The world of rechargeable batteries is full of trade-offs. While lithium-ion (Li-ion) batteries are currently the most commercially successful, their low energy density doesn't allow for a long driving range. They are also very expensive, often accounting for half the price of electric vehicles. One alternative is lithium-sulfur (Li-S) batteries, which are attractive for their high gravimetric energy density that allows them to store more energy than Li-ion batteries. And although they still use some lithium, the sulfur component allows them to be much cheaper than Li-ion batteries. But one of the biggest drawbacks of Li-S batteries is their short cycle life, which causes them to lose much of their capacity every time they are recharged.
Now a team of researchers led by Yi Cui, a professor of materials science and engineering at Stanford University, has developed a Li-S battery that can retain more than 80% of its 1180 mAh/g capacity over 300 cycles, with the potential for similar capacity retention over thousands of cycles. In contrast, most Li-S batteries lose much of their capacity after a few tens of cycles. To achieve this improvement, the researchers first identified a new mechanism that causes capacity decay in Li-S batteries after cycling. In order for a Li-S battery to successfully recharge, the lithium sulfide in the cathode must be bound to the cathode surface—in this case, the inner surface of the hollow carbon nanofiber that encapsulates it. This binding creates a good electrical contact to allow for charge flow. But the researchers found that, during the discharge process, the lithium sulfide detaches from the carbon, resulting in a loss of electrical contact that prevents the battery from fully recharging.
After identifying the problem, the researchers set about fixing it by adding polymers to the carbon nanofiber surface in order to modify the carbon-sulfur interface. The polymers are amphiphilic, meaning they are both hydrophilic (water-loving) and lipophilic (fat-loving), similar to soap. This property gives the polymers anchoring points that allow the lithium sulfides to bind strongly with the carbon surface in order to maintain strong electrical contacts. As experiments showed, sulfur cathodes containing the amphiphilic polymers had very stable performance, with less than 3% capacity decay over the first 100 cycles, and less than 20% decay for more than 300 cycles. Although the improvement is a big step forward, the capacity retention still doesn't compare to Li-ion batteries, some of which have lifespans approaching 10,000 cycles. In order to avoid having to replace the battery every few years, electric vehicles require these longer lifespans. But Cui says that Li-S batteries have the potential to close this gap in the foreseeable future. "Using the amphiphilic polymer idea here in this paper, together with nanoscale materials design and synthesis, it is possible to improve the cycle life up to 10,000 cycles," Cui told Phys.org. "My group is working on this. Our recent results on nanomaterials design already improved to 1000 cycles." In the future, Cui think Li-S batteries will give Li-ion batteries some serious competition. "The Li-S batteries become pretty promising for electric vehicles," he said. "The life cycle needs to improve further. The lithium metal anodes' safety problem needs to be solved. It is possible to get around Li metal anodes with Si anodes."
On three different occasions, the candidate with the most votes didn't become President of the United States. We call this "The Electoral College Problem." Here a solution. Simple. Mathematical. Rational.
Free travel tip and photos from all over the world...
This map is not a professionally produced map and that is the beauty of this website. Virtually anyone can make a 1-feature world map by simply clicking on a checklist all of the countries you want highlighted on your map. Second, open the file and add some text and a few lines to label it. This took less than 20 minutes to make with no need for any cartographic or GIS experience (this PNG didn't compress well, the full image of this map can be seen here).
Robin Good: If you are looking for online resources where to find free / creative-commons licensed songs and music tracks for your presentation or video clip here is a good collection of 20 such resources.
Find out how the Pilgrims and the Wampanoag Native Americans celebrated the first Thanksgiving together at Plymouth Plantation.
Thanksgiving is right around the corner and this is a great resource with videos, primary documents, virtual field trips and lesson plans for all grades, K-12. Students can see aspects of lifestyles, housing types and economic activies of both the Pilgrims and the Wampanoags. For more resources about the Mayflower and the historically re-enacted village, see the Plimoth Plantation website.
If you're short on time but looking to learn about some of the coolest and most engaging web 2.0 tools, you're in luck! From Today's Meet to Socrative, there's plenty here for a teacher on the go but in the know.
Having just freshened our own website, we felt it was timely to repost our 10 Commandments of About Us pages. Need a PDF to share with decision-makers at your organization? Glad to oblige. Commandment 1: Know thy ...
Blubbr is a neat quiz creation service that I recently learned about on Danny Nicholson's blog. Using Blubbr you can create interactive quizzes that are based on YouTube clips. Your quizzes can be about anything of your choosing. The structure of the quizzes has a viewer watch a short clip then answer a multiple choice question about the clip. Viewers know right away if they chose the correct answer or not.
Although these were designed specifically for GIS day during Geography Awareness Week, these 2 excellent map-based treasure hunts from ESRI are great any time of year. The answer to the question will only pop up in you are zoomed in the the right region (SHIFT + Make a box = Zoom to area). These links will take you to the World Cities quiz and also to the Mountains quiz.
From Karen: Ooohhh ooooohh oooooohh -- this looks like a fabulous and fun tool for biz storytelling!! Now you can make your stories interactive. How fun is that?!!
I'll play with this tool this afternoon while avoiding all the shopping frenzy of Black Friday. Hope you have fun with it too and that it really helps connect with customers and build your business!
Thanks go to fellow curator Baiba Svenca for finding and sharing this post.
inklewriter is a free tool designed to allow anyone to write and publish interactive stories. It’s perfect for writers who want to try out interactivity, but also for teachers and students looking to mix computer skills and creative writing.
From simple charts to complex maps and infographics, Brian Suda's round-up of the best – and mostly free – tools has everything you need to bring your data to life. A common question is how to get started with data visualisations. Beyond following blogs, you need to practice – and to practice, you need to understand the tools available. In this article, get introduced to 20 different tools for creating visualisations.