Rohit Ranganathan Gaddam

Spinifex nanocellulose derived hard carbon anodes for high-performance sodium-ion batteries

The selection of an appropriate anode material is a critical factor in dictating the effectiveness of sodium-ion batteries as a cost-effect alternative to lithium-ion batteries. Hard carbon materials sourced from biomass offer the potential for a more sustainable anode material, while also addressing some of the thermodynamic issues associated with using traditional graphite anodes for sodium-ion batteries (NIBs). Herein, we report the preparation of carbon electrode materials from low-cost cellulose nanofibers derived from an Australian native arid grass ‘spinifex’ (Triodia pungens). This nanocellulose derived carbon produced by a fast, low temperature carbonization protocol showed superior performance as an anode for NIBs with a specific capacity (386 mA h g−1 at 20 mA g−1) on par with that of the graphite based anode for lithium-ion batteries, and is one of the highest capacity carbon anodes reported for NIBs. The excellent electrochemical performance is attributed to the large interlayer spacing of the carbon (∼0.39 nm). Superior cycling stability and high rate tolerance (326 mA h g−1 at 50 mA g−1 and 300 mA h g−1 at 100 mA g−1) suggest that hard carbons derived from sustainable precursors are promising for next generation rechargeable batteries.

Capacitance-enhanced sodium-ion storage in nitrogen-rich hard carbon

We demonstrate an approach to prepare nitrogen-rich hard carbon (N-HCS) from biomass as a robust anode material for sodium-ion batteries. A reversible capacity of ∼520 mA h g−1 at a current density of 20 mA g−1 along with an excellent rate performance was obtained. When cycled at a high current density of 1 A g−1, the N-HCS was stable for over 1000 cycles delivering a capacity of ∼204 mA h g−1. Density functional theory (DFT) computations verified that nitrogen doping enhances the interaction of sodium ions with the carbon, leading to a significantly improved storage capacity. This work provides new physical insights into the relationship between sodium-ion storage and nitrogen-containing hard carbon materials.

Porphyrin–graphene oxide frameworks for long life sodium ion batteries

Herein, we demonstrate that a porphyrin interspersed graphene-oxide framework with a d-spacing of ∼7.67 A can significantly enhance the cycling stability of graphene-based anodes in sodium-ion batteries. These robust electrodes can deliver a reversible capacity of ∼200 mA h g−1 at a current density of 100 mA g−1 in the 20th cycle with negligible capacity fading over 700 cycles. In addition to the superior rate tolerance, the specific capacity was stable even after a resting time of one month. The excellent performance may be nested in the larger interlayer spacing, and rich nitrogen content along with the defect sites available for sodium interaction. Experimental studies and density functional theory calculations presented in this work give insights into the structure–property relationship of porphyrin–graphene oxide frameworks and their electrochemical performance.

A reduced graphene oxide-NiO composite electrode with a high and stable capacitance

We report a vacuum-thermal strategy for the preparation of a composite electrode material consisting of reduced graphene oxide and nickel oxide nanoparticles, which displays interesting electrocapacitive properties. Graphene oxide thermally expands in a vacuum and simultaneously nickel(II) acetylacetonate decomposes to form NiO nanoparticles between graphene layers. This method not only allows the uniform dispersion of NiO nanoparticles between graphene layers but also enables simultaneous reduction of graphene oxide. The structural and electrochemical advantages of both reduced graphene oxide and nanoscale NiO particles are maintained. The reduced graphene oxide–NiO composite exhibits a specific capacitance of 880 F g−1 at a current density of 1 A g−1 in 6 M KOH and a 93.1% retention of initial capacitance after 5000 cycles at 5 A g−1.