S. Amaresh

Adipic acid assisted sol–gel synthesis of Li2MnSiO4 nanoparticles with improved lithium storage properties

An adipic acid assisted sol–gel route was employed to prepare phase pure Li2MnSiO4 under the optimized conditions. Powder X-ray diffraction measurements confirm the formation of orthorhombic Li2MnSiO4 with Pmn21 space group. The oxidation state of Mn(II) was confirmed by electron paramagnetic resonance (EPR) studies. FTIR study was conducted to ensure the formation of a tetrahedral SiO4 group. Morphological features confirmed the appearance of evenly dispersed Li2MnSiO4 spherical nanoparticles with size of ∼30 nm. The Li/Li2MnSiO4 cell was constructed to study the electrochemical performance of Li2MnSiO4 nanoparticles and the cell delivers a stable discharge capacity profile (∼125 mAh g−1) for observed 50 cycles.

Microwave synthesis of graphene/magnetite composite electrode material for symmetric supercapacitor with superior rate performance

Pristine Fe3O4 and Fe3O4–graphene composites were synthesized by using a green and low cost urea-assisted microwave irradiation method and were utilized as electrode materials for symmetric supercapacitor applications. The Fe3O4–graphene symmetric cell exhibited a better electrochemical performance than that of the Fe3O4 cell with enhanced rate performances. The Fe3O4–graphene symmetric cell delivered a stable discharge capacitance, energy and power densities of about 72 F g−1, 9 Wh kg−1 and 3000 W kg−1, respectively at 3.75 A g−1 current density over 100 000 cycles between 0–1 V. The impedance studies also suggested that the Fe3O4–graphene symmetric cell showed lower resistance and high conductivity due to the small particle size, large surface area and good interaction between Fe3O4 particles and graphene layers.

Single-step microwave mediated synthesis of the CoS2 anode material for high rate hybrid supercapacitors

A short time microwave irradiation based synthesis method of phase pure cubic CoS2 nanoparticles is reported in this study for the first time. The energy density (ED) of hybrid supercapacitors based on CoS2 as an anode having activated carbon as a cathode has been enhanced by using the higher operating potential of organic electrolytes and by increasing the concentration of the mobile ionic species at the negative electrode, in addition to the lithium ions present in the electrolyte. The specific capacitance delivered by non-lithiated CoS2 nanoflakes was 52 F g−1 at a current rate of 0.7 A g−1 between 0 and 3 V using a LiPF6-based electrolyte. Increasing the concentration of the mobile ionic species, i.e., lithium, at the anode enhanced the performance of the hybrid supercapacitor to 119 F g−1 at a current rate of 0.7 A g−1. The hierarchical arrangement of pores in the electroactive material allowed high electrolyte access and reduced the length of the ionic pathway. Consequently, the lithiated form exhibited an ED of 37 W h kg−1 with a power density of 1 kW kg−1 at a current rate of 0.7 A g−1, compared to only 15 W h kg−1 for the non-lithiated sample. Furthermore, both samples maintained superior stability over extended cycling for 10000 cycles at a very high PD of 4 kW kg−1 with a capacitance retention of 100% for the lithiated sample and 80% for the non-lithiated sample. These results will be useful in the fabrication of high ED, high rate hybrid supercapacitors for electric vehicle applications.

Fluorine‐Doped Fe2O3 as High Energy Density Electroactive Material for Hybrid Supercapacitor Applications

Nanostructured α-Fe2 O3 with and without fluorine substitution were successfully obtained by a green route, that is, microwave irradiation. The hematite phase materials were evaluated as a high-performance electrode material in a hybrid supercapacitor configuration along with activated carbon (AC). The presence of fluorine was confirmed through X-ray photoelectron spectroscopy and transmission electron microscopy. Fluorine-doped Fe2 O3 (F-Fe2 O3 ) exhibits an enhanced pseudocapacitive performance compared to that of the bare hematite phase. The F-Fe2 O3 /AC cell delivered a specific capacitance of 71 F g(-1) at a current density of 2.25 A g(-1) and retained approximately 90 % of its initial capacitance after 15 000 cycles. Furthermore, the F-Fe2 O3 /AC cell showed a very high energy density of about 28 W h kg(-1) compared to bare hematite phase (∼9 W h kg(-1) ). These data clearly reveal that the electrochemical performance of Fe2 O3 can be improved by fluorine doping, thereby dramatically improving the energy density of the system.

