Electrochemical Performance of Lithium-Ion Hybrid Supercapacitors based on Activated Carbon and Nanoplatelet Li 4 Ti 5 O
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Electrochemical Performance of Lithium-Ion Hybrid Supercapacitors based on Activated Carbon and Nanoplatelet Li4Ti5O12 Insertion Electrode Synthesized by Nanoscission Technique Sandeep Singh1, 2, Alok C Rastogi1, 2, Fredrick Omenya3, M Stanley Whittingham3, Archit Lal4, Shailesh Upreti4 1
Electrical and Computer Engineering, Binghamton University, Binghamton, NY 13902, U.S.A Center for Autonomous Solar Power, Binghamton University, Binghamton, NY 13902, U.S.A 3 Chemistry Department, Binghamton University, Binghamton, NY 13902, U.S.A 4 Primet Precision Materials, Inc., 950 Danby Road, Suite 90, Ithaca, NY 14850, U.S.A 2
ABSTRACT Electrochemical performance of hybrid supercapacitor (HSC) utilizing surface sculpted Li4Ti5O12 (LTO) insertion electrode having nanoplatelet-like morphology and activated carbon (AC) electrode is investigated for energy storage application. Cyclic voltammetry (CV) at variable scan rates 0.5 to 60 mV.s-1 in the 0-3.2 V range show pseusocapacitive behavior and fast rate of current change indicating rapid Faradaic kinetics. Nyquist impedance study show charge transfer resistance due to kinetic effects of electron transfer and Li+ de-intercalation process at the LTO anode. Low capacity (0.2 C-1C) charge-discharge (CD) curves show high Coulomb efficiency with marginal reduction at high 5-10 C rates due to irreversibility of adsorbed PF6 anions at the electrolyte-AC interface. Galvanostatic CD cycling tests over 50 cycles at different C-rates show decline in storage capacity due to electrode polarization effects. Reduction, broadening and shift of the Raman line at 678 cm-1 from Ti-O bonds in TiO6 octahedra after cycling indicates Li insertion reactions in functioning of hybrid supercapacitor. The hybrid supercapacitor cells have shown energy density, 29 Wh.kg-1 and power density, 350 W.kg-1.
INTRODUCTION Energy storage in hybrid supercapacitors (HSC) utilizing an Li insertion anode with battery like functionality and another high surface area cathode with electric double layer (EDLC) charge accumulation function in an organic solvent as an electrolyte is being intensively investigated [1-4]. With the ability for dense energy storage due to Faradaic Li-ion insertion/ extraction processes and high power density arising from reversible fast charge transfer across the EDLC at the interface, such supercapacitors have considerable promise for application in electric and hybrid automotive vehicles. In such an asymmetric electrode based pseudocapacitive energy storage system, a key factor in achieving high energy density and cyclic stability is the Li-insertion anode with stable Li-intercalation property and fast charge-discharge ability. Due to its high energy density and cycling ability, several studies have focused on prelithiated graphite [2], crystalline graphitic carbon [3] anodes, however, at high discharge rates due to the limitation of Li- ion kinetics, their capacitance property show degradation. The Li compounds Li2FeSiO4 [4], Li4Ti5O12 (LTO) [1, 5] have been evaluated as anodes in HSC. LTO
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