bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Reaction Mechanism of High-Entropy Oxides in Li-Ion Batteries
Authors: Jovino Marques Otavio , Timofeeva Elena V. , Segre Carlo
Published: July 2021

Recently, high-entropy oxides (HEOs) have emerged as an alternative conversion electrode material for next-generation Li-ion batteries (LIBs). The concept of entropy stabilization of numerous transition metal oxides (TMOs) in a single disordered solid solution phase opens new boundaries of materials design, providing the possibility of overcoming individual TMOs limitations by tailorable properties. Although conversion anode TMOs deliver high capacity due to multi-electron redox processes, they still suffer from large volume variation and severe structural changes, leading to electrode pulverization and resulting in drastic capacity fading. The individual contribution of each transition metal (TM) in the HEO structure to the electrochemical reaction mechanism and its structural stability is not yet well understood and prevents the rational design of HEOs with different electrochemically active sites that can be used to improve the Li-storage performance and battery cyclability. In this work, (MgCoNiCuZn)O nanoparticle anode materials were synthesized by solid state reaction and subsequent high energy ball milling. The system consists of five component bivalent ions sharing the same transition metal (TM) site in a rock-salt structure. Extended x-ray absorption fine structure (EXAFS) was used to investigate the change in the local structure around each TM in the pristine and galvanostatically cycled electrodes. The 1st, 2nd and 100th cycles in lithiated and delithiated states were studied, showing an initial capacity of ~550 mAh/g at a current density of 50 mA/g for the first couple of cycles, and ~650 mAh/g at 100 mA/g after 100 cycles. Our preliminary data reveal significant changes from the initially octahedral coordination of each TM, giving us insights about the electrochemical and structural role of each component. In the lithiated state, Co, Cu and Ni are reduced to a metallic state while Zn remains oxidized. Subsequent delithiation shows that Co and Ni are re-oxidized to some degree while Cu and Zn remain unchanged. In this presentation we will discuss the structural analysis of the local environment of each TM with a focus on their individual roles in the electrochemical performance of the HEO anode.
(Invited) Electrode Binder As an Enabling Material for Si Based Electrode
Authors: Liu Gao
Published: July 2021

Silicon (Si) is an attractive candidate for lithium-ion batteries because it delivers 10 times greater theoretical (∼4200 mAh/g) specific capacity than that of a traditional graphite anode (∼370 mAh/g). However, the widespread application of silicon materials has remained a significant challenge because of the large volume changes during lithium insertion and extraction processes disrupt both the Si electrode surface and electrode mechanical integrity. This large volume change causes electrode failure, leading to loss of the electrical contact and drastic capacity fading. Functional electrode binders can play multiple functions for Si electrode, including improved adhesion, lithium ion compensation, better ion and electric conductivity as well as surface and interface modification. Organic and polymer chemistry have provided almost infinity possibilities to modify the polymeric binders to include the desired functionalities. This presentation will discuss the specific molecular design principles and synthetic steps to realize the structures and functionalities of the binders, how these binders interact with different Si materials, and the electrochemical performances of the electrodes based on these binders.
High Adhesive Polyimide Binder for Silicon Anodes of Lithium Ion Batteries
Authors: Zhang Sanpei , Trask Stephen E. , Dunlop Alison , Polzin Bryant , Qin Yan , Jansen Andrew N. , Lu Wenquan
Published: July 2021

Silicon has been extensively studied as an anode material in lithium-ion batteries due to its extremely high theoretical specific capacity of 3578 mAh/g (assuming Li15Si4 as intermediate product). However, silicon undergoes huge volume variations during repeated discharge and charge, leading to poor electrode mechanical integrity, continual electrolyte decomposition and fast capacity decay. Developing high strength binders in silicon anodes have been considered as an efficient pathway to alleviate various capacity decay pathways.

Currently, lithiated poly acrylic acid (LiPAA) is mostly used as the binder for silicon electrodes due to its strong binding capability and (electro)chemical compatibility with Si and electrolyte. However, cracks at the electrode level can still be observed for the cycled electrodes, which suggests that a stronger binder is required to mitigate volume expansion of Si electrode and hold the particles together. Herein we study the polyimide (PI) materials as the binders for Si anode in an attempt to achieve stable cycling performance. With PI binder, the silicon electrode exhibits a higher tensile strength than that of conventional PAA binder. The strong adhesion of the PI binder suppresses the structural collapse of the Si negative electrode during lithiation/delithiation, enabling high capacity retention and stable cycle life. However, the PI crosslinking process requires high temperature and inert atmosphere, which is a challenge for its practical application. In this work, we explore various PI crosslinking conditions and their effects on electrochemical performance. This work offers us an alternative binder material with high tensile strength for the Si electrode.

