Spinel-structured LiMn 2 O 4 (LMO) is a desirable cathode material for Li-ion batteries due to its low cost, abundance, and high power capability. However, LMO suffers from limited cycle life that is triggered by manganese dissolution into the electrolyte during electrochemical cycling. Here, it is shown that single-layer graphene coatings suppress manganese dissolution, thus enhancing the performance and lifetime of LMO cathodes. Relative to lithium cells with uncoated LMO cathodes, cells with graphene-coated LMO cathodes provide improved capacity retention with enhanced cycling stability. X-ray photoelectron spectroscopy reveals that graphene coatings inhibit manganese depletion from the LMO surface. Additionally, transmission electron microscopy demonstrates that a stable solid electrolyte interphase is formed on graphene, which screens the LMO from direct contact with the electrolyte. Density functional theory calculations provide two mechanisms for the role of graphene in the suppression of manganese dissolution. First, common defects in single-layer graphene are found to allow the transport of lithium while concurrently acting as barriers for manganese diffusion. Second, graphene can chemically interact with Mn 3+ at the LMO electrode surface, promoting an oxidation state change to Mn 4+ , which suppresses dissolution. 1500646(2 of 10) wileyonlinelibrary.com power applications. Furthermore, LMO offers improved thermal stability relative to LiCoO 2 , especially in a highly delithiated state, resulting in safer batteries. [ 6 ] However, a major disadvantage of LMO spinel cathodes is that they lose capacity following long term cycling due to Mn 2+ dissolution from the surface of the cathode into the electrolyte during charge/discharge as a result of the disproportionation reaction: 2Mn 3+ → Mn 4+ + Mn 2+ . [ 7,8 ] Approaches that have shown promise in combating manganese dissolution include modifi cation of the composition of the parent LMO electrode by cation substitution (e.g., LiM x Mn 2x O 4 , M = Li, Co, Ni, Zn) [9][10][11][12][13][14] to reduce the amount of Mn 3+ in the structure, thereby increasing the average oxidation state on the manganese ions in the electrode above 3.5+. In addition, a variety of protective surface oxide coatings have been employed such as Al 2 O 3 , [ 15 ] ZrO 2 , [ 16 ] Y 2 O 3 , [ 17 ] and TiO 2 . [ 7 ] However, the realization of a thin and uniform surface fi lm that does not compromise surface conductivity remains an outstanding challenge.Here, we explore single-layer graphene coatings as an alternative strategy for suppressing manganese dissolution form spinel LMO cathodes. Graphene is a promising candidate for this application since it is an effective diffusion barrier for atomic-scale species [ 18,19 ] and can withstand numerous lithiation charge/discharge cycles. [ 20 ] In addition, graphene is an excellent conductor, which facilitates electron transfer and cycling rate. [ 21 ] Graphene is also known to yield a well-defi ned and stable solid electrolyte interphase (SEI) l...

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Very large scale patterned single-walled carbon nanotube (SWNT) networks were fabricated using a newly developed template guided fluidic assembly process. A mechanism for SWNT assembly and their control is described here. To maximize the directed assembly efficiency of SWNTs toward a wafer level SWNT deposition, Si or SiO(2) substrate was pretreated with precisely controlled SF(6), O(2), and Ar plasma. Chemical and physical properties of the surface were characterized using several surface characterization techniques to investigate and control the mechanism of SWNT assembly. We found that hydrophilic chemical groups such as hydroxides were created on the silicon or silicon oxide surface through the controlled plasma treatment and fluidic SWNT dip-coating process. Also we found that nanoscale rough surface structures formed during the plasma treatment significantly increased the number of dangling bonds and hydroxide functional groups on the surface. These combined chemical and physical enhancements that attract SWNTs in the aqueous solution enable us to build highly organized and very large scale SWNT network architectures effectively in various dimensions and geometries.

Solution-processed semiconductor and dielectric materials are attractive for future lightweight, low-voltage, flexible electronics, but their response to ionizing radiation environments is not well understood. Here, we investigate the radiation response of graphene field-effect transistors employing multilayer, solution-processed zirconia self-assembled nanodielectrics (Zr-SANDs) with ZrOx as a control. Total ionizing dose (TID) testing is carried out in situ using a vacuum ultraviolet source to a total radiant exposure (RE) of 23.1 μJ/cm(2). The data reveal competing charge density accumulation within and between the individual dielectric layers. Additional measurements of a modified Zr-SAND show that varying individual layer thicknesses within the gate dielectric tuned the TID response. This study thus establishes that the radiation response of graphene electronics can be tailored to achieve a desired radiation sensitivity by incorporating hybrid organic-inorganic gate dielectrics.

Efforts aimed at large-scale integration of nanoelectronic devices that exploit the superior electronic and mechanical properties of single-walled carbon nanotubes (SWCNTs) remain limited by the difficulties associated with manipulation and packaging of individual SWNTs. Alternative approaches based on ultrathin carbon nanotube networks (CNNs) have enjoyed success of late with the realization of several scalable device applications. However, precise control over the network electronic transport is challenging due to (i) an often uncontrollable interplay between network coverage and its detailed topology and (ii) the inherent electrical heterogeneity of the constituent SWNTs. In this article, we use template-assisted fluidic assembly of SWCNT networks to explore the effect of geometric confinement on the network topology. Heterogeneous SWCNT networks dip-coated onto submicrometer wide ultrathin polymer channels become increasingly aligned with decreasing channel width and thickness. Experimental-scale coarse-grained computations of interacting SWCNTs show that the effect is a reflection of a topology that is no longer dependent on the network density, which in turn emerges as a robust knob that can induce semiconductor-to-metallic transitions in the network response. Our study demonstrates the effectiveness of directed assembly on channels with varying degrees of confinement as a simple tool to tailor the conductance of the otherwise heterogeneous network, opening up the possibility of robust large-scale CNN-based devices.