Large scale energy storage system with low cost, high power, and long cycle life is crucial for addressing the energy problem when connected with renewable energy production. To realize grid-scale applications of the energy storage devices, there remain several key issues including the development of low-cost, high-performance materials that are environmentally friendly and compatible with low-temperature and large-scale processing. In this report, we demonstrate that solution-exfoliated graphene nanosheets (∼5 nm thickness) can be conformably coated from solution on three-dimensional, porous textiles support structures for high loading of active electrode materials and to facilitate the access of electrolytes to those materials. With further controlled electrodeposition of pseudocapacitive MnO(2) nanomaterials, the hybrid graphene/MnO(2)-based textile yields high-capacitance performance with specific capacitance up to 315 F/g achieved. Moreover, we have successfully fabricated asymmetric electrochemical capacitors with graphene/MnO(2)-textile as the positive electrode and single-walled carbon nanotubes (SWNTs)-textile as the negative electrode in an aqueous Na(2)SO(4) electrolyte solution. These devices exhibit promising characteristics with a maximum power density of 110 kW/kg, an energy density of 12.5 Wh/kg, and excellent cycling performance of ∼95% capacitance retention over 5000 cycles. Such low-cost, high-performance energy textiles based on solution-processed graphene/MnO(2) hierarchical nanostructures offer great promise in large-scale energy storage device applications.

Transparent electrodes, indespensible in displays and solar cells, are currently dominated by indium tin oxide (ITO) films although the high price of indium, brittleness of films, and high vacuum deposition are limiting their applications. Recently, solution-processed networks of nanostructures such as carbon nanotubes (CNTs), graphene, and silver nanowires have attracted great attention as replacements. A low junction resistance between nanostructures is important for decreasing the sheet resistance. However, the junction resistances between CNTs and boundry resistances between graphene nanostructures are too high. The aspect ratios of silver nanowires are limited to ∼100, and silver is relatively expensive. Here, we show high-performance transparent electrodes with copper nanofiber networks by a low-cost and scalable electrospinning process. Copper nanofibers have ultrahigh aspect ratios of up to 100000 and fused crossing points with ultralow junction resistances, which result in high transmitance at low sheet resistance, e.g., 90% at 50 Ω/sq. The copper nanofiber networks also show great flexibility and stretchabilty. Organic solar cells using copper nanowire networks as transparent electrodes have a power efficiency of 3.0%, comparable to devices made with ITO electrodes.

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We report that established simple lithium (Li) ion battery cycles can be used to produce nanopores inside various useful one-dimensional (1D) nanostructures such as zinc oxide, silicon, and silver nanowires. Moreover, porosities of these 1D nanomaterials can be controlled in a stepwise manner by the number of Li-battery cycles. Subsequent pore characterization at the end of each cycle allows us to obtain detailed snapshots of the distinct pore evolution properties in each material due to their different atomic diffusion rates and types of chemical bonds. Also, this stepwise characterization led us to the first observation of pore size increases during cycling, which can be interpreted as a similar phenomenon to Ostwald ripening in analogous nanoparticle cases. Finally, we take advantage of the unique combination of nanoporosity and 1D materials and demonstrate nanoporous silicon nanowires (poSiNWs) as excellent supercapacitor (SC) electrodes in high power operations compared to existing devices with activated carbon.

Li-ion batteries are widely used in current applications such as in cell phones and laptops, and the industry is undergoing rapid expansion. Li-ion batteries are believed to be a major power source for future electrical vehicle applications. [ 1 , 2 ] In a typical Li-ion battery, the electrode materials are electrically contacting the current collector through percolative pathways from conductive additives such as conductive carbons. To increase the total energy stored in a battery, the cells are packed in rolls and stacks and then into modules before fi nal packing in large quantity. [ 2 ] There are dead cell components such as separators, current collectors and packing in Li-ion batteries, which will increase the cost and decrease the total energy density. The total mass of both positive and negative electrode accounts for less than 50% of the total weight. [ 3 ] Traditionally, electrode materials are loaded on the surface of the metal current collector through roll coating methods. The typical thickness for the battery electrode material is ∼ 50 μ m with a mass of ∼ 20 mg/cm 2 . [ 4 ] A higher areal mass loading of battery electrode materials is preferred which will reduce the number of manufacturing steps for achieving the same total energy and also lower the separator costs. However, the traditional architecture of battery electrode materials on fl at metal current collectors does not allow for higher mass loadings due to the following major diffi culties: (1) Thick electrodes tend to delaminate from the fl at current collectors during the high-speed roll-to-roll coating process.(2) The diffi culty of electrolyte penetration through a thick electrode which dramatically increases the cell impedance, and, as a consequence, a loss of energy effi ciency.The concept of three dimensional (3D) battery electrodes has been used previously to enhance the energy per footprint area. [ 5 ] Here we adapt a 3D porous textile conductor as a replacement for metal current collectors. Previously supercapacitors have been demonstrated based on conductive paper and textile. [6][7][8][9][10] Compared with supercapacitor, Li-ion batteries have much higher energy density per weight. Our study here focuses on the development for Li-ion battery application based on the conductive textiles. The electrode materials are loaded into the 3D pores of conductive textiles through the simple solution based process. We found the stable potential range of such conductive textiles in organic electrolyte, and effectively demonstrated a working Li-ion battery with a mass loading of ∼ 168 mg/cm 2 and a thickness of ∼ 600 μ m, which are 8-12 times higher of those on metal collector. Such a thick electrode-current collector architecture shows outstanding performance in capacity retention during cycling and little self-discharge. A control study of electrode materials coated on a fl at metal current collector with the same mass loading shows that the fi lm delaminates from the substrate, and there exists a much larger voltage difference between charg...