bluuebunny/crossref_metadata_2025 huggingface dataset:
Wide Temperature Range Electrolyte Formulations for Start-Stop Vehicle Applications
Authors: Cheng Gang , Zhu Ye , Strand Dee
Published: February 2020

Over the last decade, many governments have implemented more stringent regulations on vehicle fuel economy and CO2 emissions. For example, European targets for new passenger cars reduce emissions to 130g CO2 per kilometer by 2015, with further reduction to 95g by 2021.   Start-stop vehicle engines, which shut off during stops for traffic or at a light, play an important role in achieving these targets. These vehicles require a battery with sufficient power to re-start the engine over a wide range of conditions and sufficient energy to run the lights, air conditioning, etc. on the vehicle when stopped.  

Lithium ion batteries are promising candidates to replace currently used lead acid batteries due to their high energy density as well as longer cycle life. However, the power performance of lithium ion batteries is limited at low temperatures required for automotive applications due to low conductivities of the electrolyte and the solid electrolyte interphase (SEI).  Solutions to the low temperature problem generally consist of adding solvents with very low melting points and/or low viscosity to the formulation which keep the formulation from freezing or reduce the viscosity at low temperature.  However, these solvents tend to be detrimental to high temperature stability, required to meet the lifetime requirements of the vehicle batteries. 

Wildcat has developed electrolyte formulations that improve the power performance at low temperature, but improve or maintain the high temperature stability relative to baseline electrolyte formulation.   Wide temperature range formulations were developed for both NMC//graphite and NMC//LTO electrode chemistries.
A Soluble-Lead-Redox-Flow-Battery with Embedded Reticulated Vitreous Carbon and Inter - Digitated Graphite As Negative and Positive Plates
Authors: Ravikumar Musuwathi Krishnamoorthy , Shukla Ashok Kumar
Published: February 2020

Characteristics of a 12 V soluble-lead redox flow battery (SLRFB) stack developed by employing reticulated vitreous carbon foam embedded into graphite plate  as negative flow fields and inter-digitated graphite plates as positive flow fields. The stack consists of 8 cells in series assembled with 7 bipolar plates, two monopolar plates and 8 spacers placed between each cell. The flow battery exhibits compelling Faradaic and voltage efficiencies at low current densities between 10 – 20 mAcm-2, and at charging-periods of 15-30 min. SLRFB exhibits an energy storage capacity of 50 – 60Wh and is able to deliver 100 W of constant power.  Long periods of constant – current  charging and higher current charging lead to a decrease in overall efficiency of the flow cell. The faradaic efficiency of SLRFB is 85% when it is charged for 15 min at 1A and is 65% when the charged for 3h. The faradaic efficiency decreases to 60% when the SLRFB is charged at 5A for 15 min. Long periods of constant current charge and discharge cycling lead to the accumulation of active materials specifically Pb and shedding of PbO2. A novel design to mitigate the aforesaid issues is highlighted and cycle – life data are presented.
Real-Time Crossover Measurement in All-Vanadium Redox Flow Batteries
Authors: Ashraf Gandomi Yasser , Aaron Douglas , Mench Matthew M.
Published: February 2020

Redox flow batteries have emerged as one of the most promising technologies for grid-scale energy storage options. Different chemistries have been developed, including the all-vanadium redox flow battery1. Among the different components of the all-vanadium redox flow batteries, the ion-exchange membrane plays a significant role via directly affecting the voltage and coulombic efficiencies. The ideal membrane must minimize resistance for proton flux and at the same time limit unwanted crossover of active species.

The species transport mechanism through the ion-exchange membrane has been the focus of several studies 2, 3. Also, different mathematical models have been developed to predict the transport through the membrane 4-8. However, experimental studies for the species transport through the ion-exchange membrane is rare 9, 10. In this talk, we will report on results of direct species crossover measurement through the ion-exchange membrane for the all-vanadium redox flow batteries. A unique test facility utilizing several test cells and UV-Vis spectrometry has been designed and verified that enables measurement of the species crossover with and without electric fields, so that individual driving forces of transport can be deconvoluted. The experimental data reveals the different crossover rates for individual vanadium oxide species as a function of concentration and electric field effect. 

1. M. Skyllas-Kazacos, M. Chakrabarti, S. Hajimolana, F. Mjalli, and M. Saleem, Journal of the Electrochemical Society, 158 (8), R55-R79 (2011).

2. A. Z. Weber and J. Newman, Journal of the Electrochemical Society, 150 (7), A1008-A1015 (2003).

3. Y. A. Gandomi and M. M. Mench, ECS Transactions, 58 (1), 1375-1382 (2013).

4. A. Z. Weber and J. Newman, Journal of the Electrochemical Society, 151 (2), A311-A325 (2004).

5. K. Knehr, E. Agar, C. Dennison, A. Kalidindi, and E. Kumbur, Journal of The Electrochemical Society, 159 (9), A1446-A1459 (2012).

6. R. Darling, K. Gallagher, W. Xie, L. Su, and F. Brushett, Journal of The Electrochemical Society, 163 (1), A5029-A5040 (2016).

7. Y. A. Gandomi, D. Aaron, T. Zawodzinski, and M. Mench, Journal of The Electrochemical Society, 163 (1), A5188-A5201 (2016).

