bluuebunny/crossref_metadata_2025_split huggingface dataset:
Trapezoidal Well Structures for Improving the Light Efficiency in Algainp-Based LEDs
Authors: Oh Hwa Sub 
Published: May 2020

(AlxGa1-x)0.5In0.5P-based LEDs have a small conduction band offset that limits their electron confining potential.1 This weaker electron confinement subsequently leads to electron heterobarrier leakage in AlGaInP heterostructure LEDs, especially in short-wavelength devices, where a fraction of the electrons injected into the active region have a sufficient thermal energy to escape into the cladding layer. To overcome this problem, trapezoidal well structures are introduced in the active region in order to prevent carrier overflow and to gain a higher light output power (Pout). In the field of AlGaInP-based LEDs that emit a short peak wavelength at around 590 nm, however, the effects of the trapezoidal well profile in the active region on LED performance has yet to be systematically studied.
In this study, we investigate the behaviors of optical and electrical characteristics according to their trapezoidal well profile in the active region through the analysis of optical behaviors and device performances.
To investigate the optical behaviors according to the trapezoidal well shape, the sloped barrier (SB) is inserted between well and flat barrier (FB) and the thickness of SB (dSB) is changed from 2.5 nm to 10 nm. And, the FB thickness is adjusted from 15 to 0 nm to maintain the total barrier thickness 20 nm. The schematic diagram of MQW structures of a trapezoidal-shaped well is depicted in Fig. 1(b).
Fig. 2 shows the device performances having different sloped barrier profiles in the MQW LED structures. As the current is increased to 600 mA, the current-voltage (I-V) curves show different behavior according to the SB thickness. In Fig. 1(a) inset, the forward bias voltage at 350 mA decreases from 2.86 V to 2.62 V with an increase in the thickness of SB from 0 to 10 nm. Fig. 1(b) then shows the light output power (Pout)-current characteristics of LEDs on the dSB and the normalized efficacy of the same LEDs at 350 mA operating current is shown in the figure inset. As the dSB between the well and the barrier is increased from 0 to 5.0 nm, the normalized efficacy improves from 1.0 to 1.16 and the maximum Pout increases from 400 to 500 mA, though at a further increase of the dSB to 10 nm, the normalized efficacy degrades to 0.98.
Acknowledgment
This work was supported by a Korea Research Foundation Grant from the super-saving-LED convergence development project (20004475, Development of high power red micro light-emitting diode for full color RGB) funded by the Ministry of Trade, Industry and Energy, Korea.
Building a Robust and Conductive Solid Electrolyte Interphase on Li-Metal Anode for High-Performance Li-Metal Batteries
Authors: PARK Seongjin , Sun Yang-Kook 
Published: May 2020

For the first time, trimethylsilyl azide (C3H9N3Si, hereinafter denoted as TSA) is used as an efficient additive in a fluoroethylene carbonate (FEC)-based carbonate electrolyte solution. Along with an LiF-rich compound, the addition of 0.1 M TSA to the FEC-based electrolyte induces a conductive Li3N-rich solid–electrolyte interphase layer on the Li-metal surface and allows the formation of a dense Li-deposit morphology, suppressing the dendritic growth of Li and improving the Li+ ionic conductivity. In a practical Li-metal battery using a 2 mol% Al-doped full-concentration gradient Li[Ni0.75Co0.10Mn0.15]O2 (Al2-FCG75) cathode, the TSA additive greatly improves the cycling stability and rate capability, even under practical operating conditions.
1. S.-J. Park, J.-Y. Hwang and Y.-K. Sun,J. Mater. Chem. A, 2019, 7, 13441-13448.
2. S.-J. Park, J.-Y. Hwang, C. S. Yoon, H.-G. Jung and Y.-K. Sun, ACS Appl. Mater. Interfaces, 2018, 10, 17985.
Determination of Possible Reversible Lithium Plating through Electrochemical Analysis at 30 °C in Lithium Ion Cells
Authors: Yourey William 
Published: May 2020

