Tech Highlights

Tech HighlightsECS journals was prepared by Colm Glynn and David McNulty of University College Cork, Ireland, David Enos of Sandia National Laboratories, Zenghe Liu of Verily Life Science, and Donald Pile of Rolled-Ribbon Battery Company. Each article highlighted here is available free online.

Performance of Three-Dimensional LiMn2O4/Carbon Composite Cathodes Prepared Via Sol-Gel Impregnation

With the ever advancing improvements in electronics and display technologies, it is crucial that Li-ion batteries are able to rise to the challenge of powering next generation consumer electronics. Consequently, the development of electrode materials for Li-ion batteries that are capable of delivering high capacities with stable capacity retention is of the utmost importance. Researchers from the University of Bremen have investigated the fabrication of 3D composite cathodes consisting of LiMn2O4 particles deposited directly onto an electrically conductive matrix of carbon fibres via sol-gel impregnation. The electrochemical performance of the composite cathodes was evaluated as a function of the number of sol impregnation steps. Through systematic galvanostatic cycling, the researchers determined that high capacity cathodes could be obtained from increased filling of the carbon matrix with the LMO sol. A cathode sample after four filling cycles demonstrated a discharge capacity of 132mAh g-1 after 50 cycles, corresponding to ~89% of the theoretical capacity of LiMn2O4.

Additionally, as a proof-of-concept, LMO cathodes were cycled against Lithium Titanate (LTO) anodes in a solid state battery (SSB) setup. The evaluation of these cells offers valuable insight for future SSB applications.

From: I. Bardenhagen, J. Glenneberg, F. Langer, et al., J. Electrochem. Soc., 163, A2539 (2016).

Structure and Corrosion Performance of a Non-Chromium Process (NCP) Zr/Zn Pretreatment Conversion

Coating on Aluminum Alloys Chromate conversion coatings have long been the standard for the protection of aluminum alloys in marine applications. Due to the toxicity of chromate, industry is being pushed away from these chemistries to chromate-free replacements, such as non-chromated process (NCP) and trivalent chromium process (TCP) chemistries, developed by the Naval Air Systems Command (NAVAIR). In this work, a laboratory-produced NCP coating was benchmarked against a commercially available TCP coating. Under immersion conditions, NCP was found to ennoble the open circuit and pitting potentials, increase the polarization resistance by an order of magnitude, and suppress the anodic activity of an AA2024 substrate, indicating that it functioned primarily as an anodic inhibitor.

However, for neutral salt fog exposure and aggressive beach exposure, the NCP was found to be less effective, exhibiting a higher dissolution rate than that achieved with a TCP coating, and an inability to prevent galvanic attack when coupled to a stainless steel fastener. The ineffectiveness in inhibiting corrosion under such aggressive conditions was attributed to the composition of the NCP film, which is a combination of Zr(OH)2 and Zn(OH)2, both of which are more soluble, and the NCP film’s lower adhesion strength than that of Cr(OH)3 that makes up the TCP coating.

From: L. Li, B. W. Whitman, C. A. Munson, et al., J. Electrochem. Soc.,163, C718 (2016).

Triple-Switchable Biosensors and an AND Logic Gate Based on Binary Assembly of weak Polyelectrolyte Multilayers and Hydrogel Films

Switchable electrode interfaces responsive to physical, chemical, or biological signals have attracted immense research interest during the last decade because of their potential applications in biosensors and bioelectronics. An example of such interfaces was recently reported by a group of researchers from several universities and institutes in China. On the surface of pyrolytic graphite electrodes, the authors first assembled a polyelectrolyte film via layer-by-layer coating with poly(allylamine hydrochloride) and poly(acrylic acid). A second hydrogel film was then formed on top of the polyelectrolyte layer by radical polymerization of N,N-diethylacrylamide in the presence of horseradish peroxidase.

The resulting binary films exhibited clear and reversible on-off behavior towards pH, temperature, and sulfate concentration changes, as demonstrated by the electrode responses to K3Fe(CN)6. Similar behavior was observed when the electrodes were used to electrocatalytically reduce H2O2 with K3Fe(CN)6 as the mediator. The authors demonstrated that the pH-sensitivity of the system originated from the inner polyelectrolyte layer due to the presence of free amino and carboxyl groups, while the thermo- and salt-sensitivities were attributed to the structure change of the outer poly(N,N-diethylacrylamide) layer.

Finally, an AND logic gate was constructed with the three stimuli factors as the input and the electrode current as the output.

From: H. Yao, X. Luo, T. Yang, et al., J. Electrochem. Soc., 163, H1104 (2016).

Synthesis and Electrochromic Characterization of Graphene/V2O5/MoO3 Nanocomposite Films

Vanadium pentoxide, V2O5, is anelectrochromic material that, while possessing attractive properties, has some disadvantages that prevent it from being commercialized. Among these drawbacks are cycle reversibility and stability, and slow response rate. To address these drawbacks, researchers from China and Russia collaborated on a project developing a graphene/V2O5/MoO33 additions. The MoO3 addition lowered the potential difference between the anodic and cathodic peaks. Graphene was incorporated to improve the electrical conductivity, and thus increase the reversibility and the response rates. At the 50th cycle, decrease in charge density with cycling for the GVM film was approximately half that of the V film.

Both the coloration and bleaching times decreased below 1.5 s,from 1.6 s and 2 s, respectively, for the GVM film. Corresponding improvement in the measured optical modulation, the range in percent transmittance, was found for the GVM film (25%) compared to the V, VM, and GV films. These significant performance improvements for the GVM film are encouraging with respect to it becoming a fast-switching electrochromic material.

From: X. Ma, S. Lu, F. Wan, et al., ECS J. Solid State Sci. Technol., 5 , P572 (2016).

Demonstration of Direction Dependent Conduction through MoS2 Films Prepared by Tunable Mass Transport Fabrication

The range of applications for two dimensional (2D) materials are increasing due in part to the unique characteristics they exhibit compared to their bulk counterparts. The physical and optical properties of 2D transition metal dichalcogenides (TMDs) make them ideal for use as semiconductor layers in modern transistor technologies. Molybdenum disulfide (MoS2) is a notable TMD material due in part to its direct band gap when formed in a 2D structure. The deposition of defect-free long range 2D surfaces continues to be a challenge for transistor development and integration into existing processing methods. Belgian-based researchers have developed a facile method for the cost-effective deposition of large area MoS2 films through the sulfurization in H2S of thermally evaporated Mo layers.

Their paper, published in the JSS Focus Issue on Properties, Devices and Applications Based on 2D Layered Materials, demonstrates the important role played by interface roughness to the underlying substrate and mechanical stress during H2S treatments at varied pressures in determining the nature of the resulting film. The processes were optimized through mass transport smoothing to form MoS2 films that conformally coat the substrate. The techniques developed in this paper will be important for the low cost deposition of multifunctional MoS2 films for future device applications.

From: D. Chiappe, M. Mongillo, I. Asselberghs, et al., ECS J. Solid State Sci. Technol., 5, Q3046 (2016).

This article was originally published in Interface.

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