Time filter

Source Type

Chesapeake, VA, United States

See K.A.,University of California at Santa Barbara | Jun Y.-S.,University of California at Santa Barbara | Gerbec J.A.,University of California at Santa Barbara | Gerbec J.A.,Mitsubishi Chemical United States Inc. | And 4 more authors.
ACS Applied Materials and Interfaces | Year: 2014

The Li-S system offers a tantalizing battery for electric vehicles and renewable energy storage due to its high theoretical capacity of 1675 mAh g -1 and its employment of abundant and available materials. One major challenge in this system stems from the formation of soluble polysulfides during the reduction of S8, the active cathode material, during discharge. The ability to deploy this system hinges on the ability to control the behavior of these polysulfides by containing them in the cathode and allowing for further redox. Here, we exploit the high surface areas and good electrical conductivity of mesoporous carbons (MC) to achieve high sulfur utilization while functionalizing the MC with sulfur (S-MC) in order to modify the surface chemistry and attract polysulfides to the carbon material. S-MC materials show enhanced capacity and cyclability trending as a function of sulfur functionality, specifically a 50% enhancement in discharge capacity is observed at high cycles (60-100 cycles). Impedance spectroscopy suggests that the S-MC materials exhibit a lower charge-transfer resistance compared with MC materials which allows for more efficient electrochemistry with species in solution at the cathode. Isothermal titration calorimetry shows that the change in surface chemistry from unfunctionalized to S-functionalized carbons results in an increased affinity of the polysulfide intermediates for the S-MC materials, which is the likely cause for enhanced cyclability. © 2014 American Chemical Society.

Handa N.V.,University of California at Santa Barbara | Li S.,University of California at Santa Barbara | Gerbec J.A.,University of California at Santa Barbara | Gerbec J.A.,Mitsubishi Chemical United States Inc. | And 4 more authors.
Journal of the American Chemical Society | Year: 2016

We have developed an efficient synthetic platform for the preparation of a new class of high performance thermosets based on the 1,3-dipolar cycloaddition of a bifunctional sydnone with a trifunctional alkyne. These processable materials possess outstanding thermal stability, with Td5% of 520 °C and a weight loss of <0.1% per day at 225 °C (both in air). Key to this performance is the stability of the starting functional groups that allows for reactive B-staging via simple thermal activation to give fully aromatic and highly cross-linked polypyrazole-based thermosets. © 2016 American Chemical Society.

Chiu C.-Y.,University of California at Santa Barbara | Wang H.,Mitsubishi Chemical United States Inc. | Phan H.,University of California at Santa Barbara | Shiratori K.,Synergy Inc. | And 2 more authors.
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2016

A series of polymers based on 8,8′-biindeno[2,1-b]thiophenylidene for use in photovoltaic devices and field-effect transistors are reported. These structurally twisted olefins are effective building blocks for preparation of low bandgap polymers with optical bandgaps of 1.2-1.5 eV. Device performance, such as Voc and Jsc, in solar cell devices could be successfully modulated by incorporation of a variety of comonomers. Ambipolar properties in field-effect transistors using Au electrodes were also studied, with PtBTPDPP exhibiting balanced charge transport properties with hole and electron mobilities of 0.09 and 0.12 cm2·V-1·s-1, respectively. © 2015 Wiley Periodicals, Inc.

Tasaki K.,Mitsubishi Chemical United States Inc.
Journal of Physical Chemistry C | Year: 2014

The structures and energetics of a number of graphite intercalation compounds (GICs) having a relatively wide range of chemistry have been investigated by density functional theory calculations with the van der Waals correction using the dispersion correction method within the framework of generalized gradient approximation. The GICs studied included potassium-intercalated graphite (KCn), lithium-intercalated graphite (LiCn), lithium solvated by dimethyl sulfone (DMSO)-intercalated graphite (Li(DMSO)4Cn), lithium solvated by dibuthoxy ethane (DBE)-intercalated graphite (Li(DBE)2Cn), perchlorate (ClO4)-intercalated graphite (ClO4C n), and hexafluorophosphate (PF6)-intercalated graphite (PF6Cn). Our calculations show reasonable agreement with experimental data for the interlayer distances of the GICs. A correlation between the size of the intercalate and the interlayer distance of the GIC has been observed. Our study has also predicted that all the GICs studied here are energetically stable except for Li(DBE)2Cn, consistent with experimental observations. Our results have suggested that there is a strong correlation between the intercalation energy and the electron transfer between the intercalate and graphite. On the basis of our results, we propose that the ionization potential or the electron affinity of the intercalate, along with the size of the intercalate, is a good measure for the stability of the resulting GIC in general. © 2013 American Chemical Society.

Kim K.H.,Korea Advanced Institute of Science and Technology | Kim K.H.,University of California at Santa Barbara | Jun Y.-S.,University of California at Santa Barbara | Gerbec J.A.,Mitsubishi Chemical United States Inc. | And 3 more authors.
Carbon | Year: 2014

The lithium-sulfur (Li-S) system is an attractive candidate to replace the current state-of-the-art lithium-ion battery due to the promising theoretical charge capacity of 1675 mA h/g and energy density of 2500 Wh/kg; however, the dissolution of intermediate polysulfides into the organic liquid electrolyte during cycling hinders its practical realization. We report the synthesis of mesoporous graphene-silica composite (m-GS) as a supporting material of sulfur for Li-S batteries. The ordered porous silica structure was synthesized parallel to functionalized graphene sheets (FGSs) through the ternary cooperative assembly of the graphene, silica, and block copolymer precursors. The well-defined, unique mesoporous structure integrates the electronic conductivity of graphene and the dual functions of silica as a structure building block and in situ polysulfide ab-/ad-sorbing agent to give a Li-S battery that has both good retention ability of polysulfides and good rate capability. © 2013 Elsevier Ltd. All rights reserved.

Discover hidden collaborations