bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Point Defects and Doping in Ga2O3 and Related Alloys
Authors: Varley Joel Basile
Published: May 2020

Ga2O3 and related alloys are a promising platform for realizing wide-band gap semiconductors for use in a number of next-generation electronic devices exploiting their large band gaps and controllable electrical conductivity. Ga2O3 exhibits a band gap (4.8 eV) that can be tuned by In and Al incorporation, with Al-containing alloys increasing the band gap in contrast to In incorporation. While control over defect concentrations and n-type doping of Ga2O3 is rapidly improving, the dopability of alloys has remained largely unexplored. Here we describe the behavior of point defects and n-type dopants in Ga2O3 and consider the prospects of doping in the larger-gap Al-containing alloys using first-principles modelling approaches based on hybrid functional calculations. We consider a number of conventional dopants such as Si, Ge and Sn, as well as newer dopants that have been identified as effective alternatives. These results provide guidance for doping in Ga2O3 and related alloys incorporated into heterostructure devices.

This work was partially performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and partially supported by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. DOE, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office.
(Invited) Recent Advances in the Modeling of Strain Relaxation and Dislocation Dynamics in ZnSSe/GaAs (001) Heterostructures
Authors: Ayers John E , Kujofsa Tedi , Raphael Johanna , Islam Md Tanvirul , Wales James , Lindstrom Kevin , Song Yifei
Published: May 2020

In this talk we will describe state-of-the-art approaches to the modeling of strain relaxation and dislocation dynamics in ZnSSe/GaAs (001) heterostructures. Current modeling approaches are all based on the extension of the original Dodson and Tsao plastic flow model to include compositional grading and multilayers, dislocation interactions, and differential thermal expansion. Important breakthroughs in the last twenty-four months have greatly enhanced the utility of these modeling approaches in three respects: i) pinning interactions have been included in graded and multilayered structures for the first time, providing a better description of the limiting strain relaxation as well as the dislocation sidewall gettering; ii) a refined model for dislocation-dislocation interactions including jogging provides a more accurate physical description of compositionally-graded layers and step-graded layers; and iii) inclusion of back-and-forth weaving of dislocations provides a better description of dislocation dynamics in structures containing strain reversals, such as strained-layer superlattices or overshoot graded layers. We will describe these three key advances and illustrate applications of each to practical heterostructures.
Precipitation of Molybdenum Oxides in Supersaturated Zinc Oxide Thin Films
Authors: Chen Yijia J , Zhu Shen-how , Lin Tien-Chai
Published: May 2020

Zinc oxide thin films saturated with molybdenum were prepared by RF magnetron sputtering process using zinc oxide and molybdenum targets for the co-sputtering. The sputtering power for zinc oxide was kept constant while that for molybdenum was varied from 0 watt to 35 watt. We found that the molybdenum-doped zinc oxide thin film change their color from transparent to grayish color as molybdenum sputtering power increases. The color change of the zinc oxide film suggests that the molybdenum changes its valance state as the molybdenum sputtering power was varied.

A surprising finding about the study is the electrical conductivity increases and then decreases with molybdenum sputtering power. The increase of electrical conductivity should be attributed to the increase of donor concentration as more molybdenum atoms are incorporated. The decrease of conductivity, on the other hand, is not so well reported. Hall measurement study shows that the conductivity decrease is caused by decreased electron concentration. However, the electron mobility increases steadily with increased molybdenum sputtering power even though the electron concentration decreases. This is an indication that the electrical conduction no longer occurs through the molybdenum-doped ZnO grains.

We propose that the conduction changes from grains to grain boundaries as molybdenum sputtering power increases. It means molybdenum is precipitated at the grain boundaries and forms conducting channels besides zinc oxide grains. The high mobility conduction channel is desired for devices using electron transport layers in their structures. The electrochemical solar cells are one of the devices that may benefit from the finding of molybdenum-doped oxide. We would like to present the valance change of molybdenum along with the conduction behavior, and would also like to predict the band alignment between zinc oxide and molybdenum oxide in the molybdenum-doped zinc oxide thin films. X-ray diffraction, UV-vis spectrophotometry, and x-ray photoelectron spectroscopy will be presented to show the conclusion that the electron mobility increase was attributed to the grain boundary conduction.
MOF-Templated Metal Oxides Sensitized with Quantum Dots Heterojunction for Efficient Solar Fuels Generation
Authors: Shi Li , Daniele Benetti , Li Faying , Wei Qin , Rosei Federico
Published: May 2020

The separation and transport of photogenerated charges carriers are two of the most crucial factors that determine the overall efficiency of photoelectrochemical (PEC) systems. Various strategies have been exploited for achieving efficient charge separation and transfer. Among them, the design of semiconductor heterojunction has been shown to be one of the most effective approaches. Metal oxides, such as TiO2, are the among the most common materials for water splitting. However, the control of phase alignment and the interface structure remains a challenge. A promising solution is to use a template approach by employing metal-organic frameworks (MOF) which are of broad interest as a new class of organic-inorganic hybrid materials and have been intensely exploited in various fields due to their unique physical and chemical properties. Furthermore, common metal oxides, such TiO2 or NiO have limited absorption of sunlight due to their large intrinsic band gap (i.e. TiO2 anatase: 3.2 eV) which hinders effective use in solar water splitting. To extend the absorption range of the MOF-templated metal oxides in the visible and near-infrared range, we employed metal chalcogenide QDs as sensitizers.