Acknowledgement

We gratefully acknowledge the support from the U.S. Department of Energy's Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is operated for DOE office of Science by UChicago Argonne, LLC, under contract number DE-AC02-06CH11357.
Elucidation of Active Oxygen Sites upon Delithiation of Li3IrO4
Authors: Li Haifeng , Perez Arnaud , Taudul Beata , Boyko Teak , Freeland John , Doublet Marie-Liesse , Tarascon Jean-Marie , Cabana Jordi
Published: July 2021

Transformational increases in the storage capacity of battery cathodes could be achieved by tapping into the redox activity at oxide ligands in addition to conventional transition metal couples. Yet the key signatures that govern such lattice oxygen redox (LOR) have not been ascertained. Li3IrO4 has the largest reversible LOR, rendering it a unique model system. Here, X-ray spectroscopy and computational simulations reveal that LOR in Li3IrO4 is selectively compensated via O sites with 3 lone pairs, which are activated by Li/Ir disorder. The 2-electron LOR can be reversed to regenerate the initial state without unlocking competing bulk reactions observed in many other compounds. We uncover an intricate interplay between stoichiometry, O coordination and non-bonding states in LOR and pinpoint spectroscopic signatures. This interplay is indispensable to design materials with 3d metals that fulfill the promise of LOR to overcome the bottlenecks of current cathodes for future implementation in practical batteries.
Polymeric Species in Solid Electrolyte Interphase Identified with MALDI-TOF-MS Assisted By on-Electrode Chromatography
Authors: Fang Chen , Liu Gao
Published: July 2021

The solid electrolyte interphase (SEI) is a passivating layer on the electrode surface produced by decomposition of the electrolyte, which has key impact on the battery’s long-term cycling performance. The inorganic species in SEIs have been extensively investigated but the organic SEI components, especially the polymeric molecules, often remain a mystery partially due to the difficulties in identifying these organics of small to trace quantities in a complicated chemical environment. Here, we propose matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for detection of organic and polymer species in SEIs. MALDI is suitable for characterization of organic and polymer molecules at trace amount but is inconvenient to couple with chromatography methods for separation of the analytes. Therefore, on-electrode chromatography is introduced for fractionating different species on electrode surfaces, where the electrode itself serves as the stationary phase to realize separation upon solvent elution. This strategy has proved indispensable for effective MALDI characterization of organic species in SEIs. High-mass polyethylene oxide (PEO) and polymethacrylate molecules have been identified as electrolyte and additive decomposition products. The combination of MALDI-TOF-MS and on-electrode chromatography methods presents a promising strategy for identification of the organic and polymeric species in SEIs.
Correlation between Manganese Dissolution and Dynamic Phase Stability in Spinel-Based Lithium-Ion Battery
Authors: Liu Tongchao , Amine Khalil
Published: July 2021

Historically long accepted to be the singular root cause of capacity fade, transition metal dissolution and its subsequent anode deposition have been reported to interfere with Li intercalation and destroy the anode solid electrolyte interphase. However, as a vital battery component, cathode behavior under transition metal dissolution still remains unclear. Here we report an unequivocal relationship between capacity fade and both dynamic phase stability and surface chemical stability of the cathode. With spinel LiMn2O4 as a model system and a Li-rich LiMn2O4 control sample, clear evidence gathered through in-situ/ex-situ high energy X-ray diffraction and scanning transmission electron microscopy reveal, for the first time, that a combination of dynamic structural transformation and surficial transition metal dissolution are the dominant factors of cathode capacity fade. LiMn2O4 exhibits irreversible phase transitions driven by Mn(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks formed during repeated charge/discharge result in severe Mn dissolution. Meanwhile, fast Mn dissolution in turn triggers irreversible structural evolution. These two processes form a detrimental chemical-cycle that constantly consumes the capacity of spinel. Furthermore, we are able to reproduce the atomic structural advantages of Li-rich LiMn2O4 with Li/Mn disorder and surface reconstruction, effectively suppressing the irreversible phase transition and Mn dissolution. These findings, predominately caused by transition metal dissolution and a newly discovered irreversible phase transition, close the loop of understanding capacity fade mechanisms in spinel-based cells. This insight helps elucidate structure stability improvements found from Li enrichment and cation doped cathodes, allowing for development of longer life batteries.
The Mechanism of Li Plating on Graphite Particles
Authors: Gao Tao , Fraggedakis Dimitrios , Das Supratim , Chueh William C. , Li Ju , Bazant Martin
Published: July 2021

Lithium ion battery is the mainstream technology that is powering most of mobile applications (consumer electronics, power tools etc.) and in the future, our transportation by electrifying the vehicles. Current lithium ion battery can only support 1C charging (~50 mins for 80% charge), which is much longer than refilling gasoline car ( < 5 min). Extreme fast charging ( <10 min for 80%) is a very attractive technology that can address this problem. However, Li plating happens in graphite at high charge currents or low temperature, which causes battery performance degradation or even safety hazard (short-circuit, thermal runaway and even fire).

The core of addressing Li plating problem lies in understanding its mechanism. Despite Li ion battery has been invented for 30 years, a systematic understanding on the onset and growth of Li in graphite anode is still lacking. In this work, we elucidate the mechanism of Li plating, by investigating the interplay between Li intercalation and Li plating on a single graphite particle using in-situ optical microscopy coupled with electrochemical test. The results show Li plating happens when the surface of graphite saturates which shuts down the intercalation reaction. The saturation can happen much earlier than full lithiation of graphite particle due to solid diffusion limitation, resulting in severe under-utilization. The discovery sheds light on directions and guidelines of materials innovation or electrode design for achieving extreme fast charging.
Greener Rechargeable Lithium-Ion Batteries Using Plasma Processes at Atmospheric Pressure
Authors: Profili Jacopo , Rousselot Steeve , Tomassi Erica , Briqueleur Elsa , Beauchemin Maxime , Aymé-Perrot David , Stafford Luc , Dolle Mickael
Published: July 2021

Numerous efforts have been made to develop new thin films by using atmospheric pressure plasma process. Complex materials such as nanocomposite thin films [1.2], biodegradable coatings [3] and advanced chemical treatments on complex surfaces [4] have for example been studied.