8. Y. A. Gandomi, T. A. Zawodzinski, and M. M. Mench, ECS Transactions, 61 (13), 23-32 (2014).

9. C. Sun, J. Chen, H. Zhang, X. Han, and Q. Luo, Journal of Power Sources, 195 (3), 890-897 (2010).

10. Q. Luo, L. Li, Z. Nie, W. Wang, X. Wei, B. Li, B. Chen, and Z. Yang, Journal of Power Sources, 218 15-20 (2012).

Figure 1
Chemically Functionalized Graphene for High Performance Lithium/Sulfur Batteries
Authors: Zhang Yuegang
Published: February 2020

Carbon is an indispensible material for electrochemical energy storage applications. Graphene, with its high conductivity, high surface area, and high mechanical strength, has emerged as a magic material in the electrodes of the most advanced supercapacitors and lithium batteries. In this talk, I will demonstrate that graphene, with proper chemical functionalization, could play an important role in improving the lithium/sulfur cell’s active material utilization, specific capacity, as well as its cycle life. Using a nitrogen-functionalized graphene–sulfur electrode, we have achieved ultra-stable cycling exceeding 2000 cycles with a capacity decay rate as low as 0.028% per cycle. To understand the underlying mechanism of the electrochemical reaction processes, we developed various in-situ experimental tools so that we can conduct real time TEM and SEM Raman investigation during electrochemical measurements.  Based on these in-situ and other ex-situ characterization results, we develop a way to prevent lithium dendrite formation by using an optimized electrolyte and to minimize sulfur loss through the chemical interactions of the functional groups on graphene with the active electrode material, i.e. sulfur or lithium sulfide, as well as with the intermediate lithium polysulfide products.
Substrate-Integrated Nickel-Iron Ultra-Battery with Hematite Nano-Rods and Nickel Oxide Nano-Flakes As Respective Negative and Positive Plates
Authors: Sarkar Debasish , Shukla Ashok Kumar , D. Sarma D.
Published: February 2020

A substrate-integrated nickel–iron ultra-battery is realized using nickel oxide (NiO) nano-flakes and hematite (α-Fe2O3) nano-rods as electroactive materials for its positive and negative electrodes, respectively. Direct growth of electro-active materials on highly-conductive stainless steel substrate enhances mechanical stability of the system together with the reduction in its internal resistance. The proposed nano-architectural design of the electroactive materials provides large number of interaction sites for the electrolytic ions with the electrode materials in conjunction with short ion-diffusion paths, which significantly improve the capacitive performance of individual electrodes and hence of the fabricated ultra-battery. As a consequence, hematite nano-rod electrode exhibits a maximum specific capacity of ~ 45 mAh/g (191 F/g) at a current density of 1 A/g while NiO nano-flake electrodes are found to have specific capacity of ~ 51 mAh/g (366 F/g). The as assembled ultra-battery has the specific capacity value of ~ 36 mAh/g (94 F/g and volumetric capacitance ~ 0.77 F/cm3) at a current density of 0.5 A/g in a potential window between 0V and 1.4 V, with capacitance retention of ~ 60 % of its original value when the load current-density is increased 20 times. More importantly, maximum energy and power density values achieved with the ultra-battery are ~ 25 Wh/kg and ~7 kW/kg, respectively, which are superior to other recently reported pristine nickel, iron and other transition metal/metal oxide-based energy storage devices.
VO2 Nanoplatelets: A High Energy Electrode Material for Lithium Ion-Hybrid Electrochemical Capacitors
Authors: Satish Rohit , Vanchiappan Aravindan , Wong Chui Ling , Srinivasan Madhavi
Published: February 2020

Lithium ion hybrid capacitors (LIC) is an energy storage solution that combines the best of both worlds in terms of high power and high energy density. One of the participating electrodes stores charge by a faradaic mechanism (battery) while the other electrode stores charge by the formation of an electrical double layer (supercapacitor). This configuration allows for the exploitation of the niche gap between batteries and supercapacitors, allowing for the development of a possible energy storage solution for Plug in hybrid vehicles with fast charging and long range capabilities.

Vanadium dioxide has recently received much attention because of their high capacity when compared to other vanadium analogues. It consists of sheets of VO6 octahedras linked with each other at the corner, the layered structure allows for good lithium kinetics. The high capacity of Vanadium dioxide even at high power loads is postulated to mitigate one of the main issues faced by LIC’s, that the power density of the device is limited by the battery electrode and most battery electrodes tend to fail at high power loads.

Vanadium Dioxide nano-platelets were synthesized using a mechanically assisted hydrothermal reaction. The material was characterized using X-ray diffraction to check for phase purity, scanning electron microscopy and high resolution tunneling electron microscopy were used to characterize the effects of agitation on the morphology of the sample. The morphology is then co-related to the electrochemical performance of the material to develop an understanding about the effect of mechanical agitation on cell performance.

Comprehensive electrochemical studies were performed on both VO2 and commercial Activated carbon (acts as the supercapacitor electrode) to determine the mass loading in a full cell arrangement. Half cell studies on VO2 were conducted between 2-3 V vs. Li a high capacity of ~250 mAh g-1 was recorded with barely any capacity drop at high current rates. Because of the robustness of VO2 during high current operations it can be applied in applications that require to store a large amount of energy and at the same time be able to undergo fast charge discharge cycles.
Improved Performance for Lithium Excess Layered Oxides By Solid-State Surface Coatings
Authors: Carroll Kyler J. , Li Bin , Strand Dee
Published: February 2020