Fast charging of lithium ion cells is an important hurdle to overcome for the increased penetration of electric vehicles into the transportation market. During the fast charging of lithium ion cells with today’s current negative electrode active materials, namely graphite, lithium metal plating has a high likelihood of occurring. This occurs as most of the lithiated graphite potential is within 100 mV of Li/Li+ potential where a small polarization can result in lithium metal plating on the negative electrode. This plating leads to safety issues, and capacity fade, among other things. As the lithium metal is plated on the graphite negative electrode it can either become isolated and inactive, resulting in a loss of active lithium and capacity fade in the cell, or the lithium remains active during cell cycling where it may either migrate into the negative electrode over time or travel to the cells positive electrode during discharge.
To date most lithium metal plating identification techniques, involve destructive physical analysis. The current study presents an electrochemical approach and technique which may identify reversible lithium metal plating on graphite negative electrodes during fast charging of lithium ion cells.
High Entropy Oxides with Spinel Structure for Energy Storage Applications
Authors: Wang Syuan-Yu , Chen Han Yi 
Published: May 2020

To satisfy ever-growing energy demands in modern society, researchers are eager to synthesize functional and tailorable materials. In recent years, a new class material with the potential of exceptional properties, high entropy alloy (HEA), was discovered. Moreover, the concept of HEA has extended to the ceramic system, and a new class of oxide has been proposed, so-called high entropy oxide (HEO). In 2015, Rost et al. reported a equimolar oxide with a single rocksalt phase, (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O, and successfully proved that high configurational entropy is the driven force of stabilizing the structure at high temperature. Further studies regarding functional properties of (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O are also conducted, such as magnetic, optical, catalyst, and electrochemical properties. In 2018, Sarkar et al. have reported that (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O demonstrated outstanding cyclic retention and high capacity as anode material of lithium-ion batteries. Besides, they proposed that high-entropy effect resulted in good cyclic stability, and each cation presents in the bulk tailored electrochemical properties.
In this study, a spinel-structured HEO was first synthesized and characterized . Moreover, this spinel-structured HEO was utilized as anode material for lithium-ion battery and demonstrate high capacity (~500 mAh g-1), well cyclic stability with high coulombic efficiency (~100%) over 100 cycles. To investigate the storage mechanism of HEO, in operando X-ray diffraction and in operando X-ray absorption spectroscopy were utilized during charging and discharging. Even though there is no structural change, the valance state of each element changed obviously during lithiation and delithiation. Moreover, in operando transition X-ray microscopy investigation was conducted to observe the volume change during charging and discharging processes. Furthermore, the role of each element in energy storage was also investigated in this study. According to its cyclic stability, high capacity, and tailorable property, this spinel-structured HEO is a promising candidate for the energy storage in the future.
Induced Synthesis of a New Intermetallic NiSn5 Phase and Electrochemical Mechanism Investigation
Authors: Ying Hangjun , Han Weiqiang 
Published: May 2020

MSn5 (M=Fe, Co, Fe0.5Co0.5) are a series of metastable tin-based alloys discovered by Han’s group. Because of the high Sn content and high conductivity of alloying metals (Fe and Co et. al), the MSn5 phases exhibit superior electrochemical properties in lithium ion batteries. For example, 30-50 nm FeSn5 nanospheres can deliver a high capacity of 750 mA h g-1 at 50 mA g-1, and CoSn5 nanospheres exhibit good cycle stability up to 100 cycles. Although these three transition metals Fe, Co, and Ni show similar physical and chemical properties, we fail to synthesize NiSn5 phase by using the same polyol wet chemical method. In this work, we firstly synthesized the new NiSn5 intermetallic phase by adopting an induction synthesis method using Fe3+ and/or Co2+ as induction agent. Furthermore, the crystal structure was resolved using the charge-flipping method, and the growth and electrochemical mechanism were investigated using TEM and ex situ synchrotron XRD.
The resutl shows the NiSn5 phase belongs to tetragonal phase in P4/mcc space group, and has stoichiometric Ni atom defects, the actual chemical formula is Ni0.62Sn5. Growth mechanism study reveals that the FeSn5/CoSn5 seed crystal formed after addition of trace of Fe3+/Co2+ plays a vital role in the formation of NiSn5 phase. The existence of FeSn5/CoSn5 seed crystal can effectively reduced the nucleation barrier of NiSn5, and the NiSn5 nanospheres final form through Kirkendall diffusion. The phase evolution investigation reveals that the NiSn5 phase is irreversible after initial discharging/charging processes, unlike the reversible transformation of MSn5 (M=Fe, Co, Fe0.5Co0.5). This result accounts for the failure of NiSn5 synthesis using traditional polyol wet chemical method and the relatively low cyclability of NiSn5. We believe this method can be expanded to synthesize other new alloys which are difficult to produce using the traditional methods.

