The specific capacity of commercially available cathode carbon-coated lithium iron phosphate is typically 120-160 mAh g À 1 , which is lower than the theoretical value 170 mAh g À 1 . Here we report that the carbon-coated lithium iron phosphate, surface-modified with 2 wt% of the electrochemically exfoliated graphene layers, is able to reach 208 mAh g À 1 in specific capacity. The excess capacity is attributed to the reversible reduction-oxidation reaction between the lithium ions of the electrolyte and the exfoliated graphene flakes, where the graphene flakes exhibit a capacity higher than 2,000 mAh g À 1 . The highly conductive graphene flakes wrapping around carbon-coated lithium iron phosphate also assist the electron migration during the charge/discharge processes, diminishing the irreversible capacity at the first cycle and leading to B100% coulombic efficiency without fading at various C-rates. Such a simple and scalable approach may also be applied to other cathode systems, boosting up the capacity for various Li batteries.

CitationBifunctional separator as a polysulfide mediator for highly stable Li-S batteries 2016 J. Graphical Abstract ABSTRACTThe shuttling process involving lithium polysulfides is one of the major factors responsible for the degradation in capacity of lithium-sulfur batteries (LSBs). Herein, we demonstrate a novel and simple strategy-using a bifunctional separator, prepared by spraying poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) on pristine separator-to obtain long-cycle LSBs. The negatively charged SO 3 -groups present in PSS act as an electrostatic shield for soluble lithium polysulfides through mutual coulombic repulsion, whereas PEDOT provides chemical interactions with insoluble polysulfides (Li 2 S, Li 2 S 2 ). The dual shielding effect can provide an efficient protection from the shuttling phenomenon by confining lithium polysulfides to the cathode side of the battery. Moreover, coating with PEDOT:PSS transforms the surface of the separator from hydrophobic to hydrophilic, thereby improving the electrochemical performance. We observed an ultralow decay of 0.0364% per cycle when we ran the battery for 1000 cycles at 0.25 C-far superior to that of the pristine separator and one of the lowest recorded values reported at a low current density. We examined the versatility of our separator by preparing a flexible battery that functioned well under various stress conditions; it displayed flawless performance. Accordingly, this economical and simple strategy appears to be an ideal platform for commercialization of LSBs.

A low-cost sensing mechanism of hydrogen gas is developed using polymer-derived ceramic, a liquid organic precursor, polysilazane with the addition of 5 wt% of photoinitiator, 2,2 Dimethoxy-2-phenyl acephenone. UV photopolymerization is utilized to partially cross-link the H-shaped free standing specimen, and then pyrolyzed at 1400°C in hot isostatic press under nitrogen gas to convert the partially cross-linked polymer into conducting and amorphous ceramic, silicon carbonitride. This work presents the preparation of free standing silicon carbonitride specimens as the sensor body for sensing hydrogen gas, depending on the semiconductive behavior of polymer-derived ceramics in high-temperature environments. The band gap of silicon carbonitride would be varied from adsorbing hydrogen molecules on the surface of the H-shaped free standing specimen with two different thicknesses. An amenable specimengeometry for the four-point test of measuring resistance is developed in a furnace filled with pure hydrogen and vacuumed environments.

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