Stephen C.T. Kwok

Enhanced cycle life of lead-acid battery using graphene as a sulfation suppression additive in negative active material

In this article, we report the addition of graphene (Gr) to negative active materials (NAM) of lead-acid batteries (LABs) for sulfation suppression and cycle-life extension. Our experimental results show that with an addition of only a fraction of a percent of Gr, the partial state of charge (PSoC) cycle life is significantly improved by more than 140% from 7078 to 17157 cycles. The particle size on a charged Pb-graphene (PbG) plate after the PSoC test is also found to be reduced by around 25% when compare with a Pb plate. Charge and discharge densities measurements from the cyclic voltammetry (CV) test show an enhancement with the addition of Gr, indicating an improvement in the reversibility reaction of PbSO4. An electrochemical model, which takes into account of reduced interfacial resistance, improved charge transfer and enhanced electroactive surface area, is proposed to elucidate the role of Gr throughout the course of a PSoC cycle test. It is demonstrated that experimental results are aligned with our proposed model with enhanced cycle life performance, where PbG plate maintains a higher electroactive surface area for adsorption and desorption of Pb2+ ions at the interface between active material and electrolyte occurs in parallel to reduced charge transfer.

Soft Mold Nanoimprint: Modeling and Simulation

Due to the shrinkage in size of many handheld electronic devices such as smartphones and laptop computers, packaging of a large number of components within a limited size chip becomes a challenging issue. Nanoimprint lithography (NIL) provides a low-cost solution in order to cope with the challenge. However, the de-molding process is very critical for determining the printing quality. The interaction between the mold and the substrate greatly affects the patterning result. Therefore it is necessary to understand the interaction between the nano-patterned mold and the substrate. This chapter introduces a multi-scale model by combining molecular dynamic (MD) simulation and a finite element analysis, which could predict the adhesion force between the nano-patterned mold and the polymer film substrate. It is suggested that a hydrophobic silane coating is necessary for reducing the adhesion force between the mold and the substrate leading to a successful printing result.

Electrochemical assembly and molecular dynamics simulation of SAM on copper for epoxy/copper adhesion improvement

This work reports on adhesion enhancement effects of self-assembled organothiol treatment on copper (Cu)/epoxy interface, as well as a significant reduction in treatment time under the influence of electric potential. The interfacial adhesion has 20-fold enhancement through the treatment due to improved linkage between copper substrate and epoxy layer by chemisorbed organothiol molecules. The treatment time was greatly reduced by a factor 32 from 16 hours to 30 minutes thanks to the electrical field assisted method without compromising the maximum adhesion strength, which was shown to be in order of 97.2Jm-2. Molecular Dynamics (MD) simulations were also carried out for studying the surface coverage effect of Self-assembly Monolayer (SAM) on Cu surface towards adhesion strength between Cuiepoxy interface. Simulation results together with experimental data were then used for explaining the adhesion promotion mechanism between Cu/epoxy interface.

Electrochemical assembly of SAM on copper for epoxy/copper adhesion improvement

This paper reports on adhesion enhancement effects of self-assembled organothiol treatment on copper/epoxy interface, as well as a significant reduction in treatment time by the electrochemical assembly approach. Interfacial adhesion strength between copper/epoxy interfaces was studied against different treatment time under the influence of electrical potential. A maximum 20-fold enhancement was demonstrated through improved chemical linkage formed between copper substrate and epoxy layer. The treatment time was also reduced by 32 times to 1800s with the proposed preparation method. Electrochemical characterization including electrochemical impedance spectroscopy (EIS) was carried out in this work. Results were correlated with adhesion enhancement effect by organothiol self-assembly monolayer (SAM). The double layer capacitance model was used to explain how molecular film formation process affects adhesion results between Cu/epoxy interfaces.

Potential-assisted assembly of thiol-based materials for reliable copper-epoxy interface

Despite the fact that copper has continuously being used as leadframe materials in electronic packaging, adhesion strength between copper-epoxy joint is prone to be weaken during reliability test. In order to solve this problem, thiol-based self-assembled material (SAM) is applied as coupling agent between copper and epoxy system. A remarkable interfacial adhesion improvement was reported by different groups [1–2]. This work reports on adhesion enhancement effects of self-assembled organothiol treatment on copper/epoxy interface, as well as a significant reduction in treatment time under the influence of electric potential. The interfacial adhesion has a maximum enhancement of 20-fold through the treatment due to improved linkage between copper substrate and epoxy layer by chemisorbed organothiol molecules. The treatment time was greatly reduced by 32 times to 1800s with the proposed preparation method and maximum adhesion strength up to 97.2±6.1 Jm−2 was demonstrated. The use of potential enhances preparation efficiency with adhesion improvement comparable to passive adsorption method make up in 16hrs.