![\"Three](\"http:\/\/cafe.foundation\/blog\/wp-content\/uploads\/2016\/01\/lithium-sulfur-doping-process.jpg\")
<\/a>Three steps in making doped, crumpled cathodes<\/p><\/div>\n
Researchers synthesized \u201chighly crumpled\u201d nitrogen-doped graphene (NG) sheets with \u201cultrahigh pore volume\u201d and large surface area (1,158 square meters\u2013 about 12,465 square feet or about one-third the area of a football field) per gram<\/em>.\u00a0 This large area and high porosity \u201cenable strong polysulfide adsorption and high sulfur content for use as a cathode material in Li-sulfur batteries.\u201d\u00a0 Interwoven rather than stacked, the wrinkled material provides ample room for \u201cnitrogen-containing active sites.\u201d<\/p>\n The batteries, according to the researchers, \u201cachieved\u201d a high capacity of 1,226 milliamp-hours per gram and 75-percent capacity retention after 300 cycles.\u00a0 This demonstrated capacity and longevity is something other experimenters with lithium sulfur batteries have tried unsuccessfully to achieve.<\/p>\n Green Car Reports<\/em> quotes Jiangxuan Song<\/a>, one of the researchers on the techniques used. \u201cLithium\u2013sulfur battery cells using these wrinkled graphene sheets as both sulfur host and interlayer achieved a high capacity of 1227 mAh\/g and long cycle life (75% capacity retention after 300 cycles) even at high sulfur content (\u226580 wt %) and sulfur loading (5 mg sulfur\/cm2). A high capacity of 1082 mAh\/g was still achieved with an ultrahigh sulfur content of 90 wt %, and a capacity of 832 mAh\/g was retained after 200 cycles. Areal capacity was 5 mAh\/cm2. A paper on their work is published in the ACS journal\u00a0Nano Letters.\u201d<\/p>\n Nitrogen-doping the graphene in the cathode apparently improves the electrochemical performance and helps yield the results shown above.\u00a0 Such doping improves otherwise lackluster conductivity and leads to better energy density, cycling stability and Coulombic efficiency.\u00a0 The process deposits nitrogen in the lattice-work-like structure of the graphene and depending on the amount of nitrogen deposited, makes a positive change in the material\u2019s characteristics.<\/p>\n Penn State researchers think this can be applied to supercapacitors with the hope of similar performance improvements.<\/p>\n Why Lithium Sulfur?<\/strong><\/p>\n Next to Lithium-air, Lithium-sulfur offers greatest potential energy density<\/p><\/div>\n Lithium sulfur (Li-S) are, with current technology, the most likely successor to lithium-ion batteries<\/a>. Penn States\u2019 approach might help overcome Li-S battery\u2019s poor cycle stability and low rates, and seem to show, in this instance significant performance improvements.<\/p>\n Comparison between Li-ion and Li-S batteries shows much greater theoretical energy density<\/p><\/div>\n Energy Technologies Area (ETA) at Berkeley<\/a> state that lithium-sulfur batteries have a very high theoretical specific energy (2,680 Wh\/kg), much higher than that of the best Li-ion cell (~580 Wh\/kg). \u201cThanks to this high energy per weight, Li\/S batteries could store more energy, and therefore, provide greater vehicle range as well as longer operating times in all applications.<\/p>\n \u2018Sulfur is inexpensive, non-toxic, safe, and environmentally benign, so Li\/S batteries would be cheaper than current Li-ion batteries, and they would be less prone to safety problems that have plagued some of today’s Li-ion batteries, such as overheating and catching fire.\u201d<\/p>\n These pluses, coupled with developments at Penn State, might make lithium-sulfur batteries a plausible route to take for the near future.<\/p>\n You can find the complete text for the research team’s paper in Nano Letters<\/em> (for a fee)<\/a>, or in .pdf form for free<\/a>.<\/p>\n<\/a><\/a>