Browsing by Author "Leonid, Vasylechko"

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IMPROVED ELECTROCHEMICAL PERFORMANCES OF LIMNPO4 SYNTHESIZED BY A HYDROTHERMAL METHOD FOR LI-ION SUPERCAPATTERIES
(Springer, 2018-09-10) Natarjan, Priyadharsini; Amirthalingam, Shanmugavani; Subramani, Surendran; Baskar, Senthilkumar; Leonid, Vasylechko; Ramakrishnan, Kalai Selvan
Developing high-performance positrode materials are essential to attain high energy supercapatteries. In this regard, the electrochemical performances of the hydrothermally synthesized LiMnPO4 are studied. The crystal structures of the materials are elucidated using Full-profile XRD Rietveld refinement. The LiMnPO4 particles showed uniform elongated spherical shape with rice-like morphology. The rice-like LiMnPO4 showed a higher specific capacity of 492 C g−1 at 2 mV s−1 than highly agglomerated particles synthesized through sol–gel thermolysis method (191 C g−1) in 1 M LiOH aqueous electrolyte. The supercapattery is fabricated with rice-like LiMnPO4 and activated carbon (AC) as positrode and negatrode, respectively. The supercapattery (AC||LMP-H) delivered a higher capacitance around 99 F g−1 along with an improved energy density of 31 Wh kg−1. On the other hand, the LiMnPO4 prepared by sol–gel thermolysis method exhibited a very low capacitance of 35 F g−1 at 0.6 mA for the fabricated device (AC||LMP-S) with the lesser energy density about 11 Wh Kg−1 at a power density of 198 W kg−1. The reason behind the improved performance is explained based on the crystal structure as well as lower charge transfer resistance.
IMPROVED ELECTROCHEMICAL PERFORMANCES OF LIMNPO4 SYNTHESIZED BY A HYDROTHERMAL METHOD FOR LI-ION SUPERCAPATTERIES
(Springer Link, 2018-09-10) Natarjan, Priyadharsini; Amirthalingam, Shanmugavani; Subramani, Surendran; Baskar, Senthilkumar; Leonid, Vasylechko; Ramakrishnan, Kalai Selvan
Developing high-performance positrode materials are essential to attain high energy supercapatteries. In this regard, the electrochemical performances of the hydrothermally synthesized LiMnPO4 are studied. The crystal structures of the materials are elucidated using Full-profile XRD Rietveld refinement. The LiMnPO4 particles showed uniform elongated spherical shape with rice-like morphology. The rice-like LiMnPO4 showed a higher specific capacity of 492 C g−1 at 2 mV s−1 than highly agglomerated particles synthesized through sol–gel thermolysis method (191 C g−1) in 1 M LiOH aqueous electrolyte. The supercapattery is fabricated with rice-like LiMnPO4 and activated carbon (AC) as positrode and negatrode, respectively. The supercapattery (AC||LMP-H) delivered a higher capacitance around 99 F g−1 along with an improved energy density of 31 Wh kg−1. On the other hand, the LiMnPO4 prepared by sol–gel thermolysis method exhibited a very low capacitance of 35 F g−1 at 0.6 mA for the fabricated device (AC||LMP-S) with the lesser energy density about 11 Wh Kg−1 at a power density of 198 W kg−1. The reason behind the improved performance is explained based on the crystal structure as well as lower charge transfer resistance.
SOL-GEL SYNTHESIS, STRUCTURAL REFINEMENT, AND ELECTROCHEMICAL PROPERTIES OF POTASSIUM MANGANESE PHOSPHATE FOR SUPERCAPACITORS
(Springer Link, 2018-01-26) Priyadharsini, N; Shanmugavani, A; Leonid, Vasylechko; Kalai Selvan, R
Using sol-gel thermolysis method, potassium manganese phosphate (a mixture of KMnPO4⋅H2O and KMnPO4 phases) was synthesized for supercapacitor applications. XRD analysis revealed phase composition and crystal structure of the prepared material. The dittmarite-type structure of KMnPO4⋅H2O as the primary phase was identified through full profile Rietveld refinement technique. The possible four normal modes of vibrations ν1(A1), ν2(E), ν3(F2), and ν4(F2) were analyzed through FTIR spectrum. Submicron-sized particles are identified using FE-SEM and TEM images. The layered structure of potassium manganese phosphate was corroborated through SAED pattern. Electrochemical performances of the mixed potassium manganese phosphate are investigated using cyclic voltammetry (CV) to identify the suitable aqueous electrolytes (1 M KOH, 1 M LiOH, and 1 M NaOH). It provides the maximum specific capacitance of 516 F g−1 at 2 mV s−1 in 1 M KOH aqueous electrolyte. The Trasatti plot revealed that the observed high specific capacitance mainly arises from the inner surface charge contribution. The electrode shows the better specific capacity of 329 F g−1 at a current density of 0.6 mA cm−2 in galvanostatic charge-discharge measurements. The electrochemical impedance spectral analysis (EIS) further corroborates that the charge-transfer resistance (Rct) is low in 1 M KOH (2.25 Ω) electrolyte than in 1 M LiOH (9.2 Ω) and 1 M NaOH (50.7 Ω) electrolytes.