Recently, we reported the use of an atmospheric pressure dielectric barrier discharge (DBD) to strongly modify the interfacial properties in lithium-ion batteries [5]. This work focuses on the chemical functionalization of composite electrodes used for aqueous electrolyte rechargeable batteries (ARLB). In this presentation, the physicochemical properties of the coating and electrochemical performance of such electrodes are investigated.

Plasma-deposited coatings were then characterized by SEM-EDX, FTIR and XPS. The electrical analysis indicates that the discharge remains stable during the process. This suggests that the substrate slightly affect the physical regime of the gaseous discharge. The SEM analysis of the plasma-treated electrode suggests a homogeneous surface treatment over a wide area. From the FTIR analysis, different chemical groups were highlighted.

Finally, the electrochemical performance of such electrodes was also investigated in a battery operation. Preliminary explanation of the fundamental mechanisms allowing the operation of the battery and ions diffusion through the plasma layer is attempted.

[1] J. Profili et al., Plasma Processes and Polymers, volume13, issue10, October 2016, 981-989

[2] P. Brunet et al., Plasma Processes and Polymers, volume 14, issue12, December 2017, 1700049

[3] M. Laurent et al., Plasma Processes and Polymers, volume 13, issue7, July 2016, 711-721

[4] S. Asadollahi et al., Materials 2019, 12(2), 219

[5] J. Profili et al., ACS Sustainable Chemistry & Engineering 8 (12), 4728-4733
A Framework to Optimize Electrode Morphology
Authors: Deng Changyu , Lu Wei
Published: July 2021

Since the invention of lithium-ion batteries, porous electrodes have been manufactured in essentially the same way: granulating active materials into powder, mixing them with some additives such as carbon black and binder, and pasting them on conductive substrate. Optimizations have been focusing on tuning parameters such as particle sizes, porosity and electrode thickness, with the assumption of a uniform electrode. Some recent work demonstrated better cell performance by engineering the shape of the electrode with features such as nano cylinders, tunnels and fractal branches. 3D printing has been used to fabricate the structure of batter electrode. On the simulation side, however, there have been few reports on freeform electrode shape optimization. Most shape optimizations assume a particular electrode pattern with a few adjustable dimensional parameters. Here we report a method to optimize porosity distribution of electrode without a prior assumption of the pattern. An NMC 333 electrode with lithium metal as the counter electrode is considered as an example. To find the optimal solid material distribution for maximum specific energy, we represented the NMC material distribution by discrete nodal design variables. To solve this high dimensional optimization problem, we used a gradient-free optimization algorithm, self-directed online learning optimization. We show that the method can produce an electrode pattern with the specific energy more than 15% higher than that of the uniform electrode. This generic distribution optimization approach provides a powerful tool for the design and optimization of porous electrodes.

Figure 1
First-Print-Right: Learning the Geometry Deviation of Additively Manufactured Metal Parts
Authors: Shan Yujie , Wang Xiaoqing , Mao Huachao
Published: July 2021

Geometry deviation is commonplace in metal-based additive manufacturing (AM), and the ability to predict geometry deviation is foundational to quality control. This paper presents computational learning strategies to compensate for the geometry deviation and ensure the part accuracy of additively manufactured parts. The learned computational model can predict the geometry deviation for the additively manufactured parts, optimize the process parameter (such as laser power and scan strategies) to mitigate the geometry deviation, and provide an edited 3D model that compensates for the geometry deviation. The measured points cloud data will be fully utilized to continuously improve the learning framework along with the simulation data, which will accelerate the widespread adoption of U.S. metrology equipment. The learning platform will generate test-artifacts to benchmark the simulations. This work will significantly reduce the need for extensive empirical testing to accurate part and shorten the design-to-product cycle time in metal AM.
(Invited) How Analysis Helps Guide Battery Recycling R&D at the ReCell Center
Authors: Gaines Linda , Dai Qiang
Published: July 2021

The ReCell Center was established by the US Department of Energy’s Vehicle Technologies Office to develop a practical process for recycling of lithium-ion batteries. But if a recycling process is actually going to be adopted by industry, it must be economical. And since a main motivation for electric vehicles is environmental, the process must be “green” as well. Therefore, early in their development, ReCell processes are subjected to careful technical and economic analysis, using our publicly available and award-winning EverBatt model, to verify that they will be economical and environmentally friendly. This presentation will describe processes under development and illustrate the use of technical and economic analysis to evaluate them and compare them to alternatives.
(Invited) Scaling, Coarse Graining, and Bottlenecks on the Microstructural Modeling of Lithium-Ion Batteries
Authors: García Edwin
Published: July 2021

