Books by Aravindaraj G Kannan
Papers by Aravindaraj G Kannan
The critical issues that hinder the practical applications of lithium−sulfur batteries, such as d... more The critical issues that hinder the practical applications of lithium−sulfur batteries, such as dissolution and migration of lithium polysulfides, poor electronic conductivity of sulfur and its discharge products, and low loading of sulfur, have been addressed by designing a functional separator modified using hydroxyl-functionalized carbon nanotubes (CNTOH). Density functional theory calculations and experimental results demonstrate that the hydroxyl groups in the CNTOH provoked strong interaction with lithium polysulfides and resulted in effective trapping of lithium polysulfides within the sulfur cathode side. The reduction in migration of lithium polysulfides to the lithium anode resulted in enhanced stability of the lithium electrode. The conductive nature of CNTOH also aided to efficiently reutilize the adsorbed reaction intermediates for subsequent cycling. As a result, the lithium−sulfur cell assembled with a functional separator exhibited a high initial discharge capacity of 1056 mAh g −1 (corresponding to an areal capacity of 3.2 mAh cm −2) with a capacity fading rate of 0.11% per cycle over 400 cycles at 0.5 C rate.
Nitrogen and sulfur co-doped, hierarchically porous graphene is synthesized. EDLC with co-doped g... more Nitrogen and sulfur co-doped, hierarchically porous graphene is synthesized. EDLC with co-doped graphene exhibits high capacitance and good cycling stability. Good performance is attributed to co-doping and hierarchical porous structures. a b s t r a c t Hierarchically porous graphene nanosheets co-doped with nitrogen and sulfur are synthesized via a simple hydrothermal method, followed by a pore activation step. Pore architectures are controlled by varying the ratio of chemical activation agents to graphene, and its influence on the capacitive performance is evaluated. The electric double layer capacitor (EDLC) assembled with optimized dual-doped graphene delivers a high specific capacitance of 146.6 F g À1 at a current density of 0.8 A g À1 , which is higher than that of cells with un-doped and single-heteroatom doped graphene. The EDLC with dual-doped graphene electrodes exhibits stable cycling performance with a capacitance retention of 94.5% after 25,000 cycles at a current density of 3.2 A g À1. Such a good performance can be attributed to synergistic effects due to co-doping of the graphene nanosheets and the presence of hierarchical porous structures.
Hierarchal porous carbon is obtained from waste watermelon rind.
Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely us... more Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO 2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO 2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO 2 nanoparticles was remarkably improved at elevated temperatures. The rapidly expanding use of rechargeable lithium-ion batteries as power sources for portable electronic devices, electric vehicles and energy storage systems has led to intensive research on electrolyte systems with high elec-trochemical performance 1–8. The liquid electrolyte used in lithium-ion batteries is based on lithium salt dissolved in a mixture of organic carbonate solvents. It provides high conductivity, acceptable electrochemical stability and good cycle performance. However, current lithium-ion batteries have risks associated with leakage and fire hazards due to the high flammability of the organic solvents 9–11. In addition, the polyolefin separators used in lithium-ion batteries may shrink and even melt at elevated temperatures, which may cause a short circuit between the two electrodes in cases where unusually high heat is generated 12–14. Therefore, there is a pressing need for safer and more reliable electrolyte systems. Among various electrolyte systems, gel polymer electrolytes have received considerable attention due to their high ionic conductivity, good interfacial adhesion to electrodes and effective encapsulation of organic solvents in the cell, resulting in suppression of solvent leakage and enhanced safety 15–17. However, the incorporation of liquid electrolyte into the polymer matrix to improve the ionic conductivity deteriorated the mechanical strength of the polymer electrolyte, leading to internal shorts and battery failure. The mechanical strength of the gel polymer electrolytes was enhanced by in-situ chemical cross-linking or addition of inorganic fillers such as SiO 2 , Al 2 O 3 , TiO 2 and BaTiO 3 18–26. In the in-situ thermal cross-linking process, gel electrolyte precursors containing liquid electrolyte and cross-linking agents were injected directly into the cell, and a cross-linked gel polymer electrolyte was formed by free radical polymerization triggered by thermal initiation 27–29. The cross-linked polymer networks that were swelled with the liquid electrolyte showed high ionic conductivity, favorable interfacial properties and good mechanical strength. In our previous studies, we synthesized cross-linked composite polymer electrolytes using reactive SiO 2 particles with C= C double bonds 30 .