Figure 1 (a) The reaction mechanism of induced synthesis of NiSn5 phase. (b) Synchrotron XRD pattern and Rietveld refinement of NiSn5 phase. (c,d) TEM images of Sn and NiSn5 nanospheres.

Acknowledgments

This work is supported by the National Natural Science Foundation of China (Grant No. 51901206).

Figure 1
One Step Synthesis of Core@Shell Sige@Si Nanoparticles and Their Use As Active Material in High Capacity Anodes for Li-Ion Batteries
Authors: Haon Cédric , Desues Antoine , Herlin Nathalie , Boismain Florent , Coulon Pierre-Eugène , Soloy Adrien , Alper John 
Published: May 2020

In the frame of energy transition, silicon is a material of interest to develop Li-ion batteries with increased energy density. Nevertheless, the important volume change upon cycling (280 %) and reactivity towards electrolytes lead to rapid degradation of performances. Designing silicon-germanium structures is an efficient strategy to obtain stable performances of Li-ion batteries anodes. The synergetic effect of alloying silicon and germanium was demonstrated by Duveau et al [1], using micrometric particles obtained by ball-milling. The stability of the alloys was better than the stability of pure silicon and its capacity was higher than the capacity of pure germanium.
This work presents the one step synthesis of nanoparticles of Si-Ge alloys by laser pyrolysis using silane and germane as gaseous precursors. The average chemical composition of the powders (Si/Ge ratio) appears well correlated with the silane to germane ratio introduced in the reactor. Using STEM-EDX, an original SiGe@Si core@shell heterostructure is observed on these particles; the alloy is surrounded by a silicon shell. Using in-situ temperature measurements, we found that the temperature in the reaction zone is above the stability zone of the alloy and favors migration of chemical species to the surface. Varying the ratio between precursor gases led to the synthesis of various Si100-xGex heterostructures with x = 0, 20, 47, 77, and 100.
All the three alloy compositions were cycled at C/5 in coin cells vs lithium. The electrochemical performances outperform materials with similar compositions already published [1, 2, 3]. The capacity of all alloy compositions is higher when compared to germanium, whereas stability and coulombic efficiency upon cycling is better when compared to silicon. The best performances were obtained for Si53Ge47 with a reversible capacity of 1685 mAh.g-1 after 60 cycles.
Enabling Aluminum-Silicon Electrodes As Monolithic Anodes for Lithium-Ion Batteries
Authors: Tahmasebi Mohammad H. , Kramer Dominik , Zheng Tianye , Mönig Reiner , Boles Steven T. 
Published: May 2020

Based on current trends in lithium-ion battery (LIB) production and forecasts for immense demand of these energy storage devices, it is evident that all cell components will need dramatic improvement in the future. Although anode materials may be considered by some to be a lower priority, compared to cathode materials, the cost of the anode (and Cu foil current collector) comprise nearly 25% of the materials cost of a LIB cell, and consume ~30% of the volume. Among the possible alternative anode materials for LIBs to replace slurry-based graphite electrodes, alloying materials such as Si, Sn, Al and Ge are promising candidates. Despite the attractive advantages of aluminum-based electrodes (such as low cost, good geographic dispersity and high abundancy), capacity fade due to a large volume change associated with the α/β (Al/LiAl) phase transformation during cycling is the key problem. Al alloy or composite electrodes are a promising strategy for improving the reliability of Al-based electrodes. Among the Al-based monolithic anode materials for LIBs, to the best of our knowledge, Al-rich Al-Si alloys or composites have rarely been investigated.
The present work highlights a new achievement towards realizing monolithic, free-standing alloy anodes which can significantly reduce both the cost and processing complexity of LIB electrodes. Herein, we propose a novel strategy to enable the use of aluminum-silicon alloys as monolithic anodes for LIBs. Accordingly, the microstructural, morphological, and electrochemical evolution of Al-Si thin-films of various compositions were investigated, with a focus on understanding the process of Al-Si-Li ternary phase formation during lithiation (in the particular case of excess Al). Ex situ microscopy observations, along with comprehensive electrochemical analysis, suggests that remarkable performance can be achieved by controlling the electrochemical condition for the formation of Al-Si-Li ternary phase, such that no LiAl (β phase) forms during lithiation. In other words, Al-Si-Li ternary phase is cycled within a soft aluminum matrix, thereby avoiding the degradation associated with the de-/lithiation of the β phase [1].
[1] M. H. Tahmasebi, D. Kramer, R. Mönig, and S. T. Boles, “Insights into Phase Transformations and Degradation Mechanisms in Aluminum Anodes for Lithium-Ion Batteries,” J. Electrochem. Soc., vol. 166, no. 3, pp. A5001–A5007, 2019.
Mechanochemical Engineering of Polymer-Coated Silicate Nanocrystal Cathodes
Authors: Rasool Majid , Chiu Hsien-Chieh , Zhou Jigang , Zaghib Karim , Demopoulos George P. 
Published: May 2020

