Nanoscale & Nanoscale Advances Blog

New Nanoscale Communication

Enhanced cycleability of LiMn2O4 cathodes by atomic layer deposition of nanosized-thin Al2O3 coatings

Dongsheng Guan, Judith A. Jeevarajan and Ying Wang

Nanoscale, DOI: 10.1039/c0nr00939c

A group of scientists in America have developed a method to put an Al₂O₃ ‘nano-coating’ on LiMn₂O₄ cathodes, which results in significantly enhanced performance of the cathode. They claim that this method can be generalised to other electrode materials and a variety of surface coatings in order to significantly improve battery performance.

LiMn₂O₄ has been widely investigated for use in lithium-ion batteries due to its unique advantages such as high specific capacity and output voltage, and the fact that it is low-cost, abundant and environmentally friendly. However, LiMn₂O₄ does suffer from a critical problem: it is unstable in the presence of electrolytes and suffers from capacity degradation during cycling. This seriously limits the practical applications of an otherwise very promising material.

Ying Wang and his co-workers used atomic layer deposition (ALD) to deposit the Al₂O₃ coating on LiMn₂O₄ cathodes. This method allows fine control over the thickness and conformation of the thin films, and allowed the group to create ultra-thin coatings on the cathodes. Theses ‘nano-coated’ cathodes were then compared with bare cathodes to study differences in electrochemical performance. The group discovered that the Al₂O₃ coating reduced dissolution of manganese ions from the cathode into the electrolyte, and also reduced decomposition of the electrolyte at the cathode surface. This resulted in a significantly enhanced cycling performance of the LiMn2O4 cathode.

To read more about this study, click here.

New Nanoscale Communication

Polyethylenimine–carbon nanotube nanohybrids for siRNA-mediated gene silencing at cellular level

Stéphanie Foillarda, Guy Zuber and Eric Doris

Nanoscale DOI:10.1039/C0NR01005G

Carbon nanotube (CNT) based structures which can act as ‘nanohybrid vehicles’ for the delivery of functional molecules into cells have been developed by scientists in France.

Synthetic interfering RNA (siRNA) is able to inhibit the expression of a targeted gene by triggering enzymatic and sequence-selective degradation of the corresponding mRNAs, which holds great promise for the highly selective treatment of medical disorders at a genetic level. However, nucleic acids require a ‘delivery vehicle’ to take carry them through the cellular membrane and to the sites where they are required. The CNT hybrid nanostructure developed by this group is intended to do exactly this.

Eric Doris and co-workers at CEA, Service de Chimie Bioorganique et de Marquage, covalently modified short CNTs (~200 nm) with the cationic polymer polyethylenimine (PEI), which were then able to bind siRNA. The intention was to build a nanostructure which could enter cells by endocytosis but escape endosomal capture to increase the biological activity of the payload. They appear to be successful in this as they show that their system performs better than a reference lipid carrier.

To read this article, click here.

New Nanoscale Feature Article

Surfactant-assisted, shape-controlled synthesis of gold nanocrystals

Junyan Xiao and Limin Qi

Nanoscale, DOI: 10.1039/c0nr00814a

This week at Nanoscale we have a published a Feature Article on the shape control of gold nanoparticles using surfactant systems. In this work, the authors Junyan Xiao and Limin Qi provide a comprehensive review of the techniques used to grow anisotropic gold nanoparticles, starting with an overview of the general strategies, before delving deeper into the role of surfactants in the production of some truly remarkable nanostructures. The descriptions of the various growth mechanisms are accompanied by excellent schematic diagrams which provide a valuable insight into the complexities of crystal formation and growth.

It is well known that gold nanoparticles have many unique chemical and physical properties, and there is much interest in applying them in a wide range of exciting applications. For example, they have been studied for use in nanoelectronics, drug delivery, catalysis, sensing, and photothermal therapy, to name but a few. Importantly, they exhibit particularly strong absorption and scattering of light due to localized surface plasmon resonance, a property which will be harnessed in the development of some revolutionary bioimaging devices. However, if these potential applications are to be realized, the growth of gold nanoparticles needs to be highly controlled in order exploit different properties which arise as we change their size, shape and surface chemistry.

Surfactants are vital in nanoparticle synthesis. Not only do they provide a protective capping layer and a means of conjugation, but they play an active role in particle nucleation and growth. Therefore, the choice of surfactant, or the design of a surfactant system, is crucial. In this review, the authors focus on gold nanocrystal synthesis assisted by single surfactants, mixed surfactants, supramolecular surfactants, as well as metal–surfactant complex templates.

To read this article, click here.