Anisotropic Carbon Nanotube Structures with High Aspect Ratio Nanopores for Li-Ion Battery Anodes

Technological advances in membrane technology, catalysis, and electrochemical energy storage require the fabrication of controlled pore structures at ever smaller length scales. It is therefore important to develop processes allowing for the fabrication of materials with controlled submicron porous structures. We propose a combination of colloidal lithography and chemical vapor deposition of carbon nanotubes to create continuous straight pores with diameters down to 100 nm in structures with thicknesses of more than 300 μm. These structures offer unique features, including continuous and parallel pores with aspect ratios in excess of 3000, a low pore tortuosity, good electrical conductivity, and electrochemical stability. We demonstrate that these structures can be used in Li-ion batteries by coating the carbon nanotubes with Si as an active anode material

Hydrothermal Coating of Patterned Carbon Nanotube Forest for Structured Lithium-Ion Battery Electrodes.

Controlling the arrangement and interface of nanoparticles is essential to achieve good transfer of charge, heat, or mechanical load. This is particularly challenging in systems requiring hybrid nanoparticle mixtures such as combinations of organic and inorganic materials. This work presents a process to coat vertically aligned carbon nanotube (CNT) forests with metal oxide nanoparticles using microwave-assisted hydrothermal synthesis. Hydrothermal processes normally damage delicate CNT forests, which is addressed here by a combination of lithographic patterning, transfer printing, and reduction of the synthesis time. This process is applied for the fabrication of structured Li-ion battery (LIB) electrodes where the aligned CNTs provide a straight electron transport path through the electrode and the hydrothermal coating process is used to coat the CNTs with conversion anode materials for LIBs. These nanoparticles are anchored on the surface of the CNTs and batteries fabricated following this process show a fourfold longer cyclability. Finally, this process is used to create thick electrodes (350 µm) with a gravimetric capacity of over 900 mAh g-1

Honeycomb-shaped carbon nanotube supports for BiVO4 based solar water splitting.

Advances in the synthesis and assembly of nanomaterials offer a unique opportunity to purposefully design structures according to the requirements of the targeted applications. This paper shows a process to create robust 3D carbon nanotube (CNT) structures, which provide an electrically conductive support for nanoparticle coating. We describe a process to reliably fabricate robust honeycomb structures with walls made out of aligned CNTs. We present a design of experimental analysis of this fabrication process and discuss methods to coat these honeycombs with BiVO4 for solar fuel applications. The proposed honeycomb structure allows for an efficient transport of electrons through the electrode, as well as an enhanced light-electrode interaction. Finally, we demonstrate that the developed CNT electrodes can survive harsh BiVO4 synthesis conditions and can subsequently be used as photoelectrodes for solar water splitting

Continuous flow chemical vapour deposition of carbon nanotube sea urchins

Hybrid structures consisting of functional materials enhanced by carbon nanotubes (CNTs) have potential for a variety of high impact applications, as shown by the impressive progress in sensing and mechanical applications enabled by CNT-enhanced materials. The hierarchical organisation of CNTs with other materials is key to the design of macroscale devices benefiting from the unique properties of individual CNTs, provided CNT density, morphology and binding with other materials are optimized. In this paper, we provide an analysis of a continuous aerosol process to create a hybrid hierarchical sea urchin structure with CNTs organized around a functional metal oxide core. We propose a new mechanism for the growth of these carbon nanotube sea urchins (CNTSU) and give new insight into their chemical composition. To corroborate the new mechanism, we examine the influence of CNT growth conditions on CNTSU morphology and demonstrate a new in-line characterisation technique to continuously monitor aerosol CNT growth during synthesis, which enables industrial-scale production optimization. Based upon the new formation mechanism we describe the first substrate-based chemical vapour deposition growth of CNTSUs which increases CNT length and improves G to D ratio, which also allows for the formation of CNTSU carpets with unique structures

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Transcatheter aortic valve-in-valve implantation and sutureless aortic valve replacement: two strategies for one goal in redo patients