Silicon alloys composed of silicon nanoparticles embedded in inert Cu-Al-Fe matrix phases were sy... more Silicon alloys composed of silicon nanoparticles embedded in inert Cu-Al-Fe matrix phases were synthesized and encapsulated with reduced graphene oxide (rGO) nanosheets. Successful synthesis of the silicon alloys and their encapsulation with rGO were confirmed by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopic analyses. The silicon alloy encapsulated with an optimal amount of rGO delivered an initial discharge capacity of 1140.7 mAh g À1 with good capacity retention and exhibited excellent rate capability. This superior performance could be attributed to the unique structure of silicon alloy encapsulated by rGO, which could effectively accommodate the large volume change during cycling and provide continuous electronic conduction pathway in the electrode.
The development of silicon-based anodes with high capacity and good cycling stability for next-ge... more The development of silicon-based anodes with high capacity and good cycling stability for next-generation lithium-ion batteries is a very challenging task due to the large volume changes in the electrodes during repeated cycling, which results in capacity fading. In this work, we synthesized silicon alloy as an active anode material, which was composed of silicon nanoparticles embedded in Cu−Al−Fe matrix phases. Poly(amide imide)s, (PAI)s, with different thermal treatments were used as polymer binders in the silicon alloy-based electrodes. A systematic study demonstrated that the thermal treatment of the silicon alloy electrodes at high temperature made the electrodes mechanically strong and remarkably enhanced the cycling stability compared to electrodes without thermal treatment. The silicon alloy electrode thermally treated at 400 °C initially delivered a discharge capacity of 1084 mAh g −1 with good capacity retention and high Coulombic efficiency. This superior cycling performance was attributed to the strong adhesion of the PAI binder resulting from enhanced secondary interactions, which maintained good electrical contacts between the active materials, electronic conductors, and current collector during cycling. These findings are supported by results from X-ray photoelectron spectroscopy, scanning electron microscopy, and a surface and interfacial cutting analysis system.
The growth of silicon nanoparticles on a graphene surface without forming the unwanted silicon ca... more The growth of silicon nanoparticles on a graphene surface without forming the unwanted silicon carbide (SiC) phase has been challenging. Herein, the critical issues surrounding silicon anode materials for lithium-ion batteries, such as electrode pulverization, unstable solid electrolyte interphase and low electrical conductivity, have been addressed by growing silicon nanoparticles smaller than 10 nm, covalently bonded to a reduced graphene oxide (rGO) surface. The successful growth of SiC-free silicon nanoparticles covalently attached to the rGO surface was confirmed by using various spectroscopic and microscopic analyses. The rGO–Si delivered an initial discharge capacity of 1338.1 mA h g À1 with capacity retention of 87.1% after the 100th cycle at a current rate of 2100 mA g À1 , and exhibited good rate capability. Such enhanced electrochemical performance is attributed to the synergistic effects of combining ultra-small silicon nanoparticles and rGO nanosheets. Here, rGO provides a continuous electron conducting network, whereas, ultra-small silicon particles reduce ionic diffusion path length and accommodate higher stress during volume expansion upon lithiation.
