Coconut Sprout-Derived Graphitized Carbon Based Sodium Ion Capacitors

Abstract

Electrochemical Energy storage systems such as rechargeable batteries and supercapacitors play vital role in many applications like portable electronics, electric vehicles, smart electric grids etc. There is always a trade off between the performances of the two devices, with batteries offering high energy density, and supercapacitors exhibiting high power density. Hybrid ion capacitor (HIC), a new concept of energy storage device, wherein the best properties of a battery and a supercapacitor are combined, is attracting lot of interest in recent times.1 Typically, a battery-type electrode is chosen as an anode, while a double layer capacitive electrode forms the cathode in a non-aqueous electrolyte, thus offering intermediate energy and power density compared to batteries and supercapacitors.2 , 3 Recently, sodium based hybrid ion capacitors have been explored due to the large abundance and low cost of sodium.4 ,5 Herein, we report the fabrication of an efficient hybrid sodium ion capacitor, in which the cathode, anode and separator are derived from a single precursor, coconut sprout (CS). Graphene like carbon derived from CS, employed as intercalating anode, exhibits a specific capacity of 181 mAh g- 1, while the high surface area (BET surface area of 2000 m2g-1) activated carbon (obtained by KOH activation of CS) cathode delivers a capacity of 90 mAh g- 1 vs. Na/Na+. Full cell hybrid ion capacitor fabricated combining the two electrodes with optimized mass loading, using CS-derived separator, delivers an energy density of 88.12 Wh kg-1 at a power density 273.26 W kg-1, when cycled in a potential window of 1.5 -4.0 V. The fabricated device retains 65% of its initial capacity after 5000 cycles, when cycled at a high current density of 1A g-1. Most interestingly, the spongy sprout separator showed excellent chemical and mechanical stability even after 10000 cycles of charge and discharge. Several factors including the use of low cost single precursor, facile synthesis route, minimal environmental impact, makes our approach promising towards designing eco-friendly and green electrochemical storage systems. References (1) Amatucci, G. G.; Badway, F.; Du Pasquier, A.; Zheng, T. An Asymmetric Hybrid Nonaqueous Energy Storage Cell. J. Electrochem. Soc. 2001, 148 (8), A930. (2) Ding, J.; Wang, H.; Li, Z.; Cui, K.; Karpuzov, D.; Tan, X.; Kohandehghan, A.; Mitlin, D. Peanut Shell Hybrid Sodium Ion Capacitor with Extreme Energy-Power Rivals Lithium Ion Capacitors. Energy Environ. Sci. 2015, 8 (3), 941–955. (3) Sivakkumar, S. R.; Pandolfo, A. G. Evaluation of Lithium-Ion Capacitors Assembled with Pre-Lithiated Graphite Anode and Activated Carbon Cathode. Electrochim. Acta 2012, 65, 280–287. (4) Ding, J.; Hu, W.; Paek, E.; Mitlin, D. Review of Hybrid Ion Capacitors : From Aqueous to Lithium to Sodium. Chem. Rev. 2018, 118, 6457–6498. (5) B. Babu and M. M. Shaijumon, J. Power Sources 353, 85-94 (2017)