The design of high voltage and high capacity cathode materials for lithium ion batteries are important for the pressing demand of electric vehicles and portable devices. Of the cathode materials, the lithium excess nickel manganese cobalt layered oxides (Li-Rich NMC), where the lithium-to-transition metal ratio is greater than 1, have been looked at as an alternative due to the possibility of utilizing more than 1 Li in the chemical formula unit which would significantly increase the capacity. However, despite much effort from researchers, the extensive commercial application of the lithium excess material is hindered by several deficiencies, namely the low initial coulombic efficiency, poor cycle life, and poor rate performance. These deficiencies have mainly been attributed to the complicated structural evolution and the formation of a cathode solid electrolyte interface (SEI) layer at the higher voltages (>4.5V). As a result of these surface features, many researchers have investigated the role of surface modification on improving the electrochemical properties. An effective strategy has been through chemical treatments and post-annealing steps to induce the formation of a surface spinel structure prior to electrochemical cycling, which has shown to improve the first cycle coulombic efficiency and rate performance. However, the first cycle coulombic efficiency and the associated cycle stability of these surface treated samples still need further improvement. In this work, at Wildcat Discovery Technologies, we investigate several families of surface coatings, prepared by solid- state synthesis techniques, and show that by modifying the surface coating we can greatly enhance the first cycle coulombic efficiency while also maintaining, or in some cases improving, the cycle stability and rate performance of the Li-Rich NMC material. Wildcat has evaluated the performance of hundreds of surface coatings and show that certain families tend to improve all metrics. In addition we show that certain families reduce gas generation during the first cycle as well as subsequent cycles over the pristine the Li-Rich NMC material.
Investigating the Role of Transition Metal Deposition on Solid Electrolyte Interphase Formation and Growth Using Redox Shuttles
Authors: Jaini Rajiv , Fuller Thomas F
Published: February 2020

Transition metal based electrodes are attractive positive electrode materials for lithium ion-batteries due to their high energy densities and large capacities.  However, these positive electrode materials are prone to dissolution of the transition metal structure into the electrolyte.  The subsequent result of the dissolution is accelerated capacity and power fade.  Investigation into the dissolution phenomena shows that after dissolution, the transition metals transport to the negative electrode.  It is there where the metals ions deposit on the negative electrode surface, catalyzing solid electrolyte interphase (SEI) growth and blocking active sites for intercalation (1-3).  In spite of these studies, much remains unclear about variations in the morphology and electronic passivity of the SEI due to transition metal deposition on the negative electrode surface.

In this work, we investigate changes in the morphology and electronic passivity of the SEI using redox shuttles.  We introduce manganese, nickel, and cobalt-based transition metal salts over a range of concentrations to the primary electrolyte.  SEIs are formed on glassy-carbon electrodes by applying potentiostatic holds and cyclic voltammetry (CV).  After formation, the SEI is probed using the ferrocenium-ferrocene redox shuttle.  A mathematical model of the electrode-electrolyte interface is used to quantify the thickness and porosities of formed SEIs.

Figure 1(a) shows the effectiveness of the redox shuttle in characterizing the magnitude of passivation on the working electrode surface.  The working electrode is glassy carbon and primary electrolyte is (1:1 wt%) ethylene carbonate : diethyl carbonate with 1 M LiPF6 salt.  CVs were measured at ν = 10 mV s-1 around the equilibrium

redox potential, ~ 3.24 VLi/Li
+.  Increasing passivation time reduces redox peak currents, suggesting that surface passivation limits redox kinetics.  Figure 1(b) shows experimentally obtained and simulated CVs, demonstrating that the system can be effectively modeled with an SEI.

References

1.         T. Joshi, K. Eom, G. Yushin and T. F. Fuller, Journal of the Electrochemical Society, 161, A1915 (2014).

2.         C. Delacourt, A. Kwong, X. Liu, R. Qiao, W. L. Yang, P. Lu, S. J. Harris and V. Srinivasan, Journal of the Electrochemical Society, 160, A1099 (2013).

3.         J. Lu, C. Zhan, T. Wu, J. Wen, Y. Lei, A. J. Kropf, H. Wu, D. J. Miller, J. W. Elam, Y.-K. Sun, X. Qiu and K. Amine, Nat Commun, 5 (2014).

Figure 1
Transition Metal Sulfide Based Cathode Materials for Efficient Hybrid Supercapacitors
Authors: Chen Yin-Ying , Chou Shu-Wei , Lin Jeng-Yu
Published: February 2020

Supercapacitors (SCs) have been widely recognized in a wide range of energy storage applications over the past decade, such as hybrid electric vehicles, mobile electronic devices, large industrial equipments, memory backup systems, and military devices, due to their unique properties including higher specific power density (10 kW kg-1) than batteries, and higher specific energy density (5-10Wh kg-1) than conventional dielectric capacitors without sacrificing cycle life (>100,000 cycles). In recent years, nanostructured metal sulfides have been intensively investigated as SCs electroactive materials.