Unveiling organic–inorganic hybrids as a cathode material for high performance lithium-ion capacitors

Novel Li-ion hybrid supercapacitors were developed containing composite cathodes of a conducting polymer – either polyaniline (PANI) or polypyrrole (PPy) – with Li(Mn1/3Ni1/3Fe1/3)O2 nanoparticles. Activated carbon (AC) anodes were used in the presence of an organic electrolyte. Using a PANI composite electrode resulted in a cell with outstanding supercapacitive behavior, even at high currents. It showed better cycleability than the cells using a PPy composite electrode or pristine material. The cell with a PANI composite electrode delivered high specific capacitances of 140, 93, and 56 F g−1 at current densities of 0.72, 1.45 and 2.15 A g−1, respectively. The observed capacitances are the best yet reported for hybrid supercapacitors based on Li-intercalating materials in organic electrolytes. The hybrid supercapacitor containing PANI delivered maximum energy and power densities of 49 W h kg−1 and 3 kW kg−1, respectively. These results demonstrate the potential of developing polymer-encapsulated, Li-intercalating materials for high-performance, Li-ion, hybrid supercapacitors.

Microwave assisted green synthesis of MgO-carbon nanotube composites as electrode material for high power and energy density supercapacitors†

In the present study, a novel attempt has been made to fabricate an asymmetric supercapacitor based on a MgO–multi-walled carbon nanotube (MWCNT) composite as the cathode and activated carbon (AC) as the anode using an organic electrolyte (1 M LiPF6 in EC : DMC 1 : 1 by volume). Supercapacitance behavior is examined by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge studies. The results reveal that the test cell displayed excellent capacitance performance between 0 and 3 V. The MgO–MWCNT/AC cell delivers a specific capacitance of 66 F g−1 at a current density of 2.2 A g−1. Cycling studies show that this cell can retain 97% of its initial capacitance after 35 000 cycles. Additionally, the MgO–MWCNT/AC cell also exhibits a maximum energy density of 30 W h kg−1, which is comparable to the values obtained from other supercapacitor configurations. These results encourage utilization of the MgO–MWCNT composite as a potential electrode in developing green and low cost energy storage devices with high energy and power densities as well as prolonged cycle life.

Effect of carbon coating on the electrochemical properties of Co2SnO4 for negative electrodes in Li-ion batteries

Co2SnO4 particles were synthesized by a sonochemical method under different pH conditions, followed by carbon coating by a hydrothermal method. The thermal stability and compound formation temperature were identified through thermogravimetric analysis (TGA). The X-ray diffraction (XRD) pattern elucidated the compound formation of Co2SnO4 with cubic structure. Co2SnO4 encapsulated with carbon was confirmed through the TEM and HRTEM analysis and the approximate thickness of carbon was around 20 nm. The pristine-Co2SnO4 and carbon coated Co2SnO4 provided a discharge capacity of 777 mA h g−1 and 780 mA h g−1 at the current density of 40 mA g−1 with the capacity retention of 67% and 81% respectively in the 20th cycle. The charge transfer resistance of carbon coated Co2SnO4 was low when compared to pristine Co2SnO4 which lead to good reversibility of the material. The electrochemical study revealed the excellent electrochemical performance of the carbon coated Co2SnO4 particles with superior cycling stability and electronic conductivity.

