factors, lithium-sulfur (Li-S) batteries are one of the most promising candidates for next-generation rechargeable batteries. Typical Li-S cells are assembled with an Li metal as the anode and active sulfur as the cathode with a separator and an electrolyte in between. Under cell discharging, lithium ions from the Li-metal anode travel across the cell and react with active sulfur to form Li polysulfi des (Li 2 S x , x = 4-8) in the active-sulfur cathode. Subsequently, the polysulfi de intermediates convert to the discharge product, lithium sulfi de (Li 2 S). Upon cell charging, lithium ions are plated back onto the anode while the Li 2 S converts back to S 8 . The overall electrochemical reaction (16Li + S 8 = 8Li 2 S) involves two electrons per sulfur. [ 2 ] Sulfur cathodes based on the S 0 ↔ S 2− electrochemical conversion have a high theoretical capacity (1672 mA h g −1 ). This cathode capacity is an order of magnitude higher than that of Li-insertion compound oxide cathodes used in the current Li-ion technology. [ 3 ] Coupled with the operating voltage of 2.15 V versus Li + /Li 0 , the theoretical energy density of Li-S batteries reaches 2600 W h kg −1 , a value which is 3-5 times higher than that of current commercial Li-ion batteries. [ 2,3 ] Further advantages of Li-S batteries include the relatively low cost of sulfur owing to its natural abundance and the relatively low ecological impact of sulfur due to its environmentally benign nature. [ 2,3 ] However, despite these promising attributes, the prototypical Li-S battery suffers from (i) the insulating nature of the active material and (ii) the diffusion of soluble polysulfi de intermediates. [ 3a-c , 4 ] The fi rst scientifi c challenge, the low electronic and ionic conductivity of the active material, causes poor redox accessibility and hence leads to low electrochemical utilization. [ 4d,e ] The second scientifi c challenge, the polysulfi de diffusion, results from the dissolution of the highly soluble polysulfi des into the liquid electrolyte currently used in Li-S batteries. Without effective constraints, the dissolved polysulfi des diffuse out readily from the cathode, penetrating through the separator and reacting detrimentally with the Limetal anode. [ 3c , 5 ] This is the main cause for the irreversible loss of the active material and for the unfavorable polysulfi de shuttle As a primary component in lithium-sulfur (Li-S) batteries, the separator may require a custom design in order to facilitate electrochemical stability and reversibility. Here, a custom separator with an activated carbon nanofi ber (ACNF)-fi lter coated onto a polypropylene membrane is presented. The entire confi guration is comprised of the ACNF fi lter arranged adjacent to the sulfur cathode so that it can fi lter out the freely migrating polysulfi des and suppress the severe polysulfi de diffusion. Four differently optimized ACNF-fi lter-coated separators have been developed with tunable micropores as an investigation into the electrochemical and engineering design param...

The majority of etching methods for synthesizing MXenes use water as the main solvent, which in turn limits direct use of MXenes in water-sensitive applications. In this work, we show that it is possible to etch, and delaminate, MXenes in the absence of water by using organic polar solvents and ammonium dihydrogen fluoride. We also demonstrate that electrodes made from Ti 3 C 2 T z etched in propylene carbonate, resulted in Na-ion battery anodes with double the capacity to those etched in water.

Free-standing porous carbon nanofiber interlayers with tunable surface area and pore structure have been studied to enhance the Li–S battery capacity and cycle life.

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Freestanding, binder-free supercapacitor electrodes based on high-purity polyaniline (PANI) nanofibers were fabricated via a single step electrospinning process. The successful electrospinning of nanofibers with an unprecedentedly high composition of PANI (93 wt %) was made possible due to blending ultrahigh molecular weight poly(ethylene oxide) (PEO) with PANI in solution to impart adequate chain entanglements, a critical requirement for electrospinning. To further enhance the conductivity and stability of the electrodes, a small concentration of carbon nanotubes (CNTs) was added to the PANI/PEO solution prior to electrospinning to generate PANI/CNT/PEO nanofibers (12 wt % CNTs). Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) porosimetry were conducted to characterize the external morphology of the nanofibers. The electrospun nanofibers were further probed by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The electroactivity of the freestanding PANI and PANI/CNT nanofiber electrodes was examined using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. Competitive specific capacitances of 308 and 385 F g(-1) were achieved for PANI and PANI-CNT based electrodes, respectively, at a current density of 0.5 A g(-1). Moreover, specific capacitance retentions of 70 and 81.4% were observed for PANI and PANI-CNT based electrodes, respectively, after 1000 cycles. The promising electrochemical performance of the fabricated electrodes, we believe, stems from the porous 3-D electrode structure characteristic of the nonwoven interconnected nanostructures. The interconnected nanofiber network facilitates efficient electron conduction while the inter- and intrafiber porosity enable excellent electrolyte penetration within the polymer matrix, allowing fast ion transport to the active sites.