In this study, nickel and cobalt binary sulfide nanoparticles decorated on the surface of multi-walled carbon nanotubes (designated as Ni-CoS/MWCNT composite) and Ni3S2 thin films directly deposited onto Ni foam is successfully prepared by a facile glucose-assisted hydrothermal method and pulse-reversal (PR) deposition approach. On the basis of tuning the Ni/Co molar ratio of the Ni-CoS/MWCNT composites, the optimized Ni-CoS/MWCNT composite was employed as the cathode and a reduced graphene oxide was used as the anode to fabricate a hybrid supercapacitor (HSC). As-fabricated HCS is able to be operated reversibly in a full voltage region of 0–1.6 V and achieves a high specific capacity of 33 mAh g−1 at 1 A g−1. Moreover, it can still deliver a maximum energy density of 23 Wh kg−1 at a power density of 684 W kg−1. Furthermore, the HSC still retains 90% of its initial discharge capacity after 2000-cycle charge/discharge test at a fair high current density of 4 A g−1. Additionally, another HSC is then assembled by using the optimized PR-Ni3S2 electrode as cathode and carbon fiber cloth (CFC) as anode, respectively. The HSCs can be operated with a potential window between 0 and 1.8 V and deliver a high specific capacity value of 25.5 mAh g-1 at 0.5 A g-1. Moreover, the energy density and power density of the HCS can be achieved up to 28.8 Wh kg-1and 564 W kg-1, respectively. The most important thing is that the HSC displays excellent cycling stability with only 20% capacity loss after 5000 cycles. As a result, the highly efficient HSCs can be achieved based on the transition metal sulfide based materials as cathodes
Lithium-Ion Capacitor Based on Electrodes Constructed Via Electrochemical Spray Deposition
Authors: Agrawal Richa , Wang Chunlei
Published: February 2020

Conventional Electrochemical double-layer capacitors (EDLCs) are well suited as power devices that can provide large bursts of energy in short time periods. However, their relatively poor energy densities hinder their application in devices that require simultaneous supplies of both high energy and high power. In the wake of addressing this shortcoming of EDLCs, the concept of hybridization of lithium-ion batteries (LIBs) and EDLCs has started to gain popularity in recent years. Such a device, generally referred to as the “lithium-ion capacitor” typically utilizes a lithium intercalating electrode along with a fast charging capacitor electrode in a lithium-containing electrolyte.  Herein we have constructed a lithium ion capacitor comprising a Li4Ti5O12 (LTO) anode and a graphene and carbon nanotube (G-CNT) composite cathode using electrostatic spray deposition (ESD). The morphology and material properties were studied scanning electron microscopy and X-ray diffraction studies, respectively. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements were carried out to evaluate the electrochemical performance of both half cells and full cells. The details will be presented at the conference.
Performance Evaluation of Intermediate-Temperature Reversible Solid Oxide Fuel Cell at VPS
Authors: He Hongpeng , Wood Anthony , Joia Tahir , Krivy Mark , Steedman Dale
Published: February 2020

Hydrogen has been considered as a potential alternative fuel for future energy supplies and can be produced through high temperature steam electrolysis. The technology can be realized through reversible operation of solid oxide fuel cells (SOFCs), involving reduction of water at the cathode to form hydrogen and rejection of oxygen to air at the anode. Versa Power Systems (VPS) is a developer of SOFC technology focused on large stack and system development for commercial applications. In recent years VPS has been developing RSOFC material systems for the purpose of future commercial development of RSOFC stacks.  VPS has demonstrated significant technical improvements in RSOFC materials technology including demonstrated cell operation up to 6 A/cm2 with <1.67 V operating voltage at 800°C.  Recent work has focussed on the effects of testing conditions on cell durability using performance testing (polarisation) and electrochemical impedance spectroscopy.
Engineering Photovoltaic Waste Kerf-Loss Silicon into a Practically Applicable Anode for Lithium Ion Battery
Authors: Selvaraj Baskar , Huang Tzu-Yang , Wu Nae-Lih
Published: February 2020

Silicon has been extensively studied as a lithium ion battery anode due to its high capacity and abundant in nature. Huge volume expansion (>300%) and relatively low electrical conductivity of this material resulted in pulverization, unstable SEI formation and poor cycling stability. Preparation of silicon nanomaterials (nanoparticles, nanowires, nanotubes and porous silicon) combined with carbon (carbon nanotubes, graphene and carbon coating) has significant achievements in addressing these problems but lacking in satisfying the requirements of practical application cost, high mass loading to have high capacity per unit area and simple method for the mass production. Fast growing solar industry produces tons of valuable crystalline silicon containing kerf loss (Kf) waste during slicing of the silicon ingots. Utilization of this Kf as a silicon source will provide an environmental friendly cheap constant source for the lithium ion battery anode and complement each other in the aspect of power generation and storage.

 Kf silicon source with simple industrially mature high-energy ball milling (HEBM) is used here as a method for the material preparation. Instead of separating robust non-conductive abrasive SiC particles from Kf, it is adopted as millers to reduce Si particle size and skeleton to accommodate silicon volume expansion. In addition to SiC, nickel is added further to absorb volume expansion and to serve as electrical conductor along with the small amount of carbon black. Milling and calcination of Kf, nickel oxide and carbon black leads to the formation of micrometer sized agglomerates (~ 10 µm) composed of nanometer sized silicon, silicon carbide, nickel and carbon black (SSNC) ternary composite particles. This reduction of Si particle size with agglomerates formation gives rise to high particle tap-density and helped to achieve high mass loading on the electrode. This SSNC ternary composite has exhibited high reversible capacity > 800 mAh/g with comparably low first-cycle irreversibility.  Reduction of silicon and engineering of its surface with non-conductive SiC and conductive nickel and carbon composite successfully reduced the volume expansion, leading to substantially enhanced cycle stability.