In this presentation, for example, we explore a simple metal organic framework (MOF)-derived synthesis to obtain a controlled mixed-phase (anatase and rutile) of TiO2 nanoparticles, which retain the MOF crystal morphology. After sensitization with core@shell CdSe@CdS QDs, the mixed-phase TiO2 film exhibited a remarkable photocurrent of 10.72 mA/cm2 and long-term stability, with a retained value of more than 78.1% after two hours. Compared with commercial TiO2 films, the MOF-derived TiO2 film sensitized by core-shell CdSe@CdS QDs, showed an enhanced PEC device stability of +42.1% and PEC performance of +47.6%. The enhanced performance is due to the presence of mixed rutile/anatase phases, that creates a favorable band energy alignment for the separation of the photogenerated charges. The proposed photoanode based on MOF-derived metal oxide is an efficient strategy to improve the efficiency of the heterojunction-based PEC system for hydrogen generation. Furthermore, the combined use of QDs can extend the absorption range exploiting a larger part of the sun spectrum.

Figure 1
(Invited) Electrical Performance Improvement in 300mm Ge-Based Devices
Authors: Tapily Kandabara , Nakamura Genji , Consiglio Steven , Clark Robert D. , Newman Daniel , Triyoso Dina , Niimi Hiroaki , Wajda Cory S. , Leusink Gert J.
Published: May 2020

As device feature size continues to scale, new device architecture and dielectric materials with engineered properties are becoming essential in overcoming the issues in scaled CMOS devices such as short channel effects. Some of the recent innovations device makers are exploring for better electrostatic control and improved performance are the introduction of new device architecture such as gate all around devices (nanowires/nanosheets), and channel engineering such as high mobility channel materials (Ge and III-V). Ge is particularly attractive for use as a channel material for P-type MOSFETs due to its high hole mobility and Si VLSI high volume manufacturing (HVM) compatibility. However, there are couple significant remaining challenges to integrating Ge into 300mm Si VLSI HVM which are a stable gate-stack formation and integration of Ge on Si (1-5). In this talk, advances in Ge gate stack engineering will be discussed. Using Si compatible technologies we have demonstrated scaled EOT by engineering both the interface and high-k formation.

Reference

1. S. Swaminathan, Y. Oshima, M. Kelly, P.C. McIntyre, Appl. Phys. Lett.,
95, 032907 (2009).

2. L. Zhang, M. Gunji, S. Thombare, P.C. McIntyre, IEEE Electr. Device. L., 34, 736 (2013).

3. C.H Lee, T. Nishimura, C. Lu, S. Kabuyanagi, A. Toriumi, IEDM, 32.5.1 (2014).

4. P. S. Goley, M. K. Hudait, Materials, 2301 (2014).

5. Q. Xie, S. Deng, M. Shaekers, D. Lin, M. Caymax, A. Delabie, X-P Qu, Y-L. Jiang, D. Dedytsche, C. Detavernier, Semicond. Sci. Technol. 074012 (2012)
(Invited) Quantum Multi-Body Interactions in Semiconducting WSe2 and C60-Graphene Hybrids for High-Performance Photodetectors
Authors: Kaul Anupama B , Bandyopadhyay Avra S , Jayanand Kishan
Published: May 2020

In this work we will discuss the use of halide-assisted low-pressure chemical vapour deposition (HA-LPCVD) with NaCl to help facilitate the growth of monolayer WSe2 at low growth temperatures of ~ 750oC, which is lower than the typical temperatures needed with conventional CVD for realizing 1L WSe2. Moreover, we experimentally probed the quantum multi-body interactions in 1L WSe2 ascribed to excitons, trions and other localized states by analyzing the temperature-dependent photoluminescence spectra. A 1L WSe2 based photodetector was fabricated using Al contacts, which shows a high photoresponsivity, and the interface state trap density of the Al/WSe2 junction was computed to be extremely low. Hybrids of two-dimensional (2D) graphene with fullerene (C60) molecules were also fabricated using electrophoretic deposition, where the C60 clusters are electrically charged upon the application of an external bias in a polar solvent. A low energy shift in the Fermi level EF
~ 140 meV was calculated for the hybrids. When the hybrid devices were irradiated with a broadband white light source and a tunable laser source (with wavelength λ ranging from ~ 400-1100 nm), a strong photoresponse was evident, in contrast to the bare graphene devices which appeared unresponsive. We will discuss the strong photo-response of the C60-graphene hybrids reported here which we attribute to the doping enhancement arising in the graphene upon the adsorption of C60.
Optimized SrVO3/Ag/SrVO3 Multilayers As High Transparency Electrodes for UV Optoelectronic Devices
Authors: Kim Su-Kyung , Seong Tae-Yeon
Published: May 2020

