Template Assisted Synthesis of Mesoporous Ta₂O₅ Material for Supercapacitor Applications

( Rajesh Rajagopal ),류광선 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

In this work, ordered Ta₂O₅ nanoparticles were synthesized by template assisted hydrothermal process. First, SBA-15 hard template was synthesized by hydrothermal process and it was used as the hard template for the synthesis of Ta₂O₅ nanoparticles. Secondly, Ta₂O₅ nanoparticles were synthesized simple chemical process with controlled pH condition. The crystalline and porous nature of the synthesized material was studied by powder XRD and nitrogen adsorption techniques technique, respectively. The surface morphology of the synthesized Ta₂O₅ nanoparticles was analyzed by FE-SEM analysis. The electrochemical behavior of the synthesized Ta₂O₅ nanoparticles was studied by cyclic voltammetry (CV), charge - discharge (CD) and electrochemical impedance techniques. The specific capacitance values of the synthesized Ta₂O₅ NPs electrode material was calculated from galvanostatic CD technique. The synthesized Ta₂O₅ nanoparticles electrode shows high specific capacitance and energy density value.

Facile hydrothermal synthesis of lanthanum oxide/hydroxide nanoparticles anchored reduced graphene oxide for supercapacitor applications

Rajesh Rajagopal,류광선 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.60 No.-

This paper reports the synthesis of lanthanum oxide/hydroxide nanoparticle (LaNPs)-doped rGO nanosheets. The uniform distribution of LaNPs on the rGO nanosheets was confirmed by FESEM, TEM, and elemental analysis. A dramatic change in electrochemical behavior was observed by adjusting the concentration of LaNPs in rGO (LaG ratio = 1:2, 1:1 and 2:1). The LaG 12 showed a better areal capacitance of 889.29 F cm−2 than LaG 11 (428.58 F cm−2) and LaG 21 (260.72 F cm−2). Further, improved cycle stability (84% after 1000 cycles) with good impedance behavior confirms LaG 12 is a suitable electrode material for high-performance supercapacitor fabrication.

Influence of rare earth elements on porosity controlled synthesis of MnO₂ nanostructures for supercapacitor applications

Rajagopal, Rajesh,Ryu, Kwang-Sun Pergamon Press 2018 Electrochimica Acta Vol. No.

<P><B>Abstract</B></P> <P>Nanostructured MnO<SUB>2</SUB> was synthesized using a facile hydrothermal technique with potassium permanganate as a precursor. Rare earth elements, lanthanum and cerium, were used to control the porosity of the MnO<SUB>2</SUB> nanostructures. Nanorod-, nanoflower-, nanoneedle-, and nanoneedles/nanopetal-shaped MnO<SUB>2</SUB> nanostructures were synthesized by changing the concentration of the rare earth elements. The as-synthesized MnO<SUB>2</SUB> nanorods, La – MnO<SUB>2</SUB> nanoneedles, Ce – MnO<SUB>2</SUB> nanoflowers, and La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals were examined using a range of physico chemical characterization techniques. Scanning electron microscopy and transmission electron microscopy – energy dispersive X-ray spectroscopy confirmed the morphology of the MnO<SUB>2</SUB> nanostructures and the elemental distribution. The porous natures of the synthesized MnO<SUB>2</SUB> nanostructures were analyzed by nitrogen adsorption technique. The electrochemical behavior of the MnO<SUB>2</SUB> nanostructures was examined by cyclic voltammetry, charge – discharge and electrochemical impedance spectroscopy tests. The La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals electrode exhibited a high specific capacitance of 825 F g<SUP>−1</SUP> at an applied current density of 10 A g<SUP>−1</SUP>. The La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals were also mixed with 5, 10, 15 and 20 wt% of rGO nanosheets to enhance the electrochemical behavior. The 20 rGO@La/Ce – MnO<SUB>2</SUB> sample showed extraordinary electrochemical behavior; the calculated specific capacitance was 1165 F g<SUP>−1</SUP> at an applied current density of 10 A g<SUP>−1</SUP>. A 20 rGO@La/Ce – MnO<SUB>2</SUB> and activated carbon asymmetric supercapacitor coin cell device exhibited ∼93% capacitance retention after 1000 cycles. These results highlight the potential of 20 rGO@La/Ce – MnO<SUB>2</SUB> as an electrode material for supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Manganese oxide nanostructures were synthesized by hydrothermal process. </LI> <LI> Lanthanum and cerium used to control the porosity of manganese oxide. </LI> <LI> La/Ce mixed MnO<SUB>2</SUB> nanoneedles/nanopetals showing good electrochemical behavior. </LI> <LI> rGO mixed La/Ce – MnO<SUB>2</SUB> was prepared to improve the storage capacity. </LI> <LI> 20rGO@ La/Ce – MnO<SUB>2</SUB> electrode exhibited high specific capacitance of 1165 F g<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile hydrothermal synthesis of lanthanum oxide/hydroxide nanoparticles anchored reduced graphene oxide for supercapacitor applications

