Ranjith Thangavel

Engineering the Pores of Biomass‐Derived Carbon: Insights for Achieving Ultrahigh Stability at High Power in High‐Energy Supercapacitors

Electrochemical supercapacitors with high energy density are promising devices due to their simple construction and long-term cycling performance. The development of a supercapacitor based on electrical double-layer charge storage with high energy density that can preserve its cyclability at higher power presents an ongoing challenge. Herein, we provide insights to achieve a high energy density at high power with an ultrahigh stability in an electrical double-layer capacitor (EDLC) system by using carbon from a biomass precursor (cinnamon sticks) in a sodium ion-based organic electrolyte. Herein, we investigated the dependence of EDLC performance on structural, textural, and functional properties of porous carbon engineered by using various activation agents. The results demonstrate that the performance of EDLCs is not only dependent on their textural properties but also on their structural features and surface functionalities, as is evident from the electrochemical studies. The electrochemical results are highly promising and revealed that the porous carbon with poor textural properties has great potential to deliver high capacitance and outstanding stability over 300 000 cycles compared with porous carbon with good textural properties. A very low capacitance degradation of around 0.066 % per 1000 cycles, along with high energy density (≈71 Wh kg-1 ) and high power density, have been achieved. These results offer a new platform for the application of low-surface-area biomass-derived carbons in the design of highly stable high-energy supercapacitors.

Cu-doped P2-Na0.5Ni0.33Mn0.67O2 encapsulated with MgO as a novel high voltage cathode with enhanced Na-storage properties

We report a novel P2-type Na0.5Ni0.26Cu0.07Mn0.67O2 (NCM) mixed oxide obtained by conventional solid-state method as a prospective cathode for sodium-ion battery (SIB) applications. X-ray diffraction analysis shows that NCM exhibits a hexagonal structure with a P63/mmc (No. 194) space group, in which Na-ions are located in a prismatic environment. The introduction of Cu into the lattice enhances its structural stability, showing a capacity retention of 83% after 100 cycles, which is much better than its native compound. MgO encapsulation was performed to further improve the interfacial kinetics and suppress P2–O2 phase transition. MgO coating significantly improves the electrochemical activity at high cut-off voltages, for instance, highest capacity of 131 mA h g−1 was noted with superior rate performance of 83 and 51 mA h g−1 at 5 and 20C, respectively. As expected, dual modification by Cu-ion doping and MgO coating provides a novel strategy for designing high-rate SIB cathodes.

High Volumetric Energy Density Hybrid Supercapacitors Based on Reduced Graphene Oxide Scrolls

The low volumetric energy density of reduced graphene oxide (rGO)-based electrodes limits its application in commercial electrochemical energy storage devices that require high-performance energy storage capacities in small volumes. The volumetric energy density of rGO-based electrode materials is very low due to their low packing density. A supercapacitor with enhanced packing density and high volumetric energy density is fabricated using doped rGO scrolls (GFNSs) as the electrode material. The restacking of rGO sheets is successfully controlled through synthesizing the doped scroll structures while increasing the packing density. The fabricated cell exhibits an ultrahigh volumetric energy density of 49.66 Wh/L with excellent cycling stability (>10 000 cycles). This unique design strategy for the electrode material has significant potential for the future supercapacitors with high volumetric energy densities.

Rapidly Synthesized, Few-Layered Pseudocapacitive SnS2 Anode for High-Power Sodium Ion batteries

The abundance of sodium resources has recently motivated the investigation of sodium ion batteries (SIBs) as an alternative to commercial lithium ion batteries. However, the low power and low capacity of conventional sodium anodes hinder their practical realization. Although most research has concentrated on the development of high-capacity sodium anodes, anodes with a combination of high power and high capacity have not been widely realized. Herein, we present a simple microwave irradiation technique for obtaining few-layered, ultrathin two-dimensional SnS2 over graphene sheets in a few minutes. SnS2 possesses a large number of active surface sites and exhibits high-capacity, rapid sodium ion storage kinetics induced by quick, nondestructive pseudocapacitance. Enhanced sodium ion storage at a high current density (12 A g-1), accompanied by high reversibility and high stability, was demonstrated. Additionally, a rationally designed sodium ion full cell coupled with SnS2//Na3V2(PO4)3 exhibited exceptional performance with high initial Coulombic efficiency (99%), high capacity, high stability, and a retention of ∼53% of the initial capacity even after the current density was increased by a factor of 140. In addition, a high specific energy of ∼140 Wh kg-1 and an ultrahigh specific power of ∼8.3 kW kg-1 (based on the mass of both the anode and cathode) were observed. Because of its outstanding performance and rapid synthesis, few-layered SnS2 could be a promising candidate for practical realization of high-power SIBs.