Historically, the properties of materials for rechargeable lithium-ion batteries, solid oxide fuel cells, and other energy-related applications has been investigated by self-consistently averaging the effect of an individual representative material feature and incorporating it into coarse grained (one-dimensional) descriptions that capture the time-dependent electronic and ionic transport. Such an approach is based on using analytic solutions of simplified representations of grains, pores, or inclusions, and averaging them into models that aim to understand or engineer the macroscopic properties of the device or component at hand. However, if effects due to phase transformation kinetics, or the impact of defects such as vacancies or interstitials, dislocations, or grain boundaries are to be engineered, currently used averaging approaches will not capture the underlying multiphysical and microstructural richness of behavior of the device. In general, the modern development of advanced technology for energy applications demands: 1) the formulation of a methodology that provides an accurate description of the materials that integrate these devices at each length scale; 2) the systematic and mindful coarse-graining of lower length scale methodologies into higher length scale descriptions, and 3) the establishment of meaningful databases that enable the development of insight to understand and then engineer advanced, reliable, next generation devices. Here, by defining a thermodynamically consistent representation of materials that spatially resolves the multiphysical fields that results from formally considering microstructural features such as grain size, crystallographic texture, grain boundaries, particle size, and porosity, the time-dependent galvanostatic behavior is analyzed in lithium-ion batteries. Progress towards integrating the physical contributions of each individual phase and its processing-induced spatial distribution into advanced homogenized models is presented. The effect on the performance and degradations is analyzed. Reaches and limitations of well-known and emerging theories will be reviewed and compared, and efforts to accelerate to the limit of real time performance and degradation computations will be presented in an effort to explore the space of what is physically possible.
(Invited) Microkinetic Models for Plasma-Catalytic NH3 Synthesis: Effects of Catalyst Material, Gas Temperature and Power Deposition on Rates and Yields
Authors: Engelmann Yannick , Neyts Erik C. , Bogaerts Annemie
Published: July 2021

We developed microkinetic plasma catalysis models to investigate the plasma-assisted ammonia synthesis on transition metal catalysts in dielectric barrier discharge plasmas. These models aim at gaining insight in the reaction mechanisms and kinetics of plasma-activated species at the catalytic surface. We focus on the effects of vibrational excitations as well as plasma-generated radicals, on the turnover frequencies and equilibrium conversion.

Based on the results of DFT calculations, we built scaling relations for the catalytic conversion of N2 and H2 towards NH3on transition metal catalysts. These scaling relations allow the generation of ‘volcano’ plots that show the logarithm of the turnover frequencies as function of a catalyst descriptor (in our case the binding energy of N). We compare the volcano plots for thermal catalysis with vibrationally-enhanced catalysis and radical-enhanced catalysis in order to investigate how the plasma can most efficiently aid in the catalytic conversion. Careful analysis of reaction flow diagrams shows which pathways are dominant in each of the regimes. We show that Eley-Rideal (ER) mechanisms can become very important in plasmas with high densities of radical species as opposed to thermal conditions where ER is usually considered negligible compared to Langmuir-Hinschelwood. We determined on which catalysts ER mechanisms are most important and how they impact the turnover frequency.

This framework was introduced in a plasma chemistry model in ZDPlasKin to study conversions as function of catalyst material, gas temperature and specific energy input. Model results show the temporal behavior, with the specific role of microdischarge filaments and afterglows, of filamentary plasmas and how catalyst material, gas temperature and specific energy input can induce conversions beyond thermal equilibrium.
(Invited) A Continuous, Atmospheric-Pressure Plasma-Water Droplet Reactor for Nitrogen Fixation
Authors: Toth Joseph , Abuyazid Nabiel , Lacks Daniel , Renner Julie N. , Sankaran Mohan
Published: July 2021

Ammonia production via the Haber-Bosch process has a large carbon footprint due to the hydrogen gas feedstock. One possible solution is to use water as the hydrogen source in a process-intensified scheme whereby ammonia is produced by directly reacting nitrogen gas and water. Toward this end, we investigated a catalyst-free, atmospheric-pressure plasma process to continuously produce ammonia from nitrogen gas and atomized water droplets. Through several control experiments, the production of ammonia and other forms of fixed nitrogen were confirmed. By comparing water droplets versus water vapor as a feed to the reactor, it was discovered that the ammonia forms through gas-phase chemistry and the liquid phase does not appear to significantly contribute. By comparing hydrogen gas to oxygen gas and water as a feedstock, insights into the reaction mechanism were made. When hydrogen gas was used, no nitrates or nitrites were synthesized as expected, and the ammonia production was comparable to water, indicating similar mechanisms involving feedstock dissociation to atomic hydrogen may be occurring. When oxygen gas was used, no ammonia or nitrates/nitrites were detected, which suggests that water provides a unique reaction pathway for nitric and nitrous acid to form in the gas phase. Our study demonstrates that simple nitrogen gas and water droplets can serve as feeds in a plasma process for the sustainable and distributed production of ammonia or other fixed nitrogen compounds.
The Effect of Cation Doped ZnO Electron Transport Layer for Pure Blue Emitting Zntese/ZnSe/ZnS Quantum Dot Light Emitting Diodes
Authors: Choi Hyung Seok , Kim Yohan , Kim Jiyong , Geßner André , Wedel Armin
Published: July 2021