Figure 1
Designing Sandwich Structured Cu/SnCu/Cu Film and Its Use As Negative Electrode for Lithium Ion Batteries
Authors: Bilici Burcin , Polat Deniz Billur , Keles Ozgul
Published: February 2020

We demonstrate the design and the fabrication of Cu/SnCu/Cu sandwich-like structured film by electrochemical deposition method. The Cu layer at the current collector/electrode interface increases the adhesion of the film. And the Cu layer at the electrode/electrolyte interface is believed to hold the electrode together to prevent the delamination and promotes a stable interface formation to optimize the electrochemical performance of the electrode. Moreover, Cu atoms in the SnCu layer of the Cu/SnCu/Cu sandwich-like film serve as conductive pathways to support an effictive lithiation/delithiation reactions between Sn and Li, plus act as buffer to tolerate the mechanical stress induced in the galvanostatic test. Herein it is important to note that possible intermetallics formation between Cu and Si might enhance the reversibility of the lithiation reaction of Sn with Li.

Therefore to promote the intermetallic formation in the film, a heat treatment (200˚C, 48h under vacuum atmosphere) has been applied. The galvanostatic test result shows that a remarkable improvement is noted when heat treated Cu/SnCu/Cu film is used as anode.
Understanding the Factors That Improve the Cycling Performance of Silicon Anode for Li-Ion Batteries
Authors: Alvarado Judith , Schroder Kjell W , Yersak Thomas A. , Stevenson Keith J. , Meng Ying Shirley
Published: February 2020

The high gravimetric capacity of lithiated silicon has motivated research as a potential anode for lithium ion batteries; however, major challenges remain for the implementation of silicon in commercial devices. During the lithiation process, a portion of the Li ions are consumed as the electrolyte is reduced to inactive side products from parasitic reactions, forming a solid electrolyte interphase (SEI). The SEI components should be electronically insulating and passivate the active material’s surface from further solvent reduction.1 However, due to the mechanical instability of silicon during lithiation, it prohibits the formation of a stable SEI causing capacity loss during cycling. In order to solve this issue, fluoroethylene carbonate (FEC) electrolyte additive has been widely used.2 However, the connection between SEI stability and FEC needs to be further investigated on a silicon model system.

Herein, SEI formed from LiPF6-carbonate based electrolytes, with and without FEC were investigated on 50nm amorphous silicon thin film electrodes. Figure 1 (a) demonstrates the excellent cycling performance of FEC over prolonged cycles compared to its counterpart. Anhydrous and anoxic X-ray photoelectron spectroscopy (Figure 2 (b)) and time-of-flight secondary ion mass spectrometry depth profiling techniques were used to accurately characterize the SEI structure and composition.  These results show that FEC reduction leads to fluoride ion and LiF formation, consistent with previous results.3 We believe that the effectiveness of FEC at improving the Coulombic efficiency and capacity retention is due to fluoride ion formation from reduction of the electrolyte, which leads to the formation of a kinetically stable SEI comprised of predominately inorganic compounds. This work is funded by the Office of Vehicle Technologies, U.S. Department of Energy under the Advanced Battery Materials Research (BMR) Program.

Reference:

[1] Verma, P.; Maire, P.; Novák, P. Electrochim. Acta 55 (2010) 6332–6341.

[2] Xu, C.; Lindgren, F.; Philippe, B.; Gorgoi, M.; Björefors, F.; Edstrom, K.; Gustafsson, T. Chem. Mater. 27 (2015) 2591-2599.

[3] Leung, K.; Rempe, S. B.; Foster, M. E.; Ma, Y.; Martinez del la Hoz, J. M.; Sai, N.; Balbuena, P. B. J. Electrochem. Soc. 161 (2013) A213–A221.

Figure 1
Visualizing the Solid Electrolyte Interphase Layer Evolution in Silicon Electrode
Authors: Sina Mahsa , Alvarado Judith , Shobukawa Hitoshi , Meng Ying Shirley
Published: February 2020

Silicon is a promising anode candidate in Li-ion batteries with a theoretical capacity more than ten times that of the commercial graphite anodes (372 mAh/g). However, Si electrodes suffer from rapid capacity fade during electrochemical cycling. One of the more successful strategies for dealing with the capacity loss and continuous solid electrolyte interphase (SEI) formation on Si electrodes has been the use of battery electrolyte additives such as fluoroethylene carbonate (FEC) [1-4]. In this work we used a combination of Annular Dark Field - Scanning Transmission Electron Microscope (ADF-STEM) imaging and Electron Energy Loss Spectroscopy (EELS) techniques in order to understand the effect of FEC on the chemical and morphology evolution of Silicon and SEI layer during cycling. We observed that upon lithiation crystalline Si converted into the amorphous LixSi alloy and two layers formed on the outermost surface of the electrode including: 1- SEI and 2- LixSiOy. It was found that the presence of FEC suppresses the formation of LixSiOy layer and leads to the formation of uniform SEI layer around the LixSi particles with high LiF content. Such STEM/EELS study correlates the morphology and chemistry of the Silicon and SEI layer for the first time and provides valuable insights into the electrochemicalperformance of Si electrodes.

Acknowledgements

This research is funded by the Office of Vehicle Technologies, U.S. Department of Energy under the Advanced Battery materials Research (BMR) Program.

References

[1] Philippe B., G. G. (2013), Chemistry of Materials, 25: 394-404.

[2] Xu C., F., et. al. (2015),  Chemistry of Materials, 27:2591-2599..

[3McDowell M. T., et al. (2012), Advanced Materials 24: 6034-6041.

