Composites of Si nanoparticles highly dispersed between graphene sheets, and supported by a 3-D network of graphite formed by reconstituting regions of graphene stacks exhibit high Li ion storage capacities and cycling stability. An electrode was prepared with a storage capacity >2200 mA h g(-1) after 50 cycles and >1500 mA h g(-1) after 200 cycles that decreased by <0.5% per cycle.

The unique combination of high surface area, high electrical conductivity and robust mechanical integrity has attracted great interest in the use of graphene sheets for future electronics applications. Their potential applications for high-power energy storage devices, however, are restricted by the accessible volume, which may be only a fraction of the physical volume, a consequence of the compact geometry of the stack and the ion mobility. Here we demonstrated that remarkably enhanced power delivery can be realized in graphene papers for the use in Li-ion batteries by controlled generation of in-plane porosity via a mechanical cavitation-chemical oxidation approach. These flexible, holey graphene papers, created via facile microscopic engineering, possess abundant ion binding sites, enhanced ion diffusion kinetics, and excellent high-rate lithium-ion storage capabilities, and are suitable for high-performance energy storage devices.

The current insatiable appetite for more effi cient electrical energy storage devices with a fl exible and/or compact confi guration, fed by the proliferation of portable electronics with ever increasing functional complexity, will be even more diffi cult to satisfy when electrifi ed vehicles become the preferred mode of transportation, and energy harvesting from intermittent sources evolves into the practiced norm. [1][2][3][4] Incorporation of the attractive features of supercapacitors with high rate performance and rechargeable batteries with high energy densities into a single unit would enable the design of high-capacity energy storage devices for sustainable power delivery. [5][6][7] Thus far, however, this goal has proved to be diffi cult to attain. Strategies used to boost the power capability of electrode materials for Li-ion batteries generally involve reducing the domain size of the active charge-storage material (e.g., Si) in the electrode to shorten the ion diffusion paths, such as by fabricating vertically aligned 1-D nanostructures or ultrathin coatings on nanofoams and metallic mesh. [ 8 , 9 ] Generally, such an approach suffers from limited overall charge storage capacity due to a low mass fraction of the active component in the electrode. Fabricating porous electrode frameworks using sacrifi cial templates is another approach, [10][11][12] but these porous electrodes introduce different problems, such as confi gurational infl exibility imposed by mechanical fragility and a dramatic drop in volumetric energy density consequential of reduced packing densities. Here we demonstrate that graphene sheets possessing a high density of in-plane, -sized carbon vacancies can be transformed into a fl exible, 3-D conducting graphenic scaffold with excellent crossplane ion diffusivity and tolerance to structural deformation. When employed as a structural platform to incorporate high storage-capacity materials, such as Si, a stable, self-supporting composite electrode with enhanced accessible interior and high rate capacity is obtained, representing an attractive electrode candidate towards high-performance Li-ion batteries. Furthermore, the composite is ductile and offers confi gurational fl exibility, and can be produced by cost-effective processes.Our 3-D graphenic scaffold was constructed with aligned graphene sheets, derived from exfoliated graphene oxide sheets into which in-plane, nm-sized carbon vacancies were introduced by a facile wet chemical method. It confers a combination of advantageous features over reported electrodes systems: i) Facile ion transport throughout the structure, enabled by new diffusion channels created with in-plane carbon vacancies. This overcomes the characteristic high resistance of graphene material for Li ion transport due to their extreme width-to-thickness aspect ratio and inter-sheet aggregation. [13][14][15][16][17] ii) Superior electrical conductivity and high packing density derived from the compact structure of interconnecting graphitic domains. [ 18 , 19 ] iii) S...

The lithium-ion battery is the most promising battery candidate to power battery-electric vehicles. For these vehicles to be competitive with those powered by conventional internal combustion engines, significant improvements in battery performance are needed, especially in the energy density and power delivery capabilities. Recent discoveries and advances in the development of electrode materials to improve battery performance are summarized. Promising substitutes for graphite as the anode material include silicon, tin, germanium, their alloys, and various metal oxides that have much higher theoretical storage capacities and operate at slightly higher and safer potentials. Designs that attempt to accommodate strain owing to volumetric changes upon lithiation and delithiation are presented. All known cathode materials have storage capacities inferior to those of anode materials. In addition to variations on known transition metal oxides and phosphates, other potential materials, such as metal fluorides, are discussed as well as the effects of particle size and electrode architecture. New electrolyte systems and additives as well as their effects on battery performance, especially with regard to safety, are described.

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