Colloidal quantum dot light emitting diodes (QLED) has considered as next generation display technology due to their accurate color information, high brightness, with low process cost, and potential flexible substrates. Red and green QLED achieved nearly the efficiency of theoretical limitation by optimizing quantum dot materials and device architecture with the tremendous efforts of many fellow researchers [1,2]. However, the authentic blue color QLED with high performance and high stability is yet remained as a obstacle for the commercialization. Herein, we report the fabrication of ZnTeSe based blue QLED device with multi shell quantum dots with very high quantum yield over >90% at 443nm with narrow FWHM of 15 nm. The peak wavelength of quantum dot could be tuned with the different Te/Se ratio of the core and the thickness of intermediate ZnSe shell. With the combination of zinc magnesium oxide (ZMO), which is the most common electron transport layer (ETL) for blue QLED, and our highly luminescent blue quantum dot, bright blue QLEDs with the max luminance of 700 cd/m2 in the inverted structure are demonstrated. Moreover, to obtain the better-performed and stable electron transport layer, different cations such as lithium, nickel, aluminum, cerium, erbium and indium-doped zinc oxides were successfully synthesized and studied. we have analyzed the band gap of ZnO can be fine tuned by doping of different cations and the effect of different zinc oxide in the device will be tested in the further study. According to the recent researches of the device stability of blue QLED [3,4], inferior stability of blue QLED is originated from the interface of ETL and quantum dots. I believe that the study of various ETL materials can give us a key to solve the poor lifetime problem of blue QLED.

Reference

1. Li, Y., Hou, X., Dai, X., Yao, Z., Lv, L., Jin, Y., & Peng, X. (2019). Stoichiometry-Controlled InP-Based Quantum Dots: Synthesis, Photoluminescence, and Electroluminescence. Journal of the American Chemical Society, 141(16), 6448–6452.

2. Won, Y.-H., Cho, O., Kim, T., Chung, D.-Y., Kim, T., Chung, H., ... Jang, E. (2019). Highly efficient and stable InP/ZnSe/ZnS quantum dot light-emitting diodes. Nature, 575(7784), 634–638.

3. Chen, S., Cao, W., Liu, T., Tsang, S.-W., Yang, Y., Yan, X., & Qian, L. (2019). On the degradation mechanisms of quantum-dot light-emitting diodes. Nature Communications, 10(1), 765.

4. Kim, T., Kim, K.-H., Kim, S., Choi, S.-M., Jang, H., Seo, H.-K., ... Jang, E. (2020). Efficient and stable blue quantum dot light-emitting diode. Nature, 586(7829), 385–389.
(Invited) Optical and Electrical Property of Self-doped Silver Chalcogenide Colloidal Quantum Dots
Authors: Jeong Kwang Seob
Published: July 2021

Colloidal quantum dots have been used in various research fields such as display, bio-imaging, therapy, detectors, etc. Mostly, the bandgap electronic transitions are used to convert the light to electrical signals or vice versa. Not only the bandgap transition, but also the other electronic transitions are available under certain conditions , which is a merit of the quantum materials. The intraband transition, recently demonstrated in steady state, also can be used for various applications. To utilize the intraband transition, the quantum dots should be self-doped and the doped state should last even under ambient conditions. This talk will focus on optical and electrical properties of self-doped silver chalcogenide colloidal quantum dots exhibiting mid-IR intraband electronic transitions in steady-state.
(Invited) Optoelectronic Application of Colloidal Quatum Dots in Infrared Beyond Si
Authors: Hwang Gyu Weon , Jin Jun Young , Park Taehwan , Jeong Tae Hoon
Published: July 2021

Among electromagnetic wave spectrum, infrared region has many attractive applications such as a LiDAR, optical communication, telecommunications, thermography, bioimaging, photovoltaics, and night visions. However, the expensive cost of epitaxial III-V semiconductors and the fabrication process hinders the widespread of the infrared technology beyond the silicon absorption range. Colloidal quantum dots have a great potential as an alternative materials for infrared detection. Lead chalcogenide QDs not only have tunable bandgap in infrared region but also have process compatibility with conventional Si ROIC in the device fabrication process, which remarkably reduces fabrication costs. The performance of photodetectors incorporating the lead chalcogenide QDs, however, is suboptimal and needs further improvement. One of the main factors limiting the performance of QD-based photodetectors is a high density of surface defects. QDs inherently have large surface-to-volume ratios and dangling bonds on the surface acted as trap sites. Various methods to reduce surface defects, such as thermal and ligand treatment, have been introduced; however, even after these treatments, QD-based photodetectors still show the relatively low detectivity (D*).