[4] Sina M., et al. (2015), Journal of Phys. Chem. C, 119: 9762–9775.
(Invited) The Effect of Increased Dielectric Screening on Bimolecular Recombination of Photogenerated Charges in Polymer:Fullerene Bulk Heterojunctions
Authors: Mozer Attila Janos , Clarke Tracey M , Zhang Guanran
Published: February 2020

Bimolecular recombination studies reveal a one order magnitude slower bimolecular recombination when normalized to charge mobility in a polymer:fullerene bulk heterojunction solar cell with a dielectric constant of seven. The techniques used were charge extraction using nanosecond switch combined with charge extraction by linearly increasing voltage and integral mode time of flight measurements. The measured high dielectric constant in the polymer:fullerene blend is due to the exceptionally high dielectric constant (16.7) of the conjugated polymer donor component employed. This value, indicative of increased dielectric screening of charges compared to most organic solar cell materials with a typical dielectric constant around 4,is one of the highest reported to date. The slower bimolecular recombination mentioned above is compared to well established poly(3-hexylthiophene) and low badngap polymer PCPDTBT:fullerene heterojunctions, and is explained by the smaller coulomb capture radius in a diffusion controlled recombination model. Longer charge carrier lifetimes together with a larger charge mobility in the high dielectric constant bulk heterojunctions leads to larger fill factors (0.6) and excellent photovoltaic performance in solar cells using large active layer thicknesses approaching 300 nm. Ultimately, increasing the dielectic constant of organic photoactive laterials to and beyond 10 is expected to bridge the performance gap between inorganic and organic solar cells.
(Invited) Selective Synthesis of Photoelectrochemical Active Co8S15 Cluster inside the Bowl-Shaped Templating Pentaorgano[60]Fullerene Ligand
Authors: Matsuo Yutaka
Published: February 2020

Metal chalcogenide clusters are structural motifs utilized, for example, in enzymatic active sites, catalysts, and optical/optoelectronic materials. Among non-biomimetic cluster complexes, those consisting of cobalt and sulfur are particularly attractive due to their potential as catalysts, electrocatalysts, semiconducting materials, and so forth. Moreover, intriguing properties have been reported for cobalt sulfide nanoparticles, giving rise to interest in cobalt–sulfur cluster complexes. However, synthetic routes to cobalt–sulfur cluster complexes are quite limited and their structural diversity is very low. Thus, development of facile cobalt–sulfur sources and terminal ligands is strongly desired. In this presentation, we discuss the selective synthesis of the well-defined Co8S15 cluster complex starting from a cobalt trisulfide complex. The precursor cobalt trisulfide complex served as a cobalt–sulfur source as well as a powerful sterically templating terminal ligand. A corner-sharing double-cubane-like cobalt–sulfur cluster was selectively synthesized from an easily prepared cobalt trisulfide complex of pentaaryl[60]fullerene. The obtained cluster contained two Co4S5 cubane-like units coordinated by thiolate and disulfide ligands. The bowl-shaped steric template as well as the metastable cobalt trisulfide moiety played important roles in the exclusive cluster formation. Crystallographic, electrochemical, and magnetic measurements elucidated a mixed-valence nature of the cluster with two high-spin cobalt(II) centers. The present study will provide new opportunities for development of artificial functional metal–sulfur cluster complexes for various applications.

Figure 1
(Invited) Polyarylations of Heterofullerenes
Authors: Hirsch Andreas
Published: February 2020

We will report on a variety of new arylation reactions leading to well defined oligoadducts of the heteofullerene C59N. These adducts contain an integral pyroll subunit. On the way the full arylation a variety of mono- and bishydrides could be isolated as well. All new compounds were fully characterized including x-ray crystallography. Based on the experimental data a convinving reaction mechanism describing the formation of these new fullerene adducts was proposed.
(Invited) C70 As a Photocatalyst for Oxidation of Benzylamines to Imines
Authors: Kumar Rakesh , Yamakoshi Yoko
Published: February 2020

Photosensitivity is one of the most important physico-chemical properties of fullerenes. Photoexcited C60 and C70 can cause the electron transfer (type I)1 or energy transfer (type II)2,3 reaction under visible light irradiation in quite high quantum yields (quantitative). These reactions have been used to develop new functional materials for the application of photovoltaic devices and photodynamic therapy agents. Especially in the latter application, generation of reactive oxygen species (ROSs)4 such as 1O2 and O2•–
5,6is used to affect the biological molecules.

The generation of 1O2 has been also used in the organic reaction. Using fullerenes as photocatalyst, oxidation of olefins,7 phenols8 and sulfides9 were reported. In this study, we used C70 for the oxidation of benzylamines. Compared to C60 and other commonly used photosensitizers such as tetraphenylporphyrin (TPP),10,11 C70 could catalyze the oxidation of benzylamines to corresponding imines efficiently with lower catalyst loading (0.01 mol %). The reaction worked also under the lower energy of lights using blue (max 470 nm) and green (max 520 nm) diodes. Reaction processed in clean manner without any significant amount of side product, and removal of the C70catalyst was carried out easily by just simple precipitation and filtration.

