In this paper, a simple, cost effective, and scalable process for production of fewlayer graphene is reported by combining ball milling with exfoliants. The graphene was derived from low-cost graphite, which was subjected to high-energy ball milling in an aqueous medium containing a strong exfoliant (1-pyrenecarboxylic acid) and a common solvent methanol. Such a combinatorial approach has not been used before. At a fixed concentration of 1-pyrenecarboxylic acid, the extent of exfoliation was found to be strongly dependent upon the energy input from the ball milling process (expressed as number of hours of milling) and the solvent used. The graphene produced had the distinctive Raman signature, x-ray diffraction crystallinity, scanning electron microscopic image features, transmission electron microscopic images, and high conductivity values (6.7 Â 10 3 S m À1 ) in 4-probe electrical measurements all of which compared reasonably with typical values achieved for few-layer graphene. Application of the few-layer graphene was investigated as an electrode for supercapacitors. The graphene-coated electrode showed good specific capacitance and area capacitance ($176 F g À1 and 1.6 F cm À2 ), superior to conventionally processed graphene. Also demonstrated is good stability in multiple cyclic voltammetric cycles as also a low fade in capacitance after 100 cycles. Based on the obtained characteristics, which show high degree of fidelity when compared to commercial graphene, the few-layer graphene was considered to be a good cost-effective and scalable alternative for applications in energy and other fields. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4809794] 033123-2 Aparna et al. J. Renewable Sustainable Energy 5, 033123 (2013) 033123-5 Aparna et al. J. Renewable Sustainable Energy 5, 033123 (2013) 033123-8 Aparna et al.

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In this study spinel‐lithium manganese oxide (LiMn2O4) powders were prepared by using a simple sol–gel method with polyvinyl alcohol (PVA), and further combined with a conductive additive, graphene, to produce a composite electrode material for improved performance. The effects of the variation in the ratios of binder (PVA) to LiMn2O4 precursor on the particle size and electrochemical behavior of the composite were studied. Particle sizes of <200 nm were obtained. An energy density of 17.36 Wh kg−1 was obtained at an operating voltage of 3.2 V for the pure LiMn2O4 sample tested against a graphene electrode. For simultaneously improving power density (current Li batteries have a low power density as a disadvantage) along with energy density, the LiMn2O4–graphene composite was chosen as an electrode material. LiMn2O4–graphene composite electrodes were prepared by electrophoretic co‐deposition. The ratio of LiMn2O4–graphene composite was optimized to 1:1 during the electrode study based on its electrochemical performance. An average energy density of 30 Wh kg−1, a specific capacity of 49 mAh g−1, and an enhanced power density of 800 W kg−1 at a discharge current of 0.5 A g−1 were obtained. Discharge behavior improved evidently for tests performed on composite electrodes with increased LiMn2O4 (1:1.3 graphene/LiMn2O4). An improved average energy density of 59.6 Wh kg−1 was obtained along with a power density of 697 W kg−1. The electrodes showed good performance during study of a button cell device. Such electrodes are well suited for hybrid energy storage devices having good energy and power density and bridging the gap between batteries and supercapacitors.

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