In this work, we demonstrate the various approaches to improve the performance of infrared photodetectors and their results. We focused on the reducing the trap density by the surface treatment of QDs using thermal annealing and chemical treatment in order to improve the device performance. We developed the chemical treatment method for reducing trap states with maintaining the existing ligands. Thermal annealing also can reduce the trap density; however, it sintered QDs by atomic diffusion. We found optimal condition for reducing the surface traps with suppressing sintering. The effects of these treatments were evaluated by the device performance and trap characterization. These approaches improve the bandwidth and the responsivity compared to reference devices. Moreover, we treated the surface of QD layers to show the interfacial effect on the QD devices.
(Invited) Electronic and Optical Properties of Si, Ge and Sige Low Dimensional Systems: Ab-Initio Results
Authors: Marri Ivan , Ossicini Stefano
Published: July 2021

In recent years,considerable efforts have been done to study silicon, germanium, and silicon/germanium slabs, nanocrystals, and nanowires for optoelectronics and photovoltaic solar energy applications. These zero- one- and two-dimensional systems, with sizes ranging from few to some tenths of nanometers, show unique electronic, optical, and transport properties that are intrinsically associated with their low dimensionality and to the quantum confinement effect. The possibility of understanding the microscopic properties of these systems and modulating their characteristics by doping and passivation can open new perspectives in the development of new, advanced, photovoltaics and optoelectronics devices. In this talk, we will discuss ab-initio theoretical results obtained by our group in the study of electronic, optical, and transport properties of silicon, germanium, and silicon/germanium low dimensional systems. The role played by size, passivation, and doping will be discussed. Moreover, we will show how the interaction between different nanostructures is a promising route to foster the establishment of third-generation photovoltaics.
Determination of Rate Equation for the Electrochemical Hydrogenation and Hydrogenolysis of Furfural in Acidic Media over Copper
Authors: May Andrew , Watt Steven , Biddinger Elizabeth J.
Published: July 2021

The use of electricity from renewable sources allows for carbon neutral electrochemical processes to be operated. One example process is that of the electrochemical hydrogenation and hydrogenolysis of furfural (FF) to furfuryl alcohol (FA) and 2-methylfuran (MF). FA is used as a reactant in making furanic polymers for molds and castings, and MF has been identified as a high octane fuel. The electrochemical reactions of FF to FA and MF occur in parallel in acidic conditions on Cu catalysts. In this work we investigated the reaction mechanism by proposing a set of elementary steps, deriving the corresponding rate equation, and fitting it to the data. A Langmuirian trend was seen in the production rate vs FF concentration data.

Experimentation was done using a catholyte that contained 0.1 or 0.5 M H2SO4 with a concentration of FF between 10 and 120 mM. The potential was first varied in pH 0 with 100 mM FF to determine the Tafel slope and exchange current densities, as well as the range of potential where the reaction is not mass transfer limited. The Tafel region of the system was found to be between -517 mV and -572 mV. To determine the effect of concentration of FF, the applied potential was set to -560 mV vs RHE, where the system is limited by kinetics and not mass transfer. The reaction rates to desired products were found to change from positive order to zero order with respect to FF concentration, showing a Langmuirian trend. It was found that the plateau in the reaction rate was 50% and 58% lower for MF and FA species respectively when the pH was changed from 0 to 1. The reaction rate equation was determined to be the equation that best fit the data across both pH levels.
Using Magnetic Fields to Intensify the CO2 Electrolysis Process
Authors: Bhargava Saket , Azmoodeh Daniel , Chen Xinyi , Cofell Emiliana R. , Esposito Anne Marie , Verma Sumit , Gewirth Andrew A. , Kenis Paul
Published: July 2021

Atmospheric CO2 concentrations measured at the ESRL (NOAA, Mauna Loa, HI) have risen to 413 ppm in the past 60 years as a result of addition of about 14.7 Gigatons of net CO2 to the atmosphere per year.1, 2 A fraction of the excess CO2 emissions can be utilized to synthesize carbon-based value-added chemicals (e.g.: CO, ethylene, ethanol) via the electroreduction of CO2 (ECR).3 Prior research efforts have resulted in active and selective catalysts for ECR, however, significant improvements in full cell energy requirement are still needed for ECR to be economically viable at industrial scales.4, 5 Some prior efforts have used magnetic fields as a process intensification tool to improve the electrochemical performance of water electrolysis.6

This talk will cover the use of magnetic fields in CO2 electrolysis to significantly reduce the full cell energy requirement in a gas diffusion electrode-based flow electrolyzer. We demonstrate that the application of a magnetic field leads to a reduction in cell potentials and/or increase in current densities, translating to an improvement in full cell energy efficiencies and reduction in full cell energy requirements. In a 2 M KOH solution, CO partial current densities of 468 mA/cm2 and 345 mA/cm2 were obtained at -3 V cell potential in the presence and absence of a magnetic field, respectively, corresponding to full cell energy savings exceeding 35% due to the application of a magnetic field. A combination of polarization plots and Tafel slope analysis reveals that the reduction in cell potentials and/or increase in current densities is caused by an improvement in the mass transfer of the electroactive species in the electrolyte due to the magnetohydrodynamic effect.

References

IPCC, Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2013.

https://www.esrl.noaa.gov/gmd/ccgg/trends/, (accessed 17 December 2020).

O. S. Bushuyev, P. De Luna, C. T. Dinh, L. Tao, G. Saur, J. van de Lagemaat, S. O. Kelley and E. H. Sargent, Joule, 2018, 2, 825-832.