High‐Power Lithium‐Ion Capacitor using LiMnBO3‐Nanobead Anode and Polyaniline‐Nanofiber Cathode with Excellent Cycle Life

LiMnBO3 nanobeads (LMB-NB) with uniform size and distribution were synthesized using a urea-assisted microwave/solvothermal method. The potential application of LMB-NBs as an anode for a lithium-ion hybrid capacitor (Li-AHC) was tested with a polyaniline-nanofiber (PANI-NF) cathode in a nonaqueous LiPF6 (1 M)-ethylene carbonate/dimethyl carbonate electrolyte. Cyclic voltammetry (CV) and charge-discharge (C/DC) studies revealed that the PANI-NF/LMB-NB cell showed an exceptional capacitance behavior between 0-3 V along with a prolonged cycle life. A discharge capacitance of about 125 F g(-1) , and energy and power densities of about 42 Wh kg(-1) and 1500 W kg(-1) , respectively, could be obtained at a current density of 1 A g(-1) ; those Li-AHC values are higher relative to cells containing various lithium intercalation materials in nonaqueous electrolytes. In addition, the PANI-NF/LMB-NB cell also had an outstanding rate performance with a capacitance of 54 F g(-1) and a power density of 3250 W kg(-1) at a current density of 2.25 A g(-1) and maintained 94% of its initial value after 30000 cycles. This improved capacitive performance with an excellent electrochemical stability could be the result of the morphological features and inherent conductive nature of the electroactive species.

Alumina coating on 5 V lithium cobalt fluorophosphate cathode material for lithium secondary batteries – synthesis and electrochemical properties

The high voltage cathode material, Li2CoPO4F was successfully synthesized and coated with various amounts of Al2O3 for enhanced electrochemical performance. X-ray diffraction data revealed that the unit cell had an orthorhombic structure with the Pnma space group. An initial discharge capacity of ∼127 mA h g−1 was obtained between 2 and 5.1 V. The capacity retention, ratio of discharge capacity at the 15th cycle to that at the 1st cycle, at a current rate of C/2 was increased from 53% for the pristine sample to 73% for 1 wt% Al2O3 coated Li2CoPO4F. Cyclic voltammetry and charge–discharge studies showed an increased operating voltage for Li2CoPO4F after Al2O3 coating. Electrochemical impedance spectroscopy results suggested a reduction in charge transfer resistance in the as-prepared samples. Moreover, the reduction in irreversible capacity loss, defined as the difference between charge capacity and discharge capacity of the same cycle, in the initial cycle suggested a decrease in electrolyte oxidation after the coating process. A uniform amorphous layer of Al2O3 coating of ∼3 nm thickness protected the surface of Li2CoPO4F during high voltage operation.

Reply to the ‘Comment on “Microwave synthesis of graphene/magnetite composite electrode material for symmetric supercapacitor with superior rate performance”’ by Rajaperumal M., RSC Adv., 2017, 7, DOI: 10.1039/c7ra04129b

First of all, this work was completed at the Chonnam National University, Korea by the rst author of this paper Mr Karthikeyan. (1) The main scope of our work is to facilitate the synthesis of Fe3O4–graphene (Fe–GNS) nanoparticles using a simple and green synthesis method and to study the effect of the preparation technique on their capacitive performance. Since the preparation conditions affect the electrochemical performance of any cathode materials (Fe3O4-conductive carbon composites have already been prepared using various methods), a novel microwave method was adopted to fabricate the Fe–GNS composites and their application as capacitors studied. In our work, we have achieved excellent capacitive performance of the Fe–GNS system, which was attributed to its morphological features (explained well in the manuscript itself). (2) Regarding the weight, the weight of the active material in the electrode was 0.3125 mg. The weight difference was about 0.4 mg and the active material in the electrode was about 0.3125 ( 79 wt%). (3) With reference to the article published in J. Mater. Chem., 2011, 21, 3422–3427, they have achieved 480 F g 1 at 5 A g 1 as shown in Fig. 3b. As you can see from Fig. 3b, the discharge time could be 43 s, voltage is 1 V and current is 5 A g 1 and the authors reported the capacitance of 480 F g . (4) About your question on capacitive performance, the rate performance of the Fe–GNS was resulted from its morphological feature as explained well in the paper. Since the open system formed during the synthesis of Fe–GNS can accommodate more electrolyte within the composite structure, providing a exible structure against inherent mechanical stresses formed during the charge discharge at