Trapping lithium polysulfides formed in the sulfur positive electrode of lithium−sulfur batteries... more Trapping lithium polysulfides formed in the sulfur positive electrode of lithium−sulfur batteries is one of the promising approaches to overcome the issues related to polysulfide dissolution. In this work, we demonstrate that intrinsically hydrophilic magnesium oxide (MgO) nanoparticles having surface hydroxyl groups can be used as effective additives to trap lithium polysulfides in the positive electrode. MgO nanoparticles were uniformly distributed on the surface of the active sulfur, and the addition of MgO into the sulfur electrode resulted in an increase in capacity retention of the lithium−sulfur cell compared to a cell with pristine sulfur electrode. The improvement in cycling stability was attributed to the strong chemical interactions between MgO and lithium polysulfide species, which suppressed the shuttling effect of lithium polysulfides and enhanced the utilization of the sulfur active material. To the best of our knowledge, this report is the first demonstration of MgO as an effective functional additive to trap lithium polysulfides in lithium−sulfur cells.
ACS applied materials & interfaces, Jan 28, 2015
The enhanced stability of lithium metal is vital to the development of high energy density lithiu... more The enhanced stability of lithium metal is vital to the development of high energy density lithium batteries due to its higher specific capacity and low redox potential. Herein, we demonstrate that nitrogen and sulfur codoped graphene (NSG) nanosheets coated on a polyethylene separator stabilized the lithium electrode in lithium metal batteries by effectively suppressing dendrite growth and maintaining a uniform ionic flux on the metal surface. The ultrathin layer of NSG nanosheets also improved the dimensional stability of the polymer separator at elevated temperatures. In addition, the enhanced interfacial interaction between the NSG-coated separator and lithium metal via electrostatic attraction released the surface tension of lithium metal and suppressed the initiation of dendrite growth on lithium metal. As a result, the electrochemical performance of a lithium metal cell composed of a LiNi0.8Co0.15Al0.05O2 positive electrode with an NSG-coated separator was remarkably improved...
Smart Materials V, 2008
Here we describe a new class of near superhydrophobic surfaces formed using fluorinated polyhedra... more Here we describe a new class of near superhydrophobic surfaces formed using fluorinated polyhedral oligosilsesquioxane (FluoroPOSS) urethane hybrids and porous silicon gradients (pSi). We demonstrate that the surface segregation behavior of the hydrophobic fluoro component can be controlled by the type and nature of chain extender of the urethane and resultant hydrophobic association via intra or intermolecular aggregation. The surface film formed exhibits near superhydrophobicity. This work has significant potential for applications in antifouling and self-cleaning coatings, biomedical devices, microfluidic systems and tribological surfaces.
Mesoporous carbon on nitrogen and sulfur co-doped graphene nanosheets (NSGC) was synthesized and ... more Mesoporous carbon on nitrogen and sulfur co-doped graphene nanosheets (NSGC) was synthesized and its bi-functional catalytic activity toward oxygen reduction reaction and oxygen evolution reaction was investigated. The NSGC material showed high bi-functional catalytic activity due to the synergistic effect of co-doping of sulfur and nitrogen, as well as the presence of a hierarchical porous structure. The enhanced bi-functional catalytic activity of NSGC facilitated the efficient formation and decomposition of Li2O2 on the air cathode. The lithium–oxygen cell assembled with the NSGC-based air cathode delivered a high initial discharge capacity of 11[thin space (1/6-em)]431 mA h g−1 and exhibited good cycling stability. The hybrid structure consisting of mesoporous carbon with co-doped graphene nanosheets can be an effective strategy to improve the round-trip efficiency and cycle life of lithium–oxygen batteries.
We demonstrate the effectiveness of dual-layer coating of cathode active materials for improving ... more We demonstrate the effectiveness of dual-layer coating of cathode active materials for improving the cycling performance and thermal stability of lithium-ion cells. Layered nickel-rich Li-Ni 0.6 Co 0.2 Mn 0.2 O 2 cathode material was synthesized and double-layer coated with alumina nanoparticles and poly(3,4-ethylenedioxythiophene)co-poly(ethylene glycol). The lithium-ion cells assembled with a graphite negative electrode and a double-layer-coated LiNi 0.6 Co 0.2 Mn 0.2 O 2 positive electrode exhibited high discharge capacity, good cycling stability, and improved rate capability. The protective double layer formed on the surface of LiNi 0.6 Co 0.2 Mn 0.2 O 2 materials effectively inhibited the dissolution of Ni, Co, and Mn metals from cathode active materials and improved thermal stability by suppressing direct contact between electrolyte solution and delithiated Li 1−x Ni 0.6 Co 0.2 Mn 0.2 O 2 materials. This effective design strategy can be adopted to enhance the cycling performance and thermal stability of other layered nickel-rich cathode materials used in lithium-ion batteries.
