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Zhongwei Chen, a chemical engineering professor at Waterloo, and a team of graduate students have created a low-cost battery using silicon that boosts the performance and life of lithium-ion batteries. Their findings are published in the latest issue of Nature Communications. Waterloo's silicon battery technology promises a 40 to 60 per cent increase in energy density, which is important for consumers with smartphones, smart homes and smart wearables. The environmentally safe technology could also make dramatic improvements for hybrid and electric vehicles. The findings could mean an electric car may be driven up to 500 kilometres between charges and the smaller, lighter batteries may significantly reduce the overall weight of vehicles. Current lithium-ion batteries normally use graphite anodes. The Waterloo engineers found that silicon anode materials have a much higher capacity for lithium and are capable of producing batteries with almost 10 times more energy. "Graphite has long been used to build the negative electrodes in lithium-ion batteries," said Professor Chen, the Canada Research Chair in Advanced Materials for Clean Energy and a member of the Waterloo Institute for Nanotechnology and the Waterloo Institute for Sustainable Energy. "But as batteries improve, graphite is slowly becoming a performance bottleneck because of the limited amount of energy that it can store." The most critical challenge the Waterloo researchers faced when they began producing batteries using silicon was the loss of energy that occurs when silicon contracts and then expands by as much as 300 per cent with each charge cycle. The resulting increase and decrease in silicon volume forms cracks that reduce battery performance, create short circuits, and eventually cause the battery to stop operating. To overcome this problem, Professor Chen's team along with the General Motors Global Research and Development Centre developed a flash heat treatment for fabricated silicon-based lithium-ion electrodes that minimizes volume expansion while boosting the performance and cycle capability of lithium-ion batteries. "The economical flash heat treatment creates uniquely structured silicon anode materials that deliver extended cycle life to more than 2000 cycles with increased energy capacity of the battery," said Professor Chen. Professor Chen expects to commercialize this technology and expects to see new batteries on the market within the next year. Explore further: New battery technologies take on lithium-ion More information: Fathy M. Hassan et al. Evidence of covalent synergy in silicon–sulfur–graphene yielding highly efficient and long-life lithium-ion batteries, Nature Communications (2015). DOI: 10.1038/ncomms9597

Zhang X.,Waterloo Institute for Nanotechnology | Zhang X.,University of Waterloo | Servos M.R.,University of Waterloo | Liu J.,Waterloo Institute for Nanotechnology
Langmuir | Year: 2012

Single-stranded DNA can be adsorbed by citrate capped gold nanoparticles (AuNPs), resulting in increased AuNP stability, which forms the basis of a number of biochemical and analytical applications, but the fundamental interaction of this adsorption reaction remains unclear. In this study, we measured DNA adsorption kinetics, capacity, and isotherms, demonstrating that the adsorption process is governed by electrostatic forces. The charge repulsion among DNA strands and between DNA and AuNPs can be reduced by adding salt, reducing pH or by using noncharged peptide nucleic acid (PNA). Langmuir adsorption isotherms are obtained, indicating the presence of both adsorption and desorption of DNA from AuNPs. While increasing salt concentration facilitates DNA adsorption, the desorption rate is also enhanced in higher salt due to DNA compaction. DNA adsorption capacity is determined by DNA oligomer length, DNA concentration, and salt. Previous studies indicated faster adsorption of short DNA oligomers by AuNPs, we find that once adsorbed, longer DNAs are much more effective in protecting AuNPs from aggregation. DNA adsorption is also facilitated by using low pH buffers and high alcohol concentrations. A model based on electrostatic repulsion on AuNPs is proposed to rationalize the DNA adsorption/desorption behavior. © 2012 American Chemical Society. Source

Saran R.,Waterloo Institute for Nanotechnology | Liu J.,Waterloo Institute for Nanotechnology
Inorganic Chemistry Frontiers | Year: 2016

