Praveen Meduri

Hybrid Tin Oxide Nanowires as Stable and High Capacity Anodes for Li-Ion Batteries

In this report, we present a simple and generic concept involving metal nanoclusters supported on metal oxide nanowires as stable and high capacity anode materials for Li-ion batteries. Specifically, SnO(2) nanowires covered with Sn nanoclusters exhibited an exceptional capacity of >800 mAhg(-1) over hundred cycles with a low capacity fading of less than 1% per cycle. Post lithiation analyses after 100 cycles show little morphological degradation of the hybrid nanowires. The observed, enhanced stability with high capacity retention is explained with the following: (a) the spacing between Sn nanoclusters on SnO(2) nanowires allowed the volume expansion during Li alloying and dealloying; (b) high available surface area of Sn nanoclusters for Li alloying and dealloying; and (c) the presence of Sn nanoclusters on SnO(2) allowed reversible reaction between Sn and Li(2)O to produce both Sn and SnO phases.

Hollow core–shell structured porous Si–C nanocomposites for Li-ion battery anodes

Hollow core–shell structured porous Si–C nanocomposites with void space up to tens of nanometres are designed to accommodate the volume expansion during lithiation for high-performance Li-ion battery anodes. An initial capacity of ∼760 mA h g−1 after formation cycles (based on the entire electrode weight) with ∼86% capacity retention over 100 cycles is achieved at a current density of 1 A g−1. Good rate performance is also demonstrated.

MoO 3−x Nanowire Arrays As Stable and High-Capacity Anodes for Lithium Ion Batteries

In this study, vertical nanowire arrays of MoO(3-x) grown on metallic substrates with diameters of ~90 nm show high-capacity retention of ~630 mAhg(-1) for up to 20 cycles at 50 mAg(-1) current density. Particularly, they exhibit a capacity retention of ~500 mAhg(-1) in the voltage window of 0.7-0.1 V, much higher than the theoretical capacity of graphite. In addition, 10 nm Si-coated MoO(3-x) nanowire arrays have shown a capacity retention of ~780 mAhg(-1), indicating that hybrid materials are the next generation materials for lithium ion batteries.

Conductive Rigid Skeleton Supported Silicon as High-Performance Li-Ion Battery Anodes

A cost-effective and scalable method is developed to prepare a core-shell structured Si/B(4)C composite with graphite coating with high efficiency, exceptional rate performance, and long-term stability. In this material, conductive B(4)C with a high Mohs hardness serves not only as micro/nano-millers in the ball-milling process to break down micron-sized Si but also as the conductive rigid skeleton to support the in situ formed sub-10 nm Si particles to alleviate the volume expansion during charge/discharge. The Si/B(4)C composite is coated with a few graphitic layers to further improve the conductivity and stability of the composite. The Si/B(4)C/graphite (SBG) composite anode shows excellent cyclability with a specific capacity of ∼822 mAh·g(-1) (based on the weight of the entire electrode, including binder and conductive carbon) and ∼94% capacity retention over 100 cycles at 0.3 C rate. This new structure has the potential to provide adequate storage capacity and stability for practical applications and a good opportunity for large-scale manufacturing using commercially available materials and technologies.

Ionic liquid-enhanced solid state electrolyte interface (SEI) for lithium–sulfur batteries

Li–S batteries are a complicated system with many challenges existing before their final market penetration. While most of the reported work for Li–S batteries is focused on the cathode design, we demonstrate in this work that the anode consumption accelerated by corrosive polysulfide solution also critically determines the Li–S cell performance. To validate this hypothesis, ionic liquid (IL) N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI) has been employed to modify the properties of the SEI layer formed on the Li metal surface in Li–S batteries. It is found that the IL-enhanced passivation film on the lithium anode surface exhibits very different morphology and chemical composition, effectively protecting lithium metal from continuous attack by soluble polysulfides. Therefore, both the cell impedance and the irreversible consumption of polysulfides on lithium metal are reduced. As a result, the Coulombic efficiency and the cycling stability of Li–S batteries have been greatly improved. After 120 cycles, the Li–S battery cycled in the electrolyte containing 75% IL demonstrates a high capacity retention of 94.3% at 0.1 C rate. These results reveal one of the main failure mechanisms in Li–S batteries and shine the light on new approaches to improve the reversible capacity and cyclability of Li–S batteries. This work provides important clues for the understanding and thus the improvement of Li–S battery systems through a different point of view.