Photoelectrochemical cells (PECs) with a structure of F-doped SnO2 (FTO)/graphene oxide (GO)/hema... more Photoelectrochemical cells (PECs) with a structure of F-doped SnO2 (FTO)/graphene oxide (GO)/hematite (α-Fe2O3) photoanode were fabricated, in which GO serves as a sacrificial underlayer. In contrast to low-temperature sintering carried out under a normal atmosphere, high-temperature sintering was carried out for the GO underlayer-based hematite photoanodes. The photocurrent density of the PECs with GO underlayers gradually increased as the spin speed of the FTO substrate increased. In particular, GO at a spin speed of 5000 rpm showed the highest photocurrent of 1.3 mA/cm2. The higher performance of the GO/α-Fe2O3 photoanodes was attributed to the improved FTO/α-Fe2O3 interface. When sintered at 800 °C for activation of the hematite (FTO/GO/α-Fe2O3) photoanodes, the GO layers before being decomposed act as localized hot zones at the FTO/α-Fe2O3 interface. These localized hot zones play a very crucial role in reducing the microstrain (increased crystallinity) which was confirmed from the synchrotron X-ray diffraction studies. The sacrificial GO underlayer may contribute to relaxing the inhomogeneous internal strain of the α-Fe2O3 nanorods and reducing the deformation of FTO to an extent. In other words, the reduction of the microstrain minimizes the lattice imperfections and defects at the FTO/α-Fe2O3 interface, which may enhance the charge collection efficiency, as demonstrated by the impedance measurements. From the EXAFS analysis, it is clearly evident that the sacrificial GO underlayer does not affect the structure of α-Fe2O3 in the short range. The effects of the GO sacrificial layers are restricted to the FTO/α-Fe2O3 interface, and they do not affect the bulk properties of α-Fe2O3.
A highly efficient nitrogen and sulfur co-doped graphene (NSG) nanosheet for dye-sensitized solar... more A highly efficient nitrogen and sulfur co-doped graphene (NSG) nanosheet for dye-sensitized solar cells (DSSCs) was synthesized using a simple hydrothermal method, and its electrocatalytic activity towards the I 3 À /I À redox reaction was investigated. The NSG materials showed a uniform distribution of nitrogen and sulfur heteroatoms throughout the graphene nanosheet. The doped nitrogen was present in the form of pyridinic, pyrrolic and graphitic states, and the doped sulfur was present in the C-S-C configuration. The DSSC with the NSG counter electrode exhibited a high conversion efficiency (7.42%), similar to that of the Pt counter electrode (7.56%) and much higher than that of the only N-or S-doped graphene electrodes. The high catalytic activity of the NSG electrode is attributed to the synergistic effect of the high charge polarization arising from the difference in electronegativity between nitrogen and carbon as well as the structural distortion caused by the bigger atomic size of the sulfur atom. To the best of our knowledge, the synergistic effect of co-doping of graphene on the counter electrode performance in DSSCs is demonstrated for the first time, and co-doping is proposed as a promising approach to enhance the photovoltaic performance of DSSCs. Korea † Electronic supplementary information (ESI) available: TEM images of NG and SG control samples; XPS survey spectra of NG, SG, NSG and GO nanosheets; FT-IR spectrum of the NSG sample; XRD patterns of graphite, GO and NSG samples; photocurrent density-voltage curves of DSSCs with NSG counter electrodes of different thicknesses; CVs of NSG, SG, NG and rGO samples. See
Hydrogen bond rich segmented poly(urethane-urea) was synthesized from methylene diphenylisocyanat... more Hydrogen bond rich segmented poly(urethane-urea) was synthesized from methylene diphenylisocyanate (MDI) and three generations of polyurea-malonamide dendrons as hard segment and polycaprolactone diol as soft segment for thin film applications. The prepared polymers were characterized using spectroscopic, microscopic and thermal analyses. The formation of urethane linkage during the prepolymer reaction and the urea linkage between prepolymer and the dendrons is confirmed by Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (NMR) spectroscopy. FTIR shows the presence of hydrogen bonding of –NH groups with both urethane carbonyl group from hard segment and the ether group from the soft segment. However, the phase mixing of hard and soft segments decreases with the higher generation dendrons, as evidenced from FTIR. This observation was confirmed by phase images of the atomic force microscopy (AFM). The coating when applied to clean steel substrates via dip coating reveals uniform, dense and essentially defect free morphology. The work demonstrates that the mechanical properties of the hybrid thin films are dependent on the generation of the dendrons and provides a platform for surface engineering with tunable elastic modulus.