Pb2+ is a very important metal cofactor in DNAzyme catalysis. GR5 is the first reported DNAzyme, and 17E is the most thoroughly studied. Both have the highest activity with Pb2+ and are by far the fastest RNA-cleaving DNAzymes. GR5 reacts only with Pb2+ while 17E is also active with a number of other divalent metal ions. It is also interesting to note that Pb2+ shows activity with most RNA-cleaving DNAzymes. To understand these Pb2+-dependent DNAzymes and the occurrence of DNAzyme sequences, herein systematic mutation studies are performed on GR5. A comparison with 17E is also made. The A6, G7, C13, and G14 positions in 17E have been previously established to be crucial and we report A6, G7, C14, and G15 in GR5 to have the same role. The guanine at the cleavage site dinucleotide junction of the substrate strand is also mutated to hypoxanthine, 2-aminopurine, and adenine. Again, both enzymes show the same trend of activity change. Our results suggest that both DNAzymes have a similar binding pocket for Pb2+. The reason for Pb2+ being active in many DNAzymes is attributed to its simple binding motif requirement. Finally, we propose that 17E is a special form of GR5. They both have the simple sequence requirements needed for Pb2+-dependent activity, but 17E has additional motifs making it active also with other divalent metal ions. © the Partner Organisations 2016. Source

Khoshnegar M.,Institute for Quantum Computing | Khoshnegar M.,Waterloo Institute for Nanotechnology | Majedi A.H.,Harvard University | Majedi A.H.,Institute for Quantum Computing | Majedi A.H.,Waterloo Institute for Nanotechnology
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The electronic properties of single and few particles in core-shell nanowire quantum dots (NWQDs) are investigated. By performing configuration-interaction (CI) calculations we particularly elucidate how elevated symmetry character (C3v or D2d) exhibited by single-particle orbitals enhances the phase coherence of exciton-photon wave function though suppressing spin-flip processes. Detailed calculations presented here demonstrate how strain-induced potentials manipulate the symmetry characters, intrinsic oscillator strength, and electron-hole dipole in NWQDs. An orbital-dependent kinetic energy is defined based on single-particle dispersion and orbital spreadout in k space. It is shown that the exchange occurring between this kinetic energy and strain-induced potentials is responsible for orbital distortions, and thus the energy reordering of different direct and correlation terms. Various structures have been examined to elaborate on the influence of size and orientation together with axial and lateral symmetry of NWQDs. Our many-body calculations suggest that binding energies of s-shell few-particle resonances X0± and XX0 are suppressed when axial and lateral localizations become comparable. Then exerting an external perturbation may renormalize the binding energies, realizing a transition from the antibinding to the binding regime or vice versa. In this regard, we specifically show that kinetic energy of single particles, and thus correlation energies of associated complexes, exposed to an electric field remain relatively unaffected and the interplay between direct Coulomb terms reorders the multiexcitonic resonances. Sub-μeV fine structure splitting along with the tunable XX0 binding energy offers NWQDs promising for generating entangled photons in both regular and time-reordering schemes. © 2012 American Physical Society. Source

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While lithium-ion batteries are currently the gold standard for batteries and used in most of our electronics -- smartphones, computers, and more -- they have their short-comings. Compared to other battery technologies being tested in labs, they're not the best when it comes to energy storage capacity and lifetime length. Researchers around the world are looking for the better battery that can store more energy, weigh less and last longer than traditional lithium-ion batteries. While many researchers have been working on entirely different battery technologies, researchers at the University of Waterloo decided to address the shortcomings of the lithium-ion battery head-on. The researchers decided to focus on the negative anode of li-on batteries, usually made from graphite. “Graphite has long been used to build the negative electrodes in lithium-ion batteries,” said Professor Chen, the Canada Research Chair in Advanced Materials for Clean Energy and a member of the Waterloo Institute for Nanotechnology and the Waterloo Institute for Sustainable Energy. “But as batteries improve, graphite is slowly becoming a performance bottleneck because of the limited amount of energy that it can store.” Using graphite, the maximum theoretical capacity of the battery is 370 mAh/g (milliamp hours per gram), but silicon has a theoretical capacity of 4,200 mAh/g. Silicon also has the added benefit of being much cheaper. So, why hasn't silicon been used already? The problem with silicon is that it interacts with the lithium inside the cell during the charge cycle and expands and contracts as much as 300 percent. That expansion causes cracks and ultimately causes the battery to fail. The research team figured out a way to minimize the expansion by using a flash heat treatment for the silicon electrodes that creates a "robust nanostructure." This structure resulted in less contact between the electrode and the lithium which cut out most of the expansion and contraction and made the battery much more stable. The new design had a capacity of than 1,000 mAh/g over 2,275 cycles and the researchers say that the design promises a 40 to 60 percent increase in energy density over traditional lithium-ion batteries. That means that an electric car with this new battery design could have a range of over 300 miles, while the batteries themselves would be lighter, reducing the overall weight of the vehicle. The team is working on commercializing the new design and hope that it will be in new batteries in the next year.

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