Kinetically limited de-lithiation behavior of nanoscale tin-covered tin oxide nanowires

In this paper, we report that Sn-nanocluster-covered SnO2 nanowire (“hybrid architectures”) electrodes exhibited stage-wise de-lithiation suggesting complete lithium extraction. The lithiation and de-lithiation behavior explains that the high capacity retention of 814 mAh g−1 and durability over hundred cycles is because of low irreversible capacity loss. Mono-layers of un-agglomerated, sub 60 nm size Sn clusters supported on metallic electrodes also exhibited similar stage-wise de-lithiation while the microscale Sn clusters exhibited single-phase lithium extraction. This can be attributed to shorter lithium ion diffusion lengths and high surface area of the nanomaterials. The cyclic voltammetric studies of Sn nanoclusters (sub 60 nm size) confirm the reaction kinetics limited behavior of lithiation and de-lithiation characteristics. The Sn-nanocluster-covered SnO2 nanowires showed a capacity retention of 458 mAh g−1 at 500 mAg−1 current density indicating an excellent rate capability.

Tunable electrochemical properties of fluorinated graphene

The structural and electrochemical properties of fluorinated graphene have been investigated by using a series of graphene fluorides (CFx, x = 0.47, 0.66, 0.89). Fluorinated graphene exhibited high capacity retentions of 75–81% of theoretical capacity at moderate rates as cathode materials for primary lithium batteries. Specifically, CF0.47 maintained a capacity of 356 mA h g−1 at a 5 C rate, superior to that of traditional fluorinated graphite. The discharged graphene fluorides also provide an electrochemical tool to probe the chemical bonding on the parent graphene substrate.

Inorganic nanowires: a perspective about their role in energy conversion and storage applications

There has been tremendous interest and progress with synthesis of inorganic nanowires (NWs). However, much of the progress only resulted in NWs with diameters much greater than their respective quantum confinement scales, i.e. 10?100?nm. Even at this scale, NW-based materials offer enhanced charge transport and smaller diffusion length scales for improved performance with various electrochemical and photoelectrochemical energy conversion and storage applications. In this paper, these improvements are illustrated with specific results on enhanced charge transport with tin oxide NWs in dye sensitized solar cells, higher capacity retention with molybdenum oxide (MoO3) NW arrays and enhanced photoactivity with hematite NW arrays compared with their nanoparticle (NP) or thin film format counterparts. In addition, the NWs or one-dimensional crystalline materials with diameters less than 100?nm provide a useful platform for creating new materials either as substrates for heteroepitaxy or through the phase transformation with reaction. Specific results with single crystal phase transformation of hematite (a-Fe2O3) to pyrite (FeS2) NWs and heteroepitaxy of indium-rich InGaN alloy over GaN NW substrates are presented to illustrate the viability of using NWs for creating new materials. In terms of energy applications, it is essential to have a method for continuous manufacturing of vertical NW arrays over large areas. In this regard, a simple plasma-based technique is discussed that potentially could be scaled up for roll-to-roll processing of NW arrays.

Production of High Value Cellulose from Tobacco

The Kentucky Rural Energy Supply Program was established in 2005 by a federal direct appropriation to benefit the citizens of the Commonwealth by creating a unified statewide consortium to promote renewable energy and energy efficiency in Kentucky. The U.S. Department of Energys (DOE) Office of Biomass Programs initially funded the consortium in 2005 with a

Hybrid CFx–Ag2V4O11 as a high-energy, power density cathode for application in an underwater acoustic microtransmitter

2 million operational grant. The Kentucky Rural Energy Consortium (KREC) was formed at the outset of the program to advance energy efficiency and comprehensive research on biomass and bioenergy of importance to Kentucky agriculture, rural communities, and related industries. In recognition of the successful efforts of the program, KREC received an additional