GaN-based ultraviolet(UV) LEDs are important for their use in various applications such as space-to-space communications, curing, sterilization, etc. For these applications, the development of high-efficiency UV LEDs is needed. However, UV LEDs show relatively lower external quantum efficiencies than visible LEDs. To enhance the performance of UV optoelectronic devices by increasing light extraction, it is essential to develop p-type transparent conducting electrodes (TCEs) with high transparency in the UV region. Sn-doped indium oxide (ITO) is typical material for transparent conducting electrodes (TCEs) because of its low resistivity (< 10-4 Ω·cm) and high transmittance (> 85%) in the visible range. However, ITO has large light absorption below 400 nm wavelength and the poor electrical properties when it is thinner than 50 nm. Thus, there is a need for alternative TCEs that have high transmittance in the UV light region (200 – 400 nm). Extensive studies have been conducted to develop TCEs such as graphene, CNT, metal nanowire, and oxide/metal/oxide (OMO) multilayer. Among them, the OMO structure can be a good candidate for TCEs, because the mid-metal layer acts as a conduction path and the oxide layers can lead to zero reflection conditions.

In this study, we used SrVO3 films to develop UV-transparent multilayer and investigated their structural, optical, and electrical properties as functions of SrVO3 and Ag thickness by means of UV-VIS spectrometer, Hall-measurement, and transmission electron microscopy. Unlike ITO film, SrVO3 films exhibited high transmittance (> 80%) up to 320 nm. It was shown that the SrVO3 film showed larger optical bandgap (4.3 eV) than that of ITO (3.7 eV). For the OMO structures with Ag thickness of 15 nm, the sheet resistance was in the range 2.76 – 3.15 Ω/sq, depending on the SrVO3 thickness. In particular, SrVO3 (25 nm)/Ag (15 nm)/SrVO3 (25 nm) sample exhibited the highest Haacke’s figure of merit (FOM) of 144.5 x 10-3 Ω-1 where the average transmittance of the OMO was 91.5% over the 360 – 400 nm wavelength. For the 25 nm-thick SrVO3-based OMO films, the transmittance and sheet resistance gradually decreased with increasing Ag thickness from 9 nm to 21 nm. For example, the sheet resistance of SrVO3/Ag/SrVO3 samples was in the range 1.97 – 6.48 Ω/sq and the transmittance varied from 82.6 to 95.5%. Among these samples, SrVO3/Ag (15 nm)/SVO sample showed the highest FOM value. Rigorous coupled-wave analysis (RCWA) simulations were performed to understand the measured transmittance behavior and zero reflection condition in the SrVO3/Ag/SrVO3 structure. These results imply that SrVO3-based OMO structure could be a potentially important TCEs for the fabrication of high-efficiency UV optoelectronic devices.
Mechanism of Reverse Leakage Current in Schottky Diode Fabricated on Large Bandgap Semiconductors like Ga2O3 or Diamond
Authors: Lau Wai Shing
Published: May 2020

The bandgap of Ga2O3 (4.5-4.9 eV) is larger than the bandgap of GaN (3.4 eV). In addition, single crystal bulk Ga2O3 wafers can be more easily manufactured than GaN wafers. Therefore, Ga2O3 has strong potential for applications in high power semiconductor devices [1]. Schottky diodes fabricated on n-type Ga2O3 have strong potential as fast high-power switching devices. Similarly, the bandgap of diamond (5.5 eV) is very large and diamond Schottky diodes have good potential.

For example, Harada et al. published their work on Schottky diodes fabricated on n-type Ga2O3 with PdCoO2 as the metal [2]. They claimed that their Schottky diodes have a very large Schottky barrier height of 1.8 eV. Other scientists using metals like W, Au, Ir, Pd or Pt cannot achieve such a large value of the Schottky barrier height. However, they did not propose any physical mechanism regarding the reverse leakage current in their Schottky diodes. One possible mechanism of reverse leakage current in Schottky diodes fabricated on n-type Ga2O3 is image force barrier lowering at the metal-Ga2O3 interface. Historically, there were 2 theories regarding the image force barrier lowering effect. In 1953, Krömer published his theory that the image force dielectric constant in the equation for Schottky emission should be equal to 1 [3]. Subsequently in 1964, Sze et al. published their theory that the image force dielectric constant in the equation for Schottky emission should be equal to n2 [4], where n is the refractive index of the semiconductor in the infrared or visible light range. The theory of Sze et al. quickly became the dominating theory whereas Krömer’s theory essentially became a forgotten theory. For Ga2O3, n is approximately equal to 2 [5] and so n2 is about 4. The author performed an analysis on the experimental data published by Harada et al. [2] and found that Krömer’s theory fit the experimental data from Harada et al. much better than the theory of Sze et al. Similarly, the author noticed that Krömer’s theory is better than the theory of Sze et al. for diamond Schottky diodes.