Lithium iron silicate has attracted a lot of attention due to its 330 mAh g-1 theoretical capacity (2 Li+ per formula unit). However, inherently it exhibits relatively poor Li-ion intercalation kinetics, interfacial reactivity and complex phase transitions resulting in lower than one Li+ storage and poor capacity retention. In this work, we report a core-shell strategy to overcome these obstacles making use of mechanochemical processing and polymer coating. Mechanochemical annealing has been sown recently [1] to lead to activation of Li-ion diffusion (DLi) by one order of magnitude enhancement. Subsequently, in situ conductive polymer coating was employed on the surface of nanocrystals via an ambient temperature chemical process. As a result of this integrated nanocrystal engineering approach the core-shell LFS@P (βII
) cathode material delivered >1.3 Li and substantially enhanced cycling stability.
[1] Rasool, M.; Chiu, H. C.; Lu, X.; Voisard, F.; Gauvin, R.; Jiang, D.; Paolella, A.; Zaghib, K.; Demopoulos, G. P., Mechanochemically-tuned structural annealing: a new pathway to enhancing Li-ion intercalation activity in nanosized βII Li2FeSiO4. J. Mater. Chem. A 2019,
7, 13705-13713
Impact of Nickel on Next-Generation Li-Rich Oxide Cathodes for Li-Ion Batteries
Authors: Ting Michelle , Burigana Matthew , McCalla Eric 
Published: May 2020

As developments in lithium-ion batteries have focused on improving energy density, cycle life, and reducing cost, an important class of layered oxides with excess lithium, Li[Li,Ni,Mn,Co]O2, has been heavily studied as a next-generation electrode material. However, our limited understanding of the underlying electrochemical mechanisms hinders our ability to mitigate the negative impacts of these mechanisms, preventing commercialization. Previous studies have shown that these materials show a myriad of simultaneous mechanisms including changes in the nickel oxidation state, reversible oxygen redox accounting for capacities exceeding the theoretical limit1, oxygen gas release decreasing cycle efficiency2, as well as structural transformations leading to voltage fade3. Due to this complex mixture of electrochemical processes, model systems have been used extensively to observe these processes one at a time.
This work on model systems is continued here by studying materials that show both nickel and oxygen redox but no structural transformations during cycling. This builds on work performed on Li-Fe-Sb-O and Li-Fe-Te-O where oxygen gas release was found to reduce Fe during charging of the electrode, an unexpected observation that had not been seen in other materials4. Given the use of nickel rather than iron in next-generation materials, herein we use Li-Ni-Sb-O and Li-Ni-Te-O as model systems to better understand the electrochemical contribution of Ni and O during cycling. The materials have been studied using extensive electrochemical tests, ex-situ powder X-ray diffraction, online electrochemical mass spectrometry, X-ray absorption near-edge spectroscopy and X-ray photoemission spectroscopy. Results show limited oxygen release from the particle surfaces only, coupled with a marked contrast between the nickel oxidation states at the surface (XPS) and those of the bulk of the particles (XANES). XPS data also demonstrates a slight reduction in surface nickel during oxygen gas release, confirming that the mechanism identified with Li-Fe-Sb-O does in fact occur in Ni-containing materials, though this is limited to the particle surface. Given that a great deal of work is currently being done to maximize the amount of nickel in next-generation electrode material, the consequences of nickel use in Li-rich oxides observed here are of high importance to further our understanding of the limitations of these materials that are currently preventing their commercialization.
1. McCalla, E. et al, Science
2015,
350 (6267), 1516.
2. Jung, R. et al, Journal of The Electrochemical Society
2017,
164 (7), A1361-A1377.
3. Gallagher, K. G et al, Electrochemistry Communications
2013,
33, 96-98.
4. McCalla, E. et al, Journal of the American Chemical Society
2015,
137 (14), 4804-4814.
Hard Carbon with Intensified Graphitization Induced By Graphene Oxide for High Initial Coulombic Efficiency Anode in Sodium Storage
Authors: Zhang Wenfeng , Zhang Huimin , Xiang Yu , Zhang Hao , Cao Gaoping 
Published: May 2020