Journal of materials chemistry A
The application of lithium ion batteries in high power applications such as hybrid electric vehic... more The application of lithium ion batteries in high power applications such as hybrid electric vehicles and electric grid systems critically requires drastic improvement in the electronic conductivity using effective materials design and strategies. Here, we demonstrate that the growth of a multi-component structure of composition LiTi 2 (PO 4 ) 3 [LTP] on a reduced graphene oxide (rGO) surface via a facile synthetic strategy could achieve an ultrahigh rate capability with the total carbon content as low as 1.79 wt%.
Journal of power sources
The slow kinetics of bigger-sized sodium ions in intercalation compounds restricts the practical ... more The slow kinetics of bigger-sized sodium ions in intercalation compounds restricts the practical applications of sodium batteries. In this work, sodium ion intercalation/de-intercalation behavior of Na0.44MnO2 (NMO), which is one of the promising cathode materials for sodium batteries, is presented in both aqueous and non-aqueous electrolyte systems. The NMO samples synthesized using modified Pechini method shows better rate capability in 0.5 M sodium sulfate aqueous electrolyte system than the 1 M sodium perchlorate non-aqueous system. The difference in the rate performance is extensively investigated using electrochemical impedance spectroscopy (EIS) measurements and the apparent diffusion coefficients of sodium in NMO are determined to be in the range of 1.08 × 10−13 to 9.15 × 10−12 cm2 s−1 in aqueous system and in the range of 5.75 × 10−16 to 2.14 × 10−14 cm2 s−1 in non-aqueous systems. The differences in the evaluated rate capability are mainly attributed to nearly two to three orders of magnitude difference in the apparent diffusion coefficient along with the charge transfer resistance and the resistance from the formed SEI layer.► Na0.44MnO2 particles were synthesized by a modified Pechini method. ► Kinetics behavior of sodium ions analyzed in aqueous and non-aqueous electrolytes. ► Better rate capability in aqueous system due to higher apparent diffusion coefficient. ► Also attributed to lower charge transfer resistance and no SEI layer formation.
ACS nano, Jan 1, 2012
Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphol... more Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UVÀvis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP
Carbon, Jan 1, 2011
Consolidated carbonaceous samples prepared by spark plasma sintering of multi-walled carbon nanot... more Consolidated carbonaceous samples prepared by spark plasma sintering of multi-walled carbon nanotubes are analyzed, and the effect of the heating regime on their morphology, density, thermal stability, electron field emission and adhesive behavior studied. The trend in the field emission properties of these samples is explained by the changes in the mobility of the nanotube tips. The effect of such changes in the number of free nanotube tips is also deduced from micro-adhesion data, obtained from pull-off tests using atomic force microscopy.
Uploads
Books by Aravindaraj G Kannan
Papers by Aravindaraj G Kannan