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Fast charging rate and large energy storage are becoming key elements for the development of next-generation batteries, targeting high-performance electric vehicles. Developing electrodes with high volumetric and gravimetric capacity that could be operated at a high rate is the most challenging part of this process. Using silicon as the anode material, which exhibits the highest theoretical capacity as a lithium-ion battery anode, we report a binder-free electrode that interconnects carbon-sheathed porous silicon nanowires into a coral-like network and shows fast charging performance coupled to high energy and power densities when integrated into a full cell with a high areal capacity loading. The combination of interconnected nanowires, porous structure, and a highly conformal carbon coating in a single system strongly promotes the reaction kinetics of the electrode. This leads to fast-charging capability while maintaining the integrity of the electrode without structural collapse and, thus, stable cycling performance without using binder and conductive additives. Specifically, this anode shows high specific capacities (over 1200 mAh g -1 ) at an ultrahigh charging rate of 7 C over 500 charge-discharge cycles. When coupled with a commercial LiCoO 2 or LiFePO 4 cathode in a full cell, it delivers a volumetric energy density of 1621 Wh L -1 with a LiCoO 2 cathode and a power density of 7762 W L -1 with a LiFePO 4 cathode.

Metal oxide nanoparticles decorating graphene have attracted abundant interest in the scientific community owing to their significant application in various areas such as batteries, gas sensors, and photocatalysis. In addition, metal and metal oxide nanoparticles are of great interest for the etching of graphene, for example, to form nanoribbons, through gasification reactions. Hence it is important to have a good understanding of how nanoparticles interact with graphene. In this work we examine, in situ, the behavior of CuO and ZnO nanoparticles on graphene at room temperature while irradiated by electrons in a transmission electron microscope. ZnO is shown to etch graphene through gasification. In the gasification reaction C from graphene is released as CO or CO2. We show that the reaction can occur at room temperature. Moreover, CuO and ZnO particles trapped within a graphene fold are shown to effuse out of a fold through small ruptures. The mass transport in the effusion process between the CuO and ZnO particles is fundamentally different. Mass transport for CuO occurs in an amorphous phase, while for ZnO mass transport occurs through the short-lived gliding of vacancies and dislocations. The work highlights the potential and wealth of electron beam driven chemical reactions of nanomaterials, even at room temperature.

We present electronically controlled field emission characteristics of arrays of individually ballasted carbon nanotubes synthesized by plasma-enhanced chemical vapor deposition on silicon-on-insulator substrates. By adjusting the source-drain potential we have demonstrated the ability to controllable limit the emission current density by more than 1 order of magnitude. Dynamic control over both the turn-on electric field and field enhancement factor have been noted. A hot electron model is presented. The ballasted nanotubes are populated with hot electrons due to the highly crystalline Si channel and the high local electric field at the nanotube base. This positively shifts the Fermi level and results in a broad energy distribution about this mean, compared to the narrow spread, lower energy thermalized electron population in standard metallic emitters. The proposed vertically aligned carbon nanotube field-emitting electron source offers a viable platform for X-ray emitters and displays applications that require accurate and highly stable control over the emission characteristics.