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Karthikeyan, Kaliyappan,Amaresh, Samuthirapandian,Son, Ju-Nam,Kim, Shin-Ho,Kim, Min-Chul,Kim, Kwang-Jin,Lee, Sol-Nip,Lee, Yun-Sung Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.1
Layered $Li_{1+x}(Mn_{0.4}Ni_{0.4}Fe_{0.2})_{1-x}O_2$ (0 < x < 0.3) solid solutions were synthesized using solgel method with adipic acid as chelating agent. Structural and electrochemical properties of the prepared powders were examined by means of X-ray diffraction, Scanning electron microscopy and galvanostatic charge/discharge cycling. All powders had a phase-pure layered structure with $R\bar{3}m$ space group. The morphological studies confirmed that the size of the particles increased at higher x content. The charge-discharge profiles of the solid solution against lithium using 1 M $LiPF_6$ in EC/DMC as electrolyte revealed that the discharge capacity increases with increasing lithium content at the 3a sites. Among the cells, $Li_{1.2}(Mn_{0.32}Ni_{0.32}Fe_{0.16})O_2$ (x = 0.2)/$Li^+$ exhibits a good electrochemical property with maximum initial capacity of 160 $mAhg^{-1}$ between 2-4.5 V at 0.1 $mAcm^{-2}$ current density and the capacity retention after 25 cycles was 92%. Whereas, the cell fabricated with x = 0.3 sample showed continuous capacity fading due to the formation of spinel like structure during the subsequent cycling. The preparation of solid solutions based on $LiNiO_2-LiFeO_2-Li_2MnO_3$ has improved the properties of its end members.
Kaliyappan Karthikeyan,Samuthirapandian Amaresh,Ju-Nam Son,Shin-Ho Kim,Min-Chul Kim,김광진,이윤성,Sol-Nip Lee 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.1
Layered Li1+x(Mn0.4Ni0.4Fe0.2)1-xO2 (0 < x < 0.3) solid solutions were synthesized using solgel method with adipic acid as chelating agent. Structural and electrochemical properties of the prepared powders were examined by means of X-ray diffraction, Scanning electron microscopy and galvanostatic charge/discharge cycling. All powders had a phase-pure layered structure with R3m space group. The morphological studies confirmed that the size of the particles increased at higher x content. The charge-discharge profiles of the solid solution against lithium using 1 M LiPF6 in EC/DMC as electrolyte revealed that the discharge capacity increases with increasing lithium content at the 3a sites. Among the cells, Li1.2(Mn0.32Ni0.32Fe0.16)O2 (x = 0.2)/ Li+ exhibits a good electrochemical property with maximum initial capacity of 160 mAhg−1 between 2-4.5 V at 0.1 mAcm−2 current density and the capacity retention after 25 cycles was 92%. Whereas, the cell fabricated with x = 0.3 sample showed continuous capacity fading due to the formation of spinel like structure during the subsequent cycling. The preparation of solid solutions based on LiNiO2-LiFeO2-Li2MnO3 has improved the properties of its end members.
Karthikeyan, Kaliyappan,Amaresh, Samuthirapandian,Lee, Sol Nip,Aravindan, Vanchiappan,Lee, Yun Sung Wiley-VCH 2014 Chemistry - An Asian Journal Vol.9 No.3
<P>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.</P>
Karthikeyan, Kaliyappan,Amaresh, Samuthirapandian,Lee, Sol-Nip,An, Jae-Yeon,Lee, Yun-Sung Wiley-VCH 2014 ChemSusChem Vol.7 No.8
<P>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.</P>
Karthikeyan, Kaliyappan,Amaresh, Samuthirapandiyan,Lee, Sol Nip,Sun, Xueliang,Aravindan, Vanchiappan,Lee, Young-Gi,Lee, Yun Sung Wiley-VCH 2014 ChemSusChem Vol.7 No.5
<P>Very high surface area activated carbons (AC) are synthesized from pine cone petals by a chemical activation process and subsequently evaluated as an electrode material for supercapacitor applications in a nonaqueous medium. The maximum specific surface area of 3950?m(2) ?g(-1) is noted for the material treated with a 1:5 ratio of KOH to pine cone petals (PCC5), which is much higher than that reported for carbonaceous materials derived from various other biomass precursors. A symmetric supercapacitor is fabricated with PCC5 electrodes, and the results showed enhanced supercapacitive behavior with the highest energy density of 61?Wh?kg(-1). Furthermore, outstanding cycling ability is evidenced for such a configuration, and 90?% of the initial specific capacitance after 20,000?cycles under harsh conditions was observed. This result revealed that the pine-cone-derived high-surface-area AC can be used effectively as a promising electrode material to construct high-energy-density supercapacitors.</P>