B. Endrődi, G. Bencsik, F. Darvas, R. Jones, K. Rajeshwar and C. Janáky, Progress in Energy and Combustion Science, 2017, 62, 133-154.

M. Jouny, W. Luc and F. Jiao, Industrial & Engineering Chemistry Research, 2018, 57, 2165-2177.

F. A. Garcés-Pineda, M. Blasco-Ahicart, D. Nieto-Castro, N. López and J. R. Galán-Mascarós, Nature Energy, 2019, 4, 519-525.
Low- and Zero-Cobalt Layered Oxide Cathodes for Lithium-Ion Batteries
Authors: Manthiram Arumugam
Published: July 2021

Lithium-ion batteries have become an integral part of our daily life, powering portable electronic devices. They are in the process of transforming the transportation sector through electrification. They are also being intensively pursued for grid storage of electricity produced from renewable sources. Cost, sustainability, and supply-chain issues are major considerations in employing lithium-ion batteries for electric vehicle (EV) and grid storage applications. In the case of EVs, energy density or driving distance between charges is a critical parameter as well. These considerations have created immense interest to reduce cobalt content or eliminate cobalt altogether in layered oxide cathodes. With this perspective, the research and development trend has been to increase the nickel content and lower the cobalt content in LiNi1-y-xMny-CozO2 (NMC) cathodes. For instance, the industry has been gradually moving from LiCoO2 with 100% Co to NMC-111 with 33% Ni and 33% Co to NMC-622 with 60% Ni and 20% Co to NMC-811 with 80% Ni and 10% Co. While the increase in Ni content offers both an increase in capacity and a reduction in cost, it is also met with serious technical challenges. As the Ni content increases beyond 60%, the cathodes suffer from poor cycle, thermal, and air stabilities. The problems become exponentially challenging as the Ni content increases. This presentation will focus on improving the cycle, thermal, and air stabilities through compositional and controlled synthesis approaches, while reducing the Co content significantly as well as eliminating it altogether to give low- and zero-cobalt layered oxide cathodes with high capacities.

The low- and zero-cobalt layered oxide cathodes are synthesized by a coprecipitation of the hydroxide precursors with appropriate doping, employing a tank reactor, followed by calcining with lithium hydroxide at optimal temperatures under a flowing oxygen atmosphere. As the Ni content increases, the calcining temperature and conditions need to be sensitively controlled to obtain high-quality samples. The presentation will particularly focus on the performance evaluation and a fundamental understanding of the degradation mechanisms with cathodes containing > 90% nickel, including LiNiO2. The electrochemical performances are evaluated with full pouch cells by pairing the cathodes with graphite anode. The bulk and surface instabilities are assessed by employing a suite of advanced analytical methodologies, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), time-of-flight – secondary ion mass spectrometry (TOF-SIMS), high-resolution transmission electron microscopy (HR-TEM), etc. before and after extended cycling of full pouch cells. The presentation will also focus on assessing and improving the air stability as well as thermal stability of various compositions. Approaches to realize capacity values as high as 220 mAh/g will be presented.
Electrochemical Coupled Mechanical Behavior in Single Crystalline Ni-Rich Cathode
Authors: Bi Yujing , Tao Jinhui , Wu Yuqin , Li Linze , Xu Yaobin , Hu Enyuan , Wu Bingbin , Hu Jiangtao , Wang Chongmin , Zhang Ji-Guang , Qi Yue , Xiao Jie
Published: July 2021

The long-range electrical vehicles need the stable and safe high energy cathode materials for next generation batteries. High energy Ni-rich cathode plays a key role in advanced Li-ion batteries, but it suffers from moisture sensitivity, side reactions and gas generation, especially when Ni content increases to more than 0.6. Single crystalline Ni-rich cathode is a feasible approach to address the challenges present in its polycrystalline counterpart by reducing phase boundaries and materials surfaces. However, synthesis of high-performance single crystalline Ni-rich cathode is challenging. Owing to low structure stability at high temperature, higher Ni content cathode materials require lower synthesis temperature, in contrast to high temperature and time consuming calcination condition are required to prepare oxide single crystals. Using molten salt approach with sintering agent, single crystalline was successfully synthesized with 3 um average particle size and presents stable electrochemical performance tested in graphite/NMC full cells at realistic conditions. Mechanical behavior was studied on the platform of single crystalline LiNi0.76Mn0.14Co0.1O2. Planar gliding and microcracking were observed and changed along with concentration gradient during lithiation and delithiation.
(Invited) Mass Transport and Storage in Li-Ion Electrodes: Bulk and Interfaces
Authors: Maier Joachim
Published: July 2021

The subject of batteries is the interconversion of compositional changes and outer electrical potential changes. In solids all compositional changes refer explicitly to defect chemistry. Point defects such as interstitial and vacancies enable ion transport, mass transport and represent the species affected by storage [1].

The contribution discusses the modes of storage (bulk and interfacial storage) [2], derives the respective theoretical charge/discharge curves and discusses transport kinetics. The latter follow from the defect chemical picture, too. As for storage (chemical capacitance) also for transport (chemical resistance) one may distinguish between bulk and boundary phenomena [3]. The defect-chemical description is shown not only to be the adequate description (superior to, e.g. lattice gas models), it also leads to a generalized picture of electrode and supercapacitive storage.

