All Coconut Sprout Sodium Ion Hybrid Capacitor

Abstract

Electrochemical Energy storage systems play a vital role in many applications like electronics, automotive, aerospace, smart electric grids etc. There are mainly two types of energy storage systems known as batteries and supercapacitors. The first one offers high energy density, and the later one is well known for its power density. Hybrid ion capacitor (HIC) is a new class of energy storage device, a combination of battery and supercapacitor1. Commonly anode part in HIC is taken from a battery, and the cathode part will be from a capacitor and in principle, the duo offers intermediate energy and power density in comparison with batteries and supercapacitors2 3. Sodium based hybrid capacitors are extensively explored today due to large abundance and low cost of sodium4. Here in we report for the first-time, fabrication of a hybrid sodium ion capacitor, in which the cathode, anode and separator are derived from a single precursor called coconut sprout (CS). Graphene-like carbon derived from CS, employed as an intercalating anode, provides a specific capacity of 181.09 mAhg- 1. High surface area (BET surface area of 2000 m2g-1) ion adsorption cathode part obtained by KOH activation of CS delivers a capacity of 90.15 mAhg- 1. Combination of CS derived anode, cathode and separator give rise to a capacitor works in a potential window of 1.5 -4.0V. The all sprout capacitor could deliver an energy density of 88.12 Whkg-1 at power density 273.26 Wkg-1 and energy density of 25.07 Whkg-1 at power density 7078 Wkg-1. This green, all sprout hybrid capacitor retained 65% of its initial capacity after 5000 cycles, while cycled at a current density of 1Ag-1. The spongy sprout separator showed excellent chemical and mechanical stability even after 10000 cycles of charge and discharge. Though the performance is not outstanding, low cost single precursor, facile synthesis route, minimal environmental impact of the device makes it a promising candidate among eco-friendly electrochemical systems. Reference (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.