High performance organic sodium-ion hybrid capacitors based on nano-structured disodium rhodizonate rivaling inorganic hybrid capacitors

Abstract

Sodium hybrid capacitors (NHCs) have tremendous potential to meet the simultaneous high energy–high power requirement of next-generation storage applications. But NHCs still face some obstacles due to poor sodium ion kinetics, low power, and poor cyclability while working with several inorganic sodium ion hosts. Additionally, developing high-performance NHCs that are sustainable and versatile is more crucial from the perspective of energy storage devices. Here, we report a conceptually new and high performance organic sodium hybrid capacitor (ONHC) system, developed by substituting a conventional toxic-metal-containing inorganic battery electrode of an NHC with a nano-structured, metal free, and renewable organic molecule – disodium rhodizonate – to host sodium ions. The sustainability of the ONHC is greatly enhanced by the simultaneous utilization of high surface area cardamom shell (as biomass)-derived porous carbon as a high-power capacitor electrode. The new system exhibits an outstanding performance, delivering a high energy density of ∼87 W h kg⁻¹ along with a high specific power of 10 kW kg⁻¹ (based on the mass in both electrodes), outperforming inorganic sodium hosts. High durability over 10 000 cycles (∼85% retention) with an ultra-low energy loss of ∼0.15% per 100 cycles is also demonstrated, indicating its emergence as a rival to conventional metal containing lithium and sodium hybrid capacitors. The current study provides new opportunities for developing greener and sustainable devices beyond conventional systems for next-generation storage applications.