Rajagopal, Rajesh,Ryu, Kwang-Sun THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.60 No.-

<P><B>Abstract</B></P> <P>This paper reports the synthesis of lanthanum oxide/hydroxide nanoparticle (LaNPs)-doped rGO nanosheets. The uniform distribution of LaNPs on the rGO nanosheets was confirmed by FESEM, TEM, and elemental analysis. A dramatic change in electrochemical behavior was observed by adjusting the concentration of LaNPs in rGO (LaG ratio=1:2, 1:1 and 2:1). The LaG 12 showed a better areal capacitance of 889.29Fcm<SUP>−2</SUP> than LaG 11 (428.58Fcm<SUP>−2</SUP>) and LaG 21 (260.72Fcm<SUP>−2</SUP>). Further, improved cycle stability (84% after 1000 cycles) with good impedance behavior confirms LaG 12 is a suitable electrode material for high-performance supercapacitor fabrication.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Synthesis and characterization of complex anion doped Li₇P₂S₈I solid electrolyte for all solid-state lithium battery

( Rajesh Rajagopal ),류광선 한국공업화학회 2023 한국공업화학회 연구논문 초록집 Vol.2023 No.0

Synthesis and electrochemical performance of (100-x)Li7P3S11-xLi3SI composite solid electrolyte for all-solid-state lithium batteries

정수연,Rajesh Rajagopal,류광선 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.95 No.-

Li7P3S11 (LPS) solid electrolytes have great advantages, such as high lithium-ion conductivity, and caneasily fabricate to make bulk-type all-solid-state lithium batteries. However, LPS has a disadvantagebecause of large interfacial resistance with lithium, which give a limitation for all-solid-state battery. Inthis study, (100-x)Li7P3S11-x Li3SI (x = 0. 2 and 5) solid electrolyte composites are prepared by mechanicalball milling process. Various physiochemical analysis was carried out to confirm the proper mixing ofLi7P3S1 and Li3SI solid electrolytes. The addition of Li3SI solid electrolyte, effectively influence the ionicconductivity and electrochemical properties of the Li7P3S1 solid electrolyte. The prepared Li7P3S11/Li3SIsolid electrolyte composites are stable against the lithium metal anode even after 100 h chargedischargingprocess and has stable potential window up to 10 V. In particular, 98Li7P3S11-2Li3SI solidelectrolyte based ASSLBs shows the highest capacity, of 110 mA/g at the current density of 7.5 mA g 1(0.05 C). The charge – discharge cycle stability test also proved the Li3SI mixing to Li7P3S11 helped tomaintain the capacity retention value of100 % after 10 cycles. Therefore, the Li3SI into the Li7P3S11electrolyte helps improve the electrochemical performance.

Study of LiNi0.6Co0.2Mn0.2O2 coated with the Li2ZrO3 nanolayer in all-solid-state lithium ion batteries

김영진,( Rajagopal Rajesh ),류광선 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

LiNi0.6Co0.2Mn0.2O2(NCM) is covered with Li2ZrO3 nanolayer. Li2ZrO3 can block the side reaction of interface between oxide-based cathode and sulfide-based electrolyte due to the higher stability and lower interfatial resistance. Coating of Li2ZrO3 on NCM was obtained by sol-gel technique. NCM and Li and Zr source were dissolved in absolute ethanol separately, and two solution were mixed and evaporated then calcined. Li7P2S11I was used as the solid electrolyte. The structure details of bare and Li2ZrO3-coated NCM were studied by XRD. The morphology of Li2ZrO3-coated NCM and elemental analysis were carried out by SEM and EDS. The thickness of Li2ZrO3 and d-space of Li2ZrO3 and NCM were analyzed by TEM. The electrochemical performances of Li2ZrO3-coated NCM were elucidated from electrochemical impedance spectroscopy, charge-discharge curves, and C-rate performances.

Effects of Zr doping to improve ionic conductivity and lithium-diffusion kinetics of β-LiVOPO4 cathode material

Da-Jeong Park,Rajesh Rajagopal,Kwang-Sun Ryu 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.83 No.-

We tried to improve the ionic conductivity, lithium-ion diffusion, and cycle capacity of pure β-LiVOPO4 cathode material by Zr doping. Pure and Zr-doped β-LiVOPO4 cathode material was synthesized by a lowtemperature sol–gel process. The physiochemical properties of the synthesized materials were analyzed by various characterization techniques. The Zr doping of the β-LiVOPO4 was confirmed by ex situ XANES analysis. The electrochemical behavior of the synthesized material was studied by various electrochemical analyses. The lithium-diffusion coefficient values of pristine and selected Zr-doped βLiVOPO4 cathode materials were studied and compared using SSCV, EIS, and PITT at different voltages. The calculated values of the diffusion coefficients obtained from CV and EIS are in the range of 1014– 1013 cm2 /s. The PITT measurement gives the values of 1012–1011 cm2 /s. Alltechniques indicated that x = 0.03 Zr-doped samples obtained the improved the lithium diffusion coefficient values