BACKGROUND: The most appropriate approach for high-risk patients with degenerated bioprostheses remains a matter of debate. The aim of the study was to evaluate the clinical and hemodynamic outcome of redo patients undergoing transcatheter aortic valve-in-valve implantation (VinV-TAVI) and sutureless aortic valve replacement (AVR), with assessment of patient-prosthesis mismatch (PPM) in the perioperative and follow-up period. METHODS: From 2010, 343 patients underwent TAVI and 220 patients underwent sutureless AVR at our institution. Among these, 14 patients had prior bioprosthetic AVR and indication for reintervention because of valve degeneration. Patients from the TAVI group (N.=6) underwent VinV-TAVI, and patients from the sutureless group (N.=8) underwent redo AVR. RESULTS: Mean age was 78.8±3 years in the sutureless group and 80.2±2.3 in the VinV-TAVI group. Logistic EuroSCORE was 36.4±24.1% and 33.8±13.8% in the sutureless and VinV-TAVI group, respectively. There was no in-hospital death. No patient was lost to follow-up (21±13 months, range 6 to 42). Quality of life measured with the EQ-5D questionnaire improved by 65% in the sutureless group and by 67% in the VinV-TAVI group. At follow-up echocardiographic evaluation, no paravalvular leak or intraprosthetic regurgitation was observed in either group. The mean iEOA was 0.96±0.08 vs. 0.71±0.15 cm2/m2 in the sutureless vs. VinV-TAVI group. CONCLUSIONS: In patients undergoing redo aortic valve surgery for degenerated bioprostheses, both VinV-TAVI and sutureless AVR are effective in terms of clinical outcome. As regards echocardiographic evaluation, no leak was observed in either group and no cases of severe PPM were recorded in the sutureless group

Carbon nanotube conductive additives for improved electrical and mechanical properties of flexible battery electrodes

Flexible electronics are being pursued as replacements for rigid consumer electronic products such as smartphones and tablets, as well as for wearable electronics, implantable medical devices, and RFIDs. Such devices require flexible batteries with electrodes that maintain their electro-chemical performance during multiple bending cycles. These electrodes typically consist of an active battery material blend with a conductive additive and a binder. Whilst the choice of active battery material is typically dictated by the desired battery power and energy requirements, there is more freedom in changing the conductive additives to cope with strain induced during the bending of flexible batteries. Here we compare the mechanical and electrical properties of free standing cathodes using lithium cobalt oxide (LiCoO2) as the active material and 10–20 wt% of amorphous carbon powder (CP) or carbon nanotubes (CNTs) as conductive additives. We found that the CNT based electrodes showed less crack formation during bending and have a Young's modulus up to 30 times higher than CP electrodes (10 wt% loading). Further, the electrical resistance of pristine CNT electrodes is 10 times lower than CP electrodes (20 wt% loading). This difference further increases to a 28 times lower resistance for CNT films after 2000 bending cycles. These superior properties of CNT films are reflected in the electrochemical tests, which show that after bending, only the electrodes with 20 wt% of CNTs remain operational. This study therefore highlights the importance of the conductive additives for developing reliable flexible batteries

Carbon nanotube conductive additives for improved electrical and mechanical properties of flexible battery electrodes

Flexible electronics are being pursued as replacements for rigid consumer electronic products such as smartphones and tablets, as well as for wearable electronics, implantable medical devices, and RFIDs. Such devices require flexible batteries with electrodes that maintain their electro-chemical performance during multiple bending cycles. These electrodes typically consist of an active battery material blend with a conductive additive and a binder. Whilst the choice of active battery material is typically dictated by the desired battery power and energy requirements, there is more freedom in changing the conductive additives to cope with strain induced during the bending of flexible batteries. Here we compare the mechanical and electrical properties of free standing cathodes using lithium cobalt oxide (LiCoO2) as the active material and 10 to 20 wt% of amorphous carbon powder (CP) or carbon nanotubes (CNTs) as conductive additives. We found that the CNT based electrodes showed less crack formation during bending and have a Young's modulus up to 30 times higher than CP electrodes (10 wt% loading). Further, the electrical resistance of pristine CNT electrodes is 10 times lower than CP electrodes (20 wt% loading). This difference further increases to a 28 times lower resistance for CNT films after 2000 bending cycles. These superior properties of CNT films are reflected in the electrochemical tests, which show that after bending, only the electrodes with 20 wt% of CNTs remain operational. This study therefore highlights the importance of the conductive additives for developing reliable flexible batteries