(1) Arbogast, J. W.; Foote, C. S.; Kao, M. J. Am. Chem. Soc.
1992, 114, 2277. (2) Arbogast, J. W.; Darmanyan, A. P.; Foote, C. S.; Rubin, Y.; Diederich, F. N.; Alvarez, M. M.; Anz, S. J.; Whetten, R. L. J. Phys. Chem.
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(Invited) Exohedral Functionalization of Fullerenes: New Insights from Computational Studies
Authors: Rodríguez-Fortea Antonio , Abella Laura , Moreno Antonio , Poblet Josep M.
Published: February 2020

Computational studies have helped to understand the experimental distribution of regioisomers for a wide range of reactions on empty and endohedral fullerenes, as well as to elucidate their reaction mechanisms. In this communication, we will present the latest results in our group regarding chlorination, fluorination and hydrogenation reactions on empty and endohedral fullerenes of different sizes (C50 to C84). Moreover, the distribution of bisadducts for some cycloaddition reaction on H2@C60 will be also analyzed.
(Invited) Chemically Modified Two-Dimensional Nanoelectronic Heterostructures
Authors: Hersam Mark C.
Published: February 2020

The outstanding properties of graphene have been established on pristine samples in idealized conditions. However, for most applications, graphene needs to be chemically functionalized in a manner that either preserves its intrinsic properties or modifies its properties in a manner that enhances functionality. Towards these ends, several noncovalent chemistries have been demonstrated and characterized at the molecular scale with ultra-high vacuum scanning tunneling microscopy including 3,4,9,10-perylenetetracarboxylic dianhydride and 10,12 pentacosadiynoic acid.  These self-assembled monolayers are shown to be effective atomic layer deposition seeding layers for dielectrics (e.g., Al2O3, HfO2, and ZnO), which allows for substantial improvements in the uniformity and reliability of metal-oxide-graphene electronic devices. On the other hand, covalent modification schemes based on free radical chemistries allow for more fundamental changes to the electronic and chemical properties of graphene. In particular, atomic oxygen has been established as an effective method for homogeneously and reversibly functionalizing graphene with epoxide groups. In addition to chemically doping graphene, epoxidation yields local modification of the graphene bandstructure and provides pathways for further chemical functionalization, thereby expanding the suite of chemically modified graphene heterostructures. Finally, this talk will conclude with ongoing work in our laboratory to extend the chemical modification strategies for graphene to other two-dimensional materials including ultrathin silicon [1,2], black phosphorus [3,4], and transition metal dichalcogenides [5].

[1] A. J. Mannix, B. Kiraly, B. L. Fisher, M. C. Hersam, and N. P. Guisinger, “Silicon growth at the two-dimensional limit on Ag(111),” ACS Nano, 8, 7538 (2014).

[2] B. Kiraly, A. J. Mannix, M. C. Hersam, and N. P. Guisinger, “Graphene-silicon heterostructures at the two-dimensional limit,” Chem. Mater., 27, 6085 (2015).

[3] J. D. Wood, S. A. Wells, D. Jariwala, K.-S. Chen, E. Cho, V. K. Sangwan, X. Liu, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Effective passivation of exfoliated black phosphorus transistors against ambient degradation,” Nano Lett., 14, 6964 (2014).

[4] X. Liu, J. D. Wood, K.-S. Chen, E. Cho, and M. C. Hersam, “In situ thermal decomposition of exfoliated two-dimensional black phosphorus,” J. Phys. Chem. Lett., 6, 773 (2015).

[5] X. Liu, I. Balla, H. Bergeron, G. P. Campbell, M. J. Bedzyk, and M. C. Hersam, “Rotationally commensurate growth of MoS2 on epitaxial graphene,” ACS Nano, DOI: 10.1021/acsnano.5b06398 (2015).
Photoelectronic Effects with Graphene Channels Interfaced with Quantum Dots Arrays
Authors: Miao Xin , Trivedi Samarth , Grebel Haim
Published: February 2020

The electrical and photo-electronic properties of graphene-based field effect transistors (GFETs) were studied when the single layer graphene served as the transistor channel, while interfaced with well organized, isolated semiconductor quantum dots (QD) array. The photoluminescence (PL) of the QDs as a function of the drain-source (Vds) and the gate-source (Vgs) bias was studied.

Graphene, a two-dimensional, single layer thick crystalline form of carbon atoms, has outstanding physical properties, such as high conductivity, chemical inertness, mechanical robustness and unusual dispersion relations [1]. In the past, we studied graphene layer(s) when suspended over nano-pore structures [2-6]. Here we used anodized aluminum oxide (AAO) as the perforated substrate, and core/shell CdSe/ZnS semiconductor quantum dots (QD) as the photo-sensitive material. The QD were imbedded in the AAO pores.

The GFETs were fabricated by transferring a single layer of graphene on top of the QD imbedded AAO. The array of holes on the AAO substrate were 25-30 nm in diameter and with a pitch of 100 nm. For the photoluminescence (PL) measurements, a 10 mW Ar ion laser at 488 nm was used in confocal arrangement. Coupling of the incident and/or emitted light with the surface Plasmon/Polariton (SPP) mode was observed as a peak in PL curve as a function of the sample's tilt angle with respect to the incident optical beam. The fluorescence peak of the QDs decreased monotonously as a function of Vgs and Vds alluding to the control of PL by the biasing potentials. The effect of white-light intensity on the sample conductivity was studied, as well: the difference in Ids between illuminated and non-illuminated cases was substantially affected by the biasing potentials.

[1]           K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva and A.A. Firsov, “ Electric Field Effect in Atomically Thin Carbon Films”,  Science, 306, 666 (2004).

[2]           A. Banerjee, R. Li and H. Grebel, “Surface Enhanced Raman with Graphenated Anodized Aluminum Oxide Substrates: the Effect of Sub-Wavelength Patterns”, Nanotechnology, 20 (29), art. no. 295502 (2009).

[3]           A. Banerjee and H. Grebel, “Depositing Graphene Films on Solid and Perforated Substrates”, Nanotechnology, 19 1-5 art. no. 365303 (2008).

