Sujith Kalluri

Electrical and optical properties of electrospun TiO2-graphene composite nanofibers and its application as DSSC photo-anodes

The present study reports the electrospinning of TiO2-graphene composite nanofibers to develop conductive nano-fiber mats using polyvinylpyrrolidone as a carrier solution. This carrier solution was sublimated at 450 °C to attain a complete conducting continuous nanofibrous network. It was observed during the annealing that as the graphene content was increased to 1 wt% the continuous fiber morphology was lost. Annealing did not have any impact on the fiber diameter (∼150 nm) or morphology as the graphene content was maintained between 0.0–0.7 wt%. The surface porosity of these samples was found be in the range of 45–48%. The presence of graphene in TiO2 nanofibers was confirmed using Raman spectroscopy. Photoluminescence spectroscopy showed excitonic intensity to be lower in graphene-TiO2 samples indicating that the recombination of photo-induced electrons and holes in TiO2 can be effectively inhibited in the composite nanofibers. Fluorescence spectroscopy was used to confirm this phenomenon where blue and quenched emissions were observed for the electrospun TiO2 nanofibers and composite fibers, respectively. Conductivity measurements showed the mean specific conductance values obtained for TiO2-graphene composites to be about two times higher values than that of the electrospun TiO2 fibers. Assembling these TiO2-graphene fiber composites as photoanodes in dye sensitized solar cells, an efficiency of 7.6% was attained.

Electrospun P2-type Na2/3(Fe1/2Mn1/2)O2 Hierarchical Nanofibers as Cathode Material for Sodium-Ion Batteries

Sodium-ion batteries can be the best alternative to lithium-ion batteries, because of their similar electrochemistry, nontoxicity, and elemental abundance and the low cost of sodium. They still stand in need of better cathodes in terms of their structural and electrochemical aspects. Accordingly, the present study reports the first example of the preparation of Na2/3(Fe1/2Mn1/2)O2 hierarchical nanofibers by electrospinning. The nanofibers with aggregated nanocrystallites along the fiber direction have been characterized structurally and electrochemically, resulting in enhanced cyclability when compared to nanoparticles, with initial discharge capacity of ∼195 mAh g(-1). This is attributed to the good interconnection among the fibers, with well-guided charge transfers and better electrolyte contacts.

Electrospun P2-type Na 2/3 (Fe 1/2 Mn 1/2 )O 2 hierarchical nano fibers as cathode material for sodium-ion batteries

Sodium-ion batteries can be the best alternative to lithium-ion batteries, because of their similar electrochemistry, nontoxicity, and elemental abundance and the low cost of sodium. They still stand in need of better cathodes in terms of their structural and electrochemical aspects. Accordingly, the present study reports the first example of the preparation of Na2/3(Fe1/2Mn1/2)O2 hierarchical nanofibers by electrospinning. The nanofibers with aggregated nanocrystallites along the fiber direction have been characterized structurally and electrochemically, resulting in enhanced cyclability when compared to nanoparticles, with initial discharge capacity of ∼195 mAh g(-1). This is attributed to the good interconnection among the fibers, with well-guided charge transfers and better electrolyte contacts.

Sodium and Lithium Storage Properties of Spray-Dried Molybdenum Disulfide-Graphene Hierarchical Microspheres

Developing nano/micro-structures which can effectively upgrade the intriguing properties of electrode materials for energy storage devices is always a key research topic. Ultrathin nanosheets were proved to be one of the potential nanostructures due to their high specific surface area, good active contact areas and porous channels. Herein, we report a unique hierarchical micro-spherical morphology of well-stacked and completely miscible molybdenum disulfide (MoS2) nanosheets and graphene sheets, were successfully synthesized via a simple and industrial scale spray-drying technique to take the advantages of both MoS2 and graphene in terms of their high practical capacity values and high electronic conductivity, respectively. Computational studies were performed to understand the interfacial behaviour of MoS2 and graphene, which proves high stability of the composite with high interfacial binding energy (−2.02 eV) among them. Further, the lithium and sodium storage properties have been tested and reveal excellent cyclic stability over 250 and 500 cycles, respectively, with the highest initial capacity values of 1300 mAh g−1 and 640 mAh g−1 at 0.1 A g−1.

One-dimensional nanostructured design of Li1+x(Mn1/3Ni1/3Fe1/3)O2 as a dual cathode for lithium-ion and sodium-ion batteries

Potency of the cathode material is an important feature for upgrading lithium-ion/sodium-ion battery technology for next-generation applications such as in electrical grids and advanced electric vehicles. Various limitations related to electrochemical and socio-economic issues of these batteries are current research challenges. Amongst the various possible solutions to address such issues, developing nanostructured cathode materials, such as one-dimensional nanostructures, by versatile and easily scaled-up processes could be one of the options. Consequently, in the present study, Li1+x(Mn1/3Ni1/3Fe1/3)O2 one-dimensional nanofibers have been fabricated via a simple and low-cost electrospinning technique and used as a cathode material in lithium-ion batteries, which showed an improved initial reversible capacity (∼109 mA h g−1) and cyclic stability at the 0.1 C rate when compared to the performance of Li1+x(Mn1/3Ni1/3Fe1/3)O2 nanoparticles. On the other hand, the feasibility of this low-cost and eco-friendly material was also tested in sodium-ion batteries, and the same trend is observed. The enhanced electrochemical and structural features in both systems could be ascribed to the exceptional features of one-dimensional nanofibers such as efficient electron transport, facile strain relaxation, and short Li+/Na+ diffusion pathways.

Feasibility of Cathode Surface Coating Technology for High‐Energy Lithium‐ion and Beyond‐Lithium‐ion Batteries

Cathode material degradation during cycling is one of the key obstacles to upgrading lithium-ion and beyond-lithium-ion batteries for high-energy and varied-temperature applications. Herein, we highlight recent progress in material surface-coating as the foremost solution to resist the surface phase-transitions and cracking in cathode particles in mono-valent (Li, Na, K) and multi-valent (Mg, Ca, Al) ion batteries under high-voltage and varied-temperature conditions. Importantly, we shed light on the future of materials surface-coating technology with possible research directions. In this regard, we provide our viewpoint on a novel hybrid surface-coating strategy, which has been successfully evaluated in LiCoO2 -based-Li-ion cells under adverse conditions with industrial specifications for customer-demanding applications. The proposed coating strategy includes a first surface-coating of the as-prepared cathode powders (by sol-gel) and then an ultra-thin ceramic-oxide coating on their electrodes (by atomic-layer deposition). What makes it appealing for industry applications is that such a coating strategy can effectively maintain the integrity of materials under electro-mechanical stress, at the cathode particle and electrode- levels. Furthermore, it leads to improved energy-density and voltage retention at 4.55 V and 45 °C with highly loaded electrodes (≈24 mg.cm-2 ). Finally, the development of this coating technology for beyond-lithium-ion batteries could be a major research challenge, but one that is viable.