Hard carbons hold the most promising practical application among all anode materials for sodium-ion batteries. However, the low initial Coulombic efficiency (ICE) limits their further commercialization. Herein, one kind of hard carbon with Intensified graphitization induced by graphene oxide was prepared by a new coupled carbonization strategy, in which the mixture of phenolic resin (PF) and grapheme oxide (GO) was heat-treated at high temperature directly. The as-prepared hard carbon exhibited outstanding electrochemical behaviors such as superior ICE. We also believe that the strategy may provide a constructive instruction for high performance hard carbon material designing.
For synthesis of hard carbon (GHCs), GO aqueous suspension was first prepared via a modified Hummer’s method. Then PF was dissolved in the GO aqueous suspension (mass ratio of PF:GO was 50:1 to 200:1). The slurry was cured and dried at 120 °C, and further carbonized above 1000 °C.
With increasing mass ratios of GO to PF, the interlayer distance of carbon decreased from 3.88 Å to 3.70 Å, less than 3.93 Å of pure PF, suggesting that the addition of graphene oxide may enhance the graphitization of PF derived carbon. La and Lc of GHCs also increased accordingly with the increasing of GO proportion, indicating the development of graphitic microcrystallite. C1s X-ray photoelectron spectra showed that, the sp2 C content of GHCs increased from 48.4% to 54.5%, which was several time larger than the pure contribution from physical addition of graphene theoretically (from 0.5% to 2%, corresponding to the mass ratio of PF:GO from 200:1 to 50:1 ). From HRTEM and SAED images, a signiﬁcant improvement of short-range ordering degree can be clearly detected with the increasing of GO content. Those results were so consistent, indicating that GO gives an effcient induced local graphitization in hard carbon.
The sodium storage performances of GHCs were characterized in a half cells with metal Na as the counter electrode, using 1.0 M NaPF6 in ethylene carbonate /dimethyl carbonate (1/1 in volume) as the electrolyte. As-prepared hard carbon delivered a superior ICE over 90%, high reversible capacity of 343 mAh/g and excellent cycling performance beyond 150 cycles with a capacity retention over 90%. This may be due to the characteristics of GHCs with less defective and lower surface area , especially with the Intensified local graphitization induced by graphene oxide.

Figure 1
High Capacity Retention of Batteries Using Scalable Micro-Structured Silicon-Polymer Composite As Anode
Authors: Niu Junjie 
Published: May 2020

The emerging demands in large energy storage for portable electronic devices and transportations are attracting more interest in developing next-generation lithium-ion batteries (LIBs) with a series of new electrode materials, thus achieving a 3-5 times higher capacity to meet a strategic perspective energy-density of 500 Wh/kg or higher. Silicon, with a theoretical capacity up to 4000 mAh/g, is considered as one of the promising anodes to achieve this goal. The industry R&D in Si-leaded anodes is widespread, and the release of commercial products for portable electronics seems imminent, although simultaneous achievement of high capacity and sufficient calendar life for automotive applications remains to be demonstrated due to a 360% volume expansion of silicon. The current ratio of silicon in graphite anode is less than 10%, which largely limits the overall energy density. The degraded battery performance and complex synthesis process of various nano-structured configurations pose challenges on mass production industry.
Here we present the improved battery performance using micro-sized silicon skeleton caged by polymer as anode, which was synthesized via a facile wet-chemical strategy (
ACS Nano
, 13 (2019), 12032-12041). The industry available, micro-sized AlSi alloy was used as precursor, which ensures a scalable production with low cost. The hollow skeleton configuration provides sufficient spaces to accommodate the drastic volume expansion/shrinkage upon charging/discharging while the minimum amount of conductive polymer serves as a protective layer and fast channel for Li+/e- transport. The battery with the micro-silicon cage as anode displays an excellent capacity retention upon long cycling at high charge/discharge rates and high material loadings. The areal capacity of as high as >6.0 mAh/cm2 was obtained, which suffices a high battery energy density in powering large devices such as electric vehicles (EVs).