Mainul Akhtar1 Subhasish Majumder1

1, IIT Kharagpur, Kharagpur, , India

In present scenario, most widely used electrochemical energy storage systems for consumer electronics are Li-ion batteries and supercapacitors. Conventional cathodes used in lithium ion rechargeable cells cannot meet the requirements of batteries required in electrical vehicles. Bi-material cathodes, comprise of battery and super-capacitors composites, yield high energy as well as high power density rechargeable cells. In this work, we demonstrated that microwave assisted hydrothermally grown carbon coated Na3V2(PO4)3@C (NVP@C) –activated carbon (AC) hybrid electrodes are excellent cathode material for lithium ion rechargeable cells. The as synthesized NVP@C (battery component) and commercially available AC (supercapacitor component) were mixed (40/60 weight ratio) to fabricate bi-material cathode. The electrochemical characteristics of NVP@C, AC and bi-material cathode (NVP@C/AC) were evaluated using 1(M) LiPF6 in EC:DEC (3:7) in half cell configuration using lithium metal as counter and reference electrode. For selected cells full cell characteristics were also studied using Li4Ti5O12 counter electrode. The cells were characterized by cyclic voltammograms, electrochemical impedance spectroscopy, rate capabilities and cycleability. At low specific currents (50 mAg-1), the NVP@C, AC and NVP@C/AC deliver specific capacities of 105, 36 and 66 mAhg-1 with 83%, 93% and 99% capacity retentions respectively after 100 cycles. At high specific currents (700 mAg-1), the NVP@C/AC outperforms both and delivers specific capacity as high as 58 mAhg-1 as compared to 35 and 27 mAhg-1 for NVP@C and AC respectively. The synergistic effect of the bi-material cathode was confirmed by comparing cyclic voltammograms, electrochemical impedance spectra and galvanostatic charge–discharge profiles of these electrodes.