In conclusion, the author pointed out that it is necessary to resurrect an old and forgotten theory from Krömer in order to explain the experimental data on the reverse leakage current of Schottky diodes fabricated on large bandgap semiconductors like Ga2O3 and diamond.

References

[1] M. Higashiwaki, H. Murakami, Y. Kumagai and A. Kuramata, Jpn. J. Appl. Phys., 55, 1202A1 (2016).

[2] T. Harada, S. Ito and A. Tsukazaki, Sci. Adv., 5, eaax5733 (2019).

[3] H. Krömer, Zeitschrift fur Physik, 134, 435 (1953).

[4] S.M. Sze, C.R. Crowell and D. Kahng, J. Appl. Phys., 35, 2534 (1964).

[5] T. Onuma, S. Saito, K. Sasaki, T. Matsui, T. Yamaguchi, T. Honda, A. Kuramata and M. Higashiwaki, Jpn. J. Appl. Phys., 55, 1202B2 (2016).
Microstructure Control for Improving Swelling Behavior of Lithium Ion Batteries
Authors: Myeong Seungchoel , Park Keemin , Lee Kangcheon , Lee Seungwoo , Kim Sungmin , Song Taeseup
Published: May 2020

With the growing demands for high energy density of lithium ion batteries (LIBs), the electrode is thicker and denser to maximize the proportion of the active materials compared to the electrochemically inactive components such as current collectors and a separator. Accordingly, the electrode could lose the interconnection between pores and have reduced pore volume in the electrode, resulting in poor electrochemical properties due to the degradation of electrolyte permeability. Furthermore, the inhomogeneous volume changes of active materials in the electrode could cause the severe swelling issues in the thick and dense electrode system. Here, we report the thick and dense graphite anodes with the controlled pore distribution in the electrode to improve the electrochemical properties and secure the stable electrode swelling behaviors by two-step roll pressing. The uniform pore distribution in the electrode is confirmed by 3D X-ray microscopy (3D XRM). The graphite anode with the uniform pore distribution exhibits improved cycling performance (retention 85.83% @200cycle), and presents stable swelling behavior (4.47% @25cycles). We demonstrate that the improved electrochemical properties and stable swelling behaviors are realized in the thick and dense graphite anodes by facile two-step roll pressing.
Improved Performance of Si Nanowire Lithium Ion Battery Anodes By Au Catalyst Nanodot Formation on TiN.
Authors: Kim Dongheun , Crossley Kenneth , Ahmed Towfiq , Baldwin J. Kevin , Kim Yeonhoo , Li Nan , Pete Doug , Yoo Jinkyoung
Published: May 2020

While silicon (Si) is considered to be an excellent candidate for next-generation lithium ion battery (LIB) anodes due to its abundance and high gravimetric capacity, Si suffers from large volume expansion as a result of lithiation. Nanowires (NWs) allow for radial expansion and strain release. Due to this volume expansion, the formation of bulk-like Si structures during the NWs growth process significantly degrades battery performance. Here we report suppression of bulk-like Si formation by interfacial energy contrast between the NWs nucleation catalysts (spontaneously formed gold (Au) nanodots) and titanium nitride (TiN) films. The TiN film promoted a narrow distribution of Si NWs’ diameters and a direct electrical connection to the stainless steel current collector. The characteristics of the solid electrolyte interphase and lithiation/charge transfer mechanisms in Si NWs were also investigated using electrochemical impedance spectroscopy (EIS). The EIS data suggest that the impedance to lithium diffusion within the NWs is approximately 40 % smaller in the NWs grown on TiN than the NWs grown directly on stainless steel. LIB anodes fabricated with the Au-catalyzed Si NWs on TiN films displayed enhanced specific gravimetric capacities (>30 %) under diverse charge/discharge rates and significantly improved capacity retention over 500 cycles.
Inkjet Printing for Producing Li-Ion Secondary Batteries
Authors: Nakajima Satoshi , Kuriyama Hiromichi , Tanteitanton Porapon , Sagisaka Toshiya , Takeuchi Shigeo , Kanno Yusuke , Yanagita Hideo , Suzuki Eiko , Ushirogochi Toru
Published: May 2020

Recently, emerging devices such as IoT (internet of things) sensors and wearable devices require lithium-ion batteries (LIBs) with flexibility, various forms in terms of shape and size, and high power density. As required of these points, we have developed a new approach to producing free-designed cathodes and anodes for LIBs using inkjet printing.

