g, which is also higher than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte (297.0 mAh/g). However, although the first charging capacity of graphite electrode was enhanced in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl, the charge-discharge cycling stability was serious deteriorated. The initial charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl is 334.2 mAh/g, yet after 65 charge-discharge cycles, the charge capacity of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl is 251.2 mAh/g. CV results showed that the influence of LiF and LiCl on the decomposition process of EC in electrolyte is small. SEM and EIS results stated that the SEI film which was formed on the graphite electrode is thinner and has a smaller resistance in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiF than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte. Thus the reversible cycle capacity of graphite electrode was increased and its cycle stability was improved. Nevertheless the SEI film which was formed on the graphite electrode is thicker and its resistance is higher in 1 mol/L LiPF6-EC:DEC:DMC electrolyte with the saturation of LiCl than that in 1 mol/L LiPF6-EC:DEC:DMC electrolyte, which leads to the deterioration of electrochemical performance of graphite electrode.
2016, 74(10): 839-845
doi: 10.6023/A16060298
Abstract:
Gallium antimonide (GaSb) has a relatively narrow band gap, high electron mobility and excellent saturation velocity, in addition, p-type GaSb nanowires (NWs) can be integrated with n-type nanowire devices potentially. These pro-perties make it applicable both optically and electrically. However, it is noted that the radial dimensions and crystal quality have remarkable influence on the performance of photovoltaic devices. Based on traditional CVD technology, the influence of Au nanoparticles on Vapoure-Liquide-Solid (VLS) growth mechanisms has been studied, GaSb nanowires grown on two different substrates which undergo gold sputtering and gold solution dropping treatment have different geometries of seed particle on nanowire tip and shapes of its body, moreover, the contact angle between these two parts provides stable condition for nanowires growth which has considerable impact on growth direction. The entire growing process is divided into three phases by the temperature: the heating phase, the synthesis phase and the cooling phase. Controllable synthesis has been realized by fixing the synthesis temperature at 900℃ and keeping the other factors unchanged. In the meantime, changing the synthesis time from 60 minutes to 240 minutes in steps, it is found that the breakthrough in radial dimensions and specific surface has been realized with the increase of growing time, the GaSb nanowire of 50 μm has been achieved in this paper. Furthermore, the nanowires were systematically characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD), which suggest that this material has the zincblende structure with good crystal quality and high purity. Also, the Multi-mode phonon oscillation and band-edge emission of the nanowires are shown through Raman spectroscopy (Raman) and Photoluminescence Spectroscopy (PL). All these demonstrate the superior surface morphology and good crystallinity of the obtained nanowires. The study makes contribution to the extensive exploration and novel discoveries of precise controllable growth of GaSb nanowires.
Gallium antimonide (GaSb) has a relatively narrow band gap, high electron mobility and excellent saturation velocity, in addition, p-type GaSb nanowires (NWs) can be integrated with n-type nanowire devices potentially. These pro-perties make it applicable both optically and electrically. However, it is noted that the radial dimensions and crystal quality have remarkable influence on the performance of photovoltaic devices. Based on traditional CVD technology, the influence of Au nanoparticles on Vapoure-Liquide-Solid (VLS) growth mechanisms has been studied, GaSb nanowires grown on two different substrates which undergo gold sputtering and gold solution dropping treatment have different geometries of seed particle on nanowire tip and shapes of its body, moreover, the contact angle between these two parts provides stable condition for nanowires growth which has considerable impact on growth direction. The entire growing process is divided into three phases by the temperature: the heating phase, the synthesis phase and the cooling phase. Controllable synthesis has been realized by fixing the synthesis temperature at 900℃ and keeping the other factors unchanged. In the meantime, changing the synthesis time from 60 minutes to 240 minutes in steps, it is found that the breakthrough in radial dimensions and specific surface has been realized with the increase of growing time, the GaSb nanowire of 50 μm has been achieved in this paper. Furthermore, the nanowires were systematically characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD), which suggest that this material has the zincblende structure with good crystal quality and high purity. Also, the Multi-mode phonon oscillation and band-edge emission of the nanowires are shown through Raman spectroscopy (Raman) and Photoluminescence Spectroscopy (PL). All these demonstrate the superior surface morphology and good crystallinity of the obtained nanowires. The study makes contribution to the extensive exploration and novel discoveries of precise controllable growth of GaSb nanowires.