SOL-GEL SYNTHESIS, STRUCTURAL REFINEMENT, AND ELECTROCHEMICAL PROPERTIES OF POTASSIUM MANGANESE PHOSPHATE FOR SUPERCAPACITORS
(Springer, 2018-01-26) N, Priyadharsini; A, Shanmugavani; Leonid, Vasylechko; R, Kalai Selvan
Using sol-gel thermolysis method, potassium manganese phosphate (a mixture of KMnPO4⋅H2O and KMnPO4 phases) was synthesized for supercapacitor applications. XRD analysis revealed phase composition and crystal structure of the prepared material. The dittmarite-type structure of KMnPO4⋅H2O as the primary phase was identified through full profile Rietveld refinement technique. The possible four normal modes of vibrations ν1(A1), ν2(E), ν3(F2), and ν4(F2) were analyzed through FTIR spectrum. Submicron-sized particles are identified using FE-SEM and TEM images. The layered structure of potassium manganese phosphate was corroborated through SAED pattern. Electrochemical performances of the mixed potassium manganese phosphate are investigated using cyclic voltammetry (CV) to identify the suitable aqueous electrolytes (1 M KOH, 1 M LiOH, and 1 M NaOH). It provides the maximum specific capacitance of 516 F g−1 at 2 mV s−1 in 1 M KOH aqueous electrolyte. The Trasatti plot revealed that the observed high specific capacitance mainly arises from the inner surface charge contribution. The electrode shows the better specific capacity of 329 F g−1 at a current density of 0.6 mA cm−2 in galvanostatic charge-discharge measurements. The electrochemical impedance spectral analysis (EIS) further corroborates that the charge-transfer resistance (Rct) is low in 1 M KOH (2.25 Ω) electrolyte than in 1 M LiOH (9.2 Ω) and 1 M NaOH (50.7 Ω) electrolytes.
SYNTHESIS AND ELECTROCHEMICAL PERFORMANCES OF Γ-KCOPO4 NANOCRYSTALS AS PROMISING ELECTRODE FOR AQUEOUS SUPERCAPATTERIES
(Chemistry Europe, 2019) Natarajan, Priyadharsini; Subramani, Surendran; Baskar, Senthilkumar; Leonid, Vasylechko; Ramakrishnan, Kalai Selvan
Herein, discrete γ-KCoPO4 nanocrystals were prepared by a facile, green and fast sol-gel route. The lattice parameters as well as positional and displacement parameters of atoms in the average γ-KCoPO4 structure with a space group of P21/n were calculated using full profile Rietveld refinement. Monodispersed quadrangular γ-KCoPO4 nanocrystals with improved phase purity and crystallinity were found through XRD patterns and HRTEM images. Subsequently, the prepared γ-KCoPO4 nanocrystals were tested as electrode material for supercapatteries in aqueous electrolytes. The γ-KCoPO4 electrode shows superior specific charge capacity of 309 C g−1 at 1 mV s−1 in 1 M KOH, compared to 1 M NaOH (222 C g−1) and 1 M LiOH (77 C g−1). Further, it exhibits improved electrochemical activity by delivering an impressive specific charge capacity of 100 C g−1 at a current of 0.6 mA cm−2 in an aqueous electrolyte medium with acceptable capacity retention. A lab-scale supercapattery was assembled resembling the commercial device. The fabricated device delivered an enhanced specific energy of 28 W h kg−1 and a specific power of 1600 W kg−1 and prolonged cycle life of about 5000 cycles.