Highly interconnected hollow graphene nanospheres as an advanced high energy and high power cathode for sodium metal batteries

Developing sodium based energy storage systems that retain high energy density at high power along with stable cycling is of paramount importance to meet the energy demands of next generation applications. This requires the development of electrodes beyond the conventional intercalation-based chemistry to overcome the sluggish diffusion-limited reaction kinetics and limited cycle life. Herein, we report a rationally designed hollow graphene nanosphere (HGS) cathode, which utilizes non-destructive, ultra-fast surface redox reactions at oxygen functional groups and delivers a discharge capacity of ∼155 mA h g−1 (0.1 A g−1) corresponding to a high energy of ∼415 W h kg−1 and retains ∼88 W h kg−1 of energy at a remarkable specific power of ∼84 kW kg−1 (40 A g−1), which are beyond the capabilities of intercalation-based electrodes. Moreover, the achieved cycling performance (86% capacity retention after 50 000 cycles at 10 A g−1) is the most stable cathode performance reported so far. The rationally designed sodium metal battery full cells with a sodium metal deposited aluminium current collector anode and the HGS cathode showed a similar sodium ion storage performance with high capacity, good rate capability, and stability. We certainly believe that the current research could direct the future research development towards transition metal-free, ultra-high power and super stable cathodes for sodium energy storage devices.

An Efficient Method of Designing Stable Layered Cathode Material for Sodium Ion Batteries Using Aluminum Doping

Despite their high specific capacity, sodium layered oxides suffer from severe capacity fading when cycled at higher voltages. This key issue must be addressed in order to develop high-performance cathodes for sodium ion batteries (SIBs). Herein, we present a comprehensive study on the influence of Al doping of Mn sites on the structural and electrochemical properties of a P2-Na0.5Mn0.5-xAlxCo0.5O2 (x = 0, 0.02, or 0.05) cathode for SIBs. Detailed structural, morphological, and electrochemical investigations were carried out using X-ray diffraction, cyclic voltammetry, and galvanostatic charge-discharge measurements, and some new insights are proposed. Rietveld refinement confirmed that Al doping caused TMO6 octahedra (TM = transition metal) shrinkage, resulting in wider interlayer spacing. After optimizing the aluminum concentration, the cathode exhibited remarkable electrochemical performance, with better stability and improved rate performance. Electrochemical impedance spectroscopy (EIS) measurements were performed at various states of charge to probe the surface and bulk effects of Al doping. The material presented here exhibits exceptional stability over 100 cycles within a 1.5-4.3 V window and outperforms several other Mn-Co-based cathodes for SIBs. This study presents a facile method for designing structurally stable cathodes for SIBs.

Nitrogen- and sulfur-enriched porous carbon from waste watermelon seeds for high-energy, high-temperature green ultracapacitors

Electrochemical ultracapacitors exhibiting high energy output and an ultra-long cycle life, utilizing green and sustainable materials, are of paramount importance for next-generation applications. Developing an ultracapacitor that has high output energy under high power conditions in a high-voltage non-aqueous electrolyte and maintaining a long cycle life is an ongoing challenge. Herein, we utilize watermelon seeds, a bio-waste from watermelons, for use in high-voltage, high-energy, and high-power ultracapacitors in a sodium ion-based non-aqueous electrolyte. The as-synthesized hierarchically porous, high surface area carbon is surface-engineered with a large quantity of nitrogen and sulfur heteroatoms to give a high specific capacitance of ∼252 F g−1 at 0.5 A g−1 and 90 F g−1 at 30 A g−1. An ultra-high stability of ∼90% even after 150 000 cycles (10 A g−1) with 100% coulombic efficiency is achieved at room temperature (25 °C), equivalent to an ultra-low energy loss of ∼0.0667% per 1000 cycles. Furthermore, the porous carbon demonstrates remarkable stability even at high temperature (55 °C) for 100 000 cycles (10 A g−1), ensuring the safety of the device and enabling it to outperform graphene-based materials. A maximum energy of ∼79 W h kg−1 and a maximum power of 22.5 kW kg−1 with an energy retention of ∼28.2 W h kg−1 was attained. The results provide new insights that will be of use in the development of high-performance, green ultracapacitors for advanced energy storage systems.

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

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.