[4]           Ruiqiong Li, and Grebel Haim, “Surface Enhanced Fluorescence”, IEEE Sensors, 10(3), 465-468 (2010) doi: 10.1109/JSEN.2009.2038513.

[5]           R. Li, A. Banerjee and H. Grebel, “The possibility for surface plasmon lasers”, Optics Express, 17, 1622-1627 (2009).

[6]           A. Banerjee, R. Li and H. Grebel, "Surface plasmon lasers with quantum dots as gain media", Appl. Phys. Letts., 95, 251106 (2009); doi:10.1063/1.3276273.
Band Gap Tuning of Germanene Nanoribbon Using Chemical Functionalization
Authors: Monshi Md Monirojjaman , Mehdi Aghaei Sadegh , Calizo Irene
Published: February 2020

Graphene as a 2D carbon nanostructure has drawn tremendous interest worldwide because of its extremely high mobility and unique electronic, magnetic, and surface properties but opening a band gap remains challenging. Other 2D materials have emerged as promising materials that may be more easily altered to have a band gap, high mobility, and on/off ratio. Germanene with its buckled two-dimensional structure exhibits extremely high mobility, massless fermions behavior, and strong spin-orbit coupling which has drawn tremendous interest for high performance devices. However, it has no intrinsic band gap and low structural stability which are needed for logic and switching devices. Despite numerous attractive features in germanene it, like graphene, exhibits a semi-metallic zero band gap. Applying electric field, chemisorption of adatom species, introducing periodic nanoholes, doping and edge functionalization are all techniques aimed at opening a bandgap in germanene. Here we present a density functional theory based study of the influence of edge-functionalization using hydrogen (-H and -2H) and halogen (- F, -Cl, -Br, -I, -2F,-2Cl, -2Br, -2I), -S atoms and –SH, -OH, -CH3 groups termination. An overview is given of the influence of these edge-functional groups attached to different germanene nanoribbon (GNR) structures of varying width ranging from 6 to 19, focusing primarily on band gap. Additionally, the dependence of armchair GNR band gap on functionalization and ribbon width is explored. We found that edge functionalized armchair germanene nanoribbon (AGeNR) opened a band gap as small as 0.012 eV when functionalized by -2H and could be as high as 0.84 eV when functionalized with -2I. Nanoribbons could be classified into three families according to width as follows, W = 3K, 3K+1, and 3K+2. For mono-hydrogenated, fluorinated, chlorinated, hydroxyl termination, the band gap varied as EG (3K+2) < EG (3K) < EG (3K+1).  For di-hydrogenated, fluorinated, and chlorinated we found band gap follwed the periodicity EG (3K+ 1) < EG (3K +2) < EG (3K ). Formation energy studies revealed that the AGeNR produced a more stable structure with fluorine functionalization and -SH, -OH, -CH3 group’s termination also provides similar result with sizable band gaps. Simulation results suggest that the electronic structure of germanene is similar to graphene and silicene. Energy band gap tuning of AGeNR using edge functionalization may provide a new means of integrating germanene in optoelectronics, low power and high performance switching devices.
Kolbe Electrochemistry in Reversible Wavefunction Engineering of Epitaxial Graphene
Authors: Sarkar Santanu
Published: February 2020

Electrochemical methods to functionalize graphene have emerged as attractive protocols to covalently modify graphene in engineering a band gap and in altering its magnetic and solubility properties. Kolbe reaction, which involves the electrochemical oxidation of arylacetates (generation of α-naphthylmethyl radicals, in our present case), allows reversible grafting of radicals to graphene surface; the electro-erasing of the functional groups leads to graphene at its nearly pristine state. The surface coverage can be controlled from densely-packed (ideal as organic dielectrics) to sparsely functionalized surface (ideal for introducing reasonable band gap in graphene) with well-ordered structural patterning of the functional groups on graphene surface by fine adjustment of electrochemical conditions. Such a control of the layer structure and packing of the functional groups over the graphene surface is essential in the development of graphene applications.
Low Cost Fabrication of Graphene Oxide Films As Efficient Counter Electrode for Dye-Sensitized Solar Cells (DSSC)
Authors: Devarepally Kishore Kumar
Published: February 2020

Graphene-oxide was prepared by screen printing to validate as an alternative counter electrode material to platinum in dye sensitized solar cells. The synthesis of graphene oxide was carried out by modified Hummer’s method using graphite flakes.  Subsequently, graphene oxide paste was prepared by mixing α-terpineol and ethyl cellulose, which was screen-printed on FTO glass (TEC8) substrates. The screen printed films were subjected to annealing at 450°C for 30 minutes. The graphene oxide films were characterised by X-Ray Diffraction, Scanning Electron Microscopy and Raman spectroscopy for the required identification. The device fabrication was carried out by coupling TiO2 films soaked in N719 dye with Surlyn as the spacer between the electrodes.

The J-V measurements were carried out with the help of the solar Simulator AM1.5G condition under standard one Sun illumination. The DSSC fabricated with graphene oxide as counter electrode exhibited photoconversion efficiency of 5.58% whereas, platinum based devices showed photoconversion efficiency of 7.57%. The catalytic properties of graphene oxide films are being investigated by cyclic voltammetry and electrochemical Impedance spectroscopy. The present study suggests that graphene oxide counter electrodes can be considered as a promising alternative to platinum, with further optimisation, which clearly has advantages in terms of its abundance and low cost processing towards industrial prospects.