References

[1] J. Maier, Angewandte Chemie International Edition 52 (2013) 4998.

[2] C.-C. Chen, J. Maier, Nature Energy 3 (2018) 102.

[3] R. Usiskin, J. Maier, Advanced Energy Materials (2020) 2001455.
Influence of Amorphous-to-Crystalline Transformation on the Negative Thermo-Optic Properties of TiO2 Films
Authors: Park Honghwi , Jung Jaedong , Liu Mingyuan , Lee Sunghwan , Park Hongsik
Published: July 2021

Titanium dioxide (TiO2) has long been hailed in various optoelectronic applications, including metaphotonics and photovoltaics, on account of its high refractive index, low loss tangent, and excellent transparency at a broad range of wavelengths. In particular, due to the negative thermo-optic properties of TiO2, it has been also employed for the fabrication of temperature-insensitive optical devices (called, athermal devices) that can mitigate the optical-performance instability from temperature variations. When the temperature rises, the negative thermo-optic coefficient (TOC, dn/dT) of TiO2 can compensate the unfavorable increase in refractive index exhibited by widely used optical materials such as Si, Ge, and III-Vs, which have a positive TOC. To realize the TiO2-based athermal devices, it is important to establish strategies to engineer and enhance negative TOC of TiO2 with fundamental understandings of processing-structure-property relationships. In this study, we systematically investigate the structure-property relationship of atomic-layer-deposited TiO2 to identify governing factors that determines the negative thermo-optic property of TiO2, and we demonstrate negatively enhanced TOC values up to −2.30 × 10–4 /°C in the visible to the near-infrared regime via mild thermal budget processing. Structural characterizations based on x-ray diffraction and reflectivity, and temperature-dependent refractive index measurements based on spectroscopic ellipsometry prove that higher crystallinity of anatase TiO2 leads to greater negative TOC values, ascribed to the higher film density and lower porosity compared to amorphous or less crystalline states. Furthermore, a photoelectron spectroscopy analysis shows an amorphous relaxation process facilitates the overall TiO2 crystallization during annealing by altering the local coordination of Ti. In addition, according to the Prod’homme model and bandgap analysis, we also report that the negative TOC of TiO2 is more influenced by the volume expansion than the polarizability. The findings about structure and chemical properties governing the negative TOC of TiO2 for athermal applications may be of significant relevance to many photonic devices showing strong performance instability due to the high positive TOC of active materials.

Figure 1
(Invited) Quantum Dots and Superconductivity in Silicon Systems
Authors: Zwanenburg Floris Arnoud , Sousa de Almeida Antonio
Published: July 2021

Ge/Si core/shell nanowires are suitable candidates for electrically driven spin qubits, and for the creation of Majorana fermions [1]. In highly tuneable hole quantum dots [2, 3], we observe shell filling of new orbitals and corresponding Pauli spin blockade [4]. In nanowires with superconducting Al leads we create a Josephson junction via proximity-induced superconductivity. A gate-tuneable supercurrent is observed with a maximum of ~60 nA [5]. We identify two different regimes: Cooper pair tunnelling via multiple subbands in the open regime the device [6], while near depletion the supercurrent is carried by single-particle levels of a quantum dot operating in the few-hole regime [5,7,8].

Secondly, we create ambipolar quantum dots in silicon nanoMOSFETs. We investigate the conformity of Al, Ti and Pd nanoscale gates by means of transmission electron microscopy [9]. We define low-disorder electron quantum dots with Pd gates [10], and depletion-mode hole quantum dots in undoped silicon [11]. For the latter we use fixed charge in a SiO2/Al2O3 dielectric stack to induce a 2DHG at the Si/SiO2 interface. The depletion-mode design avoids complex multilayer architectures requiring precision alignment and allows directly adopting best practices already developed for depletion dots in other material systems. Finally, we have realized ambipolar charge sensing: we have fabricated a single-electron transistor next to a single-hole transistor, and tuned both quantum dots to sense charge transitions of the other quantum dot. Using active charge sensing the single-electron transistor can detect the few-charge regime in the hole quantum dot [12].

[1] C. Kloeffel et al., Phys. Rev. B 84, 195314 (2011).

[2] M. Brauns et al., Applied Physics Letters 109, p. 143113 (2016).

[3] F. Froning et al., Applied Physics Letters 113, p. 073102 (2018).

[4] M. Brauns et al., Phys. Rev. B 94, 041441(R) (2016).

[5] J. Ridderbos et al., Advanced Materials, 1802257, (2018).

[6] J. Xiang et al., Nature Nanotechnology 1, 3 (2006).

[7] J. Ridderbos et al., Physical Review Materials, 3, 084803 (2019).

[8] J. Ridderbos et al., Nano Letters 20, 1, p. 122 (2020).

[9] P. C. Spruijtenburg et al., Nanotechnology, (2018).

[10] M. Brauns et al., Scientific Reports 8, 5690, (2018).

[11] S. V. Amitonov et al., Applied Physics Letters 112, p. 023102 (2018).

[12] A. J. Sousa de Almeida et al., Phys. Rev. B 101, 201301(R) (2020).

Figure 1