Lithium ion battery for electronic textiles grows back together after breaking
Electronics that can be embedded in clothing are a growing trend. However, power sources remain a problem. In the journal Angewandte Chemie, scientists have now introduced thin, flexible, lithium ion batteries with self-healing properties that can be safely worn on the body. Even after completely breaking apart, the battery can grow back together without significant impact on its electrochemical properties.
Existing lithium ion batteries for wearable electronics can be bent and rolled up without any problems, but can break when they are twisted too far or accidentally stepped on–which can happen often when being worn. This damage not only causes the battery to fail, it can also cause a safety problem: Flammable, toxic, or corrosive gases or liquids may leak out.
A team led by Yonggang Wang and Huisheng Peng has now developed a new family of lithium ion batteries that can overcome such accidents thanks to their amazing self-healing powers. In order for a complicated object like a battery to be made self-healing, all of its individual components must also be self-healing. The scientists from Fudan University (Shanghai, China), the Samsung Advanced Institute of Technology (South Korea), and the Samsung R&D Institute China, have now been able to accomplish this.
The electrodes in these batteries consist of layers of parallel carbon nanotubes. Between the layers, the scientists embedded the necessary lithium compounds in nanoparticle form (LiMn(2)O(4) for one electrode, LiTi(2)(PO(4))(3) for the other). In contrast to conventional lithium ion batteries, the lithium compounds cannot leak out of the electrodes, either while in use or after a break. The thin layer electrodes are each fixed on a substrate of self-healing polymer. Between the electrodes is a novel, solvent-free electrolyte made from a cellulose-based gel with an aqueous lithium sulfate solution embedded in it. This gel electrolyte also serves as a separation layer between the electrodes.
After a break, it is only necessary to press the broken ends together for a few seconds for them to grow back together. Both the self-healing polymer and the carbon nanotubes “stick” back together perfectly. The parallel arrangement of the nanotubes allows them to come together much better than layers of disordered carbon nanotubes. The electrolyte also poses no problems. Whereas conventional electrolytes decompose immediately upon exposure to air, the new gel is stable. Free of organic solvents, it is neither flammable nor toxic, making it safe for this application.
The capacity and charging/discharging properties of a battery “armband” placed around a doll’s elbow were maintained, even after repeated break/self-healing cycles.
One team has already made a cat ‘disappear’ with a device that has huge military potential
Mainland scientists are increasingly confident of developing the world’s first invisibility cloak, using technology to hide objects from view and make them “disappear”.
The central government has funded at least 40 research teams over the past three years to develop the idea, which until now has largely been the stuff of science fiction and fantasy novels like the Harry Potter series.
The technology would have obvious military uses such as developing stealth aircraft, but Beijing believes the research could lead to wider technological breakthroughs with broader uses, scientists involved in the research said. The teams involved include researchers at Tsinghua University and the Chinese Academy of Sciences.
The main approaches are developing materials that guide light away from an object, creating electromagnetic fields to bend light away from what one is trying to hide and copying nature to make hi-tech camouflage materials.
A team of Chinese scientists evaluates the impact of a website based on the interaction between its users with the entire Web
A new study shows that small websites, in terms of daily user flux based on number of clicks, have a disproportionally high impact when it comes to traffic generation and influence compared to larger websites. These findings, about to be published in EPJB, have implications for estimating the value of sites and related advertising revenue. They result from the work of Lingfei Wu from the City University of Hong Kong and Jiang Zhang from the School of Management, at Beijing Normal University, China.
Previous studies have analysed hyperlinks, while individual browsing records provide insight for understanding local surfing behaviour. However, they fail to provide information on more internet-wide collective browsing behaviour. Hence, to understand the complex interactions between websites, it is necessary to analyse the transportation of traffic, referred to as the flow of clickstreams between websites.
In this study, the authors analyse the clickstream networks composed of the 1,000 most popular websites. They rely on models of clickstream networks based on so-called Markov matrices. They then validate their findings through network flow analysis, tracking users’ movement.
Wu and Zhang found that the accessibility of websites in the clickstream network increases more slowly than the level of traffic for the sites studied. Unlike previously thought, this study based on clickstreams reveals that the web is not solely dominated by a few hubs. And relatively small sites have a greater chance of acquiring popularity than larger ones.