In this study, we mobilized all our accumulated technological expertise, including ceramic particle grinding technology and high dispersion technology to develop a new printable dispersion liquid for electrode materials. Most types of cathode and anode materials have been successfully used to demonstrate high concentration and low viscosity dispersion liquid for an inkjet printing with high productivity.

The thickness of an inkjet printed electrode can be controlled by the number of droplets landed on the current collector. Because of the digital tuning of the thickness, we can obtain a thinner electrode with high-power density than the one fabricated by the conventional coating methods.

In order to demonstrate the high-power usage of inkjet-printed electrodes, we fabricated a “R”-shaped prototype cell with capacity of 3mAh using common ceramic-type cathode and anode materials. As a result of the low impedance of inkjet-printed electrodes, the prototype cell can operate over 30C rate. This prototype cell had enough power to send data collected on temperature and humidity every five seconds via Bluetooth to a computer.
On the Importance of Incorporating Structural Heterogeneity of Porous Electrodes in LI-ION Battery Models: Pore Network Modelling a Way to MOVE Forward
Authors: Khan Zohaib Atiq , Gostick Jeff T.
Published: May 2020

Image processing of 3D tomographic images to extract structural information of porous materials has become extremely important in porous media research with the commoditization of x-ray tomography equipment to the lab scale. Extracted pore networks from image analysis techniques enable transport properties calculation for bigger domains at a very low computational cost, allowing substantial investigation of porous media. Consequently, they are being increasingly used to model Multiphysics transport processes in various energy storage devices like fuel cells and batteries, where the geometrical structure plays a vital role in electrochemical performance, but true pore-scale modeling is computationally infeasible.

Traditionally, pore network modelling has been used to find electrochemical performance of Li Ion batteries by investigating pore phase interconnectivity in carbon electrodes. The actual lithium ion electrode, however, consists of active material, carbon binder and electrolyte filled pore phase. The interconnectivity of these phases influences the effective transport properties and hence electrochemical performance of cathode material. The presence of carbon binder phase not only reduces the SEI layer between active material and electrolyte phase but also influences tortuosity and effective electronic conductivity in the pore and solid phase respectively. The present work uses a pore network modelling frame work to investigate the effect of carbon binder phase on Lithium Ion battery cathode. We used actual three phase, X-ray tomography image of NMC-811 cathode material and studied its electrochemical performance with and without binder phase. Unlike previous models which compensate the importance of carbon binder as electrical conductor by assuming high electronic conductivity of active material, this study considers actual values of conductivities in all phases. Moreover, the impact of nanoporosity in the carbon binder phase was also explored and found to enhance the reaction rate compared to solid binder. The reduction in computational time achieved using the pore-network approach was so significant that adding additional physics and transient conditions could conceivably be included to increase the accuracy of the model, thereby providing more realistic simulations and point to the true limiting processes. The developed pore network model opens a new avenue for modelling complex electrochemical systems with less computational cost, enabling simulation of bigger electrode domains while keeping structural heterogeneities of material.
Systematic Investigation of Electrolyte Formulations to Improve Low Temperature Performance of Graphite /LiNi0.8Co0.1Mn0.1O2 cells
Authors: Rodrigo U. Nuwanthi D. , Jayawardana M. D. Chamithri D. , Milien Mickdy , Payne Martin , Lucht Brett L.
Published: May 2020

Due to high energy and power density, Lithium-ion batteries (LIB) are the most widely used power source for portable electronic devices and electric vehicles. However, performance of LIB is limited by its operating temperature, calendar life and cycling stability. One of the biggest challengers for LIB in electric vehicles is poor performance at low temperatures. At low temperatures, increase in interfacial resistance results in delivering a low capacity and reducing the fast charging capability. Addition of electrolyte additives in electrolyte formulation is one of the best ways to enhance the performance of LIB at low temperatures. In this study, a systematic investigation of electrolyte formulations with a combination of additives, has been studied to improve the low temperature (25°C to -10°C) performance of Graphite /LiNi0.8Co0.1Mn0.1O2 coin cells.
Porous Silicon-Cobalt Silicide-Carbon Composites for Reversible Lithium Storage
Authors: Seo Hyungeun , Kim Jae-Hun
Published: May 2020

With increasing use of portable electronic devices and electric vehicles, demand for development of high-energy density rechargeable batteries is rising. To meet the market demand for long-lasting rechargeable batteries, energy density of Li-ion batteries (LIBs) should be increased. The energy density of batteries is determined by the capacities of electrodes. Carbonaceous materials have been used as negative electrodes (anodes) in commercial LIBs because of their low operating potential and reasonable cycle life. However, the theoretical capacity of graphite anodes is relatively low, which is 372 mAh g-1 for the fully intercalated LiC6 phase. To increase the capacity, different types of materials using alloying or conversion reaction should be developed. Li-alloy-based materials can store several Li ions with an atom by electrochemical alloying reactions and therefore, high capacity can be obtained. In particular, Si has a high theoretical capacity of 3580 mAh g-1 for Li15Si4 and low operating potential. However, serious capacity fading usually occurs because of huge volume changes during cycling and their low electric conductivity. To address this problem, many strategies have been developed through changes in materials design. For example, incorporation of carbon is the most famous method to solve the capacity fading of Li-alloy-based materials upon cycling. The existence of carbon in Si matrix can buffer the volume expansion of Si materials with increased electric conductivity, thus simultaneously improving both cycling and rate performance. Porous structure can be another strategy to relieve the volume expansion by using the internal pores. However, the process is generally time and energy consuming. In this study, we report a simple preparation process of porous Si-CoSi2-C composites as anode materials for LIBs. The porous composite was synthesized through cheap starting materials and cost-effective methods. Si, magnesium silicide, and cobalt oxide were mixed using high energy mechanical milling (HEMM). Then, a carbon material was incorporated by HEMM. To produce porous structure, MgO formed by HEMM was removed by a wet etching process. As a result, porous Si-CoSi2-C composites were prepared. These composites exhibited a reversible capacity of 1100 mAh g-1 and good capacity retention after 100 cycles. The porous structure and the amorphous carbon matrix alleviated the volume change to allow the enhanced electrochemical performance.
Design of Advanced Li2s/Graphene Composite Cathode for Li-S Batteries
Authors: Kim Hee Min , Sun Yang-Kook
Published: May 2020

A mixture of graphene and Li2S is pelletized by a volume reduction of 220% to synthesize a high energy density cathode for lithium−sulfur (Li−S) batteries. The compacted graphene/Li2S composite cathode, in addition to providing robust electrical pathways, drives Li2S metastable particles to metastable states (high-pressure polymorphs with a highly deformed mechanical state), triggering a spontaneous conversion of Li2S to S8 in the first charging process. This direct conversion resolves the long-standing problem of excess polysulfide formation during Li2S activation. Moreover, graphene sheets, tightly encapsulating the Li2S particles, effectively confine the active material in subsequent cycles to ensure unprecedented cycling stability at a high loading density for the Li−S battery. Here we show a major breakthrough in Li−S battery technology, providing the high energy density promised by the proposed technology while ensuring the required battery lifetime. Furthermore, successful operation of a pouch-type cell employing the pelletized graphene/Li2S composite cathode with a high loading level clearly demonstrates the convenience of scaling up the proposed pelletization of Li2S or S cathodes to a large-format Li−S battery.
Porous Si-C Composite As High-Performance Anode Material for Li-Ion Batteries
Authors: Yang Young Mo , Kim Jae-Hun
Published: May 2020

Li-ion batteries (LIBs) have received widespread recognition as power sources for various potable electronics, electric vehicles, and large-scale energy storage systems. To meet ever-increasing demand for energy storage, it is necessary to develop next generation anode materials with a high capacity. Carbon-based materials are widely used as anodes for LIB and however, the theoretical capacity for graphite (372 mAh g–1) is limited due to its intercalation chemistry. Si has been considered as one of the most promising next generation materials as LIB anodes to replace commercial graphite because of its outstanding theoretical gravimetric capacity of 3580 mAh g–1 (for Li15Si4 phase), which can be obtained through the electrochemical alloying reaction with Li ion. Currently, the main challenges for using Si-based active materials are structural transition, low electrical conductivity, and unstable solid electrolyte interphase (SEI) formation caused by the large volume change (~400%) during alloying and dealloying cycle and irreversible side reactions with electrolyte. The large volume changes lead to the pulverization of electrode materials, resulting in degradation of capacity upon cycling. To overcome these drawbacks, many researches have been performed and various strategies have been proposed in terms of structural aspects such as hollow sphere, core-shell structure, and porous structure. In this study, porous Si-C composites were prepared through a simple annealing method of commercial amorphous silica (a-SiO2) and magnesium silicide (Mg2Si). Then, a chemical wet etching process was performed to remove formed magnesium oxide (MgO) and a carbon layer coating was finally carried out. The prepared material exhibited high reversible capacity and good cycle performance with very high initial coulombic efficiency. The enhanced electrochemical properties can be attributed to the porous structure with thin carbon coating.
Study on the ‘Shape Change’ of Rechargeable Zinc Electrodes in Alkaline Electrolytes
Authors: Nakata Akiyoshi , Morita Masayuki , Ogumi Zempachi , Abe Takeshi
Published: May 2020

Zinc, the most historical material for battery application, is one of the candidates for the high capacity electrodes of the next-generation secondary batteries, and has been applied in Zn/Air, Zn/NiOOH. These zinc-based batteries commonly employ aqueous alkaline electrolytes that have some advantages such as high ionic conductivity for high rate capability and non-flammability for high safety, which are particularly attractive for the mobile and EV applications. However, their insufficient cycle life due to the deterioration modes such as zinc dendrite formation, densification and shape change, has limited the widespread use of the zinc-based secondary batteries. In particular, the shape change is known to be a serious problem, in which the active material is gradually lost at the edge and agglomerates in the center of the electrode in the course of cycling, resulting in the capacity fade.

For suppressing this undesirable redistribution of the zinc electrode, it is essential to clarify the growth mechanism of the shape change phenomenon. So far the growth mechanism has been studied and analyzed, especially in the view point of the reaction (current) distribution, by various methods such as direct visual observation, tracing radioisotope, monitoring current distribution with the use of divided electrode, and calculating mathematical model. As the shape change proceeds dynamically with charging-discharging cycles causing electrode composition changes, the detailed observation of the composition change of zinc species during the cycling offer fruitful information on the reaction distribution to understand the growth mechanism of the shape change precisely and key to improve it. In this study, we evaluate the distribution of zinc species in Zn/NiOOH cells to elucidate the way the shape change occurs in the course of cell cycling.

References:

[1] A. Nakata
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H. Arai
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H. Murayama
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K. Fukuda
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T. Yamane
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T. Hirai
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3D Printed Electrodes for Solid-State Lithium Batteries
Authors: Winch Nicholas P. , Cipollone Domenic , Yang Hui , Yang Feng , Sierros Konstantinos A. , Wu Nianqiang
Published: May 2020

Solid-State Lithium Ion Batteries are the future of lithium ion energy storage technology, showing increased theoretical capacity and safety compared to their liquid electrolyte counterparts. However, poor mechanical contact and high resistance at the electrode-electrolyte junction prevent their wider adaptation. Direct Ink Writing (DIW) is an effective tool for electrode printing due to its ability to quickly and uniformly fabricate high surface area patterns and complex microstructures, increasing interfacial contact with a polymer electrolyte and boosting performance. This project will focus on creating, testing, and optimizing cathodes designed for Solid-State Lithium Ion batteries consisting of LFP (LiFePO4) based ink directly printed onto an aluminum current collector. The project goal is to optimize the rheology of the ink, particle loading, and patterning which will result in cathodes with improved electrochemical performance while maintaining mechanical durability in a quick and reliable manner. As such, various three-dimensional microlattice patterns and particle loadings will be tested to determine which combination results in the best cathode. DIW of electrodes for solid-state batteries may hold the key for the development and manufacture of the next generation of energy storage devices, greatly impacting our ability to utilize and further adopt renewable energy sources.
Li2TiS3: Lithium Metal Sulphide Rocksalt As New Cathode Material for High Energy Batteries without Critical Materials
Authors: Peralta David , Celasun Yagmur , Benayad Anass , Colin Jean-Francois , Haon Cédric , Herlin Nathalie , Martinet Sebastien , Bloch Didier , Patoux Sebastien
Published: May 2020

Most of the current Li-Ion cathodes use cobalt/nickel-based layered oxides as active materials. Due to the increasing demand of these critical and scarce elements in the coming years, it becomes urgent to develop new materials based on abundant elements. In 2014, Sakuda et al. introduce new sulphide rocksalt materials which can deliver a capacity higher than 400 mAh/g at 2.2 Volts.1

In 2019, a project named Spider funded by the European Union's Horizon 2020 research and innovation programme started with the objective to develop and use these materials in Li-Ion batteries. Several synthesis methods have been evaluated to produce Li2TiS3 materials. High capacities are obtained with these materials but they suffer from a poor cycle life.

Several characterizations and experiments have been performed in order to obtain a better understanding of the material evolution during cycling. Ex-situ XRD are in good agreement with previous results reported by Sakuda et al. and we completed the investigation thanks to Ex-situ SEM and XPS characterizations.2 We highlight that the material is partially oxidized during the cathode manufacturing process which lead to a loss of the lithium content in the materials structure. Our conclusions will be helpful to overcome these issues.

References

(1) Sakuda, A.; Takeuchi, T.; Okamura, K.; Kobayashi, H.; Sakaebe, H.; Tatsumi, K.; Ogumi, Z. Rock-Salt-Type Lithium Metal Sulphides as Novel Positive-Electrode Materials. Sci. Rep.
2014, 4, 4883. https://doi.org/10.1038/srep04883.

(2) Sakuda, A.; Ohara, K.; Kawaguchi, T.; Fukuda, K.; Nakanishi, K.; Arai, H.; Uchimoto, Y.; Ohta, T.; Matsubara, E.; Ogumi, Z.; et al. A Reversible Rocksalt to Amorphous Phase Transition Involving Anion Redox. Sci. Rep.
2018, 8 (1), 1–6. https://doi.org/10.1038/s41598-018-33518-4.

Figure 1
Electrochemical Effects of Yttrium(Y) Doping on Rich-Nickel Cathode Materials for Lithium Ion Batteries
Authors: Liu Dan , Zhu Wei , Zhu Jian Xiao , Wang Li , Pen Ren Jun
Published: May 2020

Rich-nickel layered oxides are regarded as one of the most promising cathode materials for the next generation of high energy lithium-ion batteries due to its high discharge specific capacity. However, the practical application of the materials is limited by poor cyclic stability. In order to solve this severe problem, the spherical precursor Ni0.85Co0.075Mn0.075(OH)2 cathode materials are synthesized through co-precipitation, then Yttrium(Y) is added to synthesize high nickel layered oxides Li(Ni0.85Co0.075Mn0.075)0.98Y0.02O2 during crystallization by solid-state reaction at a certain calcination temperatures under oxygen atmosphere to improve the electrochemical properties of materials in this study. The microstructure, particle morphology and electrochemical properties of the materials are characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), constant current charge and discharge, cyclic voltammetry(CV), respectively. The XRD results show that both two samples are corresponding to the layered α-NaFeO2 structure with R3m space group, while the c/a ratio and the unit cell volume increased with the addition of Yttrium. As the unit cell size increases, the volumes of Li-ion transport pathways also increase, which further promote lithium diffusion rate in the channel and facilitate Li+ intercalation/de-intercalation. And the SEM results demonstrated that both precursor materials were spherical secondary particles formed by the aggregation of primary scale-like particles, and the particle size gradually decreased with the addition of yttrium. The CV determination results show that both materials have two pairs of redox peaks. Still ,the redox peak of the doped material is broader and without the sharpness of the original one. In addition to this, the doped sample exhibits the excellent electrochemical performance with first discharge specific capacity with 193.34 mAh·g-1 and capacity retention of 85.83% after 100 cycles at 0.5C, while the original material LiNi0.85Co0.075Mn0.075O2 has higher first discharge capacity of 195.86 mAh·g-1, and the capacity retention in the 100 cycles of original was only 78.06%. In a word, the results showed that Y-doping could significantly improve the cyclic stability of LiNi0.85Co0.075Mn0.075O2 due to it promoted the diffusion channel of Li+ and inhibited the side reactions between samples and electrolyte.

Figure 1
A Compromise between Grain Size and Surface Area: Implications for the Lithium Ion Battery Performance of TiNb2O7
Authors: Chung Woowon , Raju Thota , Bang Jin Ho
Published: May 2020

Titanium niobium oxide (TiNb2O7) has received a great deal of attention in lithium-ion battery (LIBs) because of its high theoretical capacity, environmentally benign nature, and good cycling stability. However, TiNb2O7 suffers from limited rate capability due to low Li+ ion diffusivity and poor electronic conductivity. To overcome these limitations, in this study, we designed a new synthesis route to prepare monodisperse mesoporous TiNb2O7 microspheres. Delicate control over annealing temperature offers a way to manipulate the grain size and specific surface area of TiNb2O7 microspheres. Our investigation revealed there was a compromise between these structural parameters the LIB performance of TiNb2O7 microspheres. High surface area is obtained at the expense of grain size, and hence electrical conductivity and ion diffusivity are influenced by these two factors in different manners, giving rise to an optimal condition for the best compromise. This highlights the importance of gaining a comprehensive understanding of the critical factors governing the electrochemical behavior of TiNb2O7 to establish a design principle for advanced electrode materials.
Electrochemical Preparation of Si Based Anode Material in Molten CaCl2
Authors: Choi Jong-Hyeok , Jin En Mei , Lee See Hoon , Jeong Sang Mun
Published: May 2020

Graphite, which is commercially used as anode material in lithium-ion battery (LIB), has a low theoretical capacity of 372 mAh/g, and therefore should be replaced by alternative material with high capacity for the toward vehicles and other applications. Not only that, the cost and environmental issues should be considered in the production of alternative materials. In this regard, silicon materials have received the extensive research interest due to their high specific capacity of 3579 mAh/g, a low lithiation reaction voltage plateau (vs. Li/Li+) and abundant sources. Unfortunately, Si electrode typically suffers from irreversible capacity fading during cycling from their volume expansion and low intrinsic electronic conductivity. Recently, development of nanostructural design with various morphologies, Si nanowires, Si nanoparticles, and porous structures has received attention as a promising way to solve these problems. Nanostructural design largely improve cycle life by providing a sufficient free volume to accommodate silicon electrode expansion. However, commercially utilization of Si electrode is still insurmountable owing to some critical issues such as high costs, poor scalability and hazardous precursors. Furthermore, nanostructure Si includes severe side reactions due to a large surface area, low tap density. Here, we simply use the SiO2+Graphite mixture as the starting material and synthesize Si@SiC@Graphite composite material through electro-deoxidation method applied with the FFC Cambridge process, a simple approach for the high-purity extraction of metals from solid oxides via molten salt electrolysis that is known to be energy-saving and environmentally friendly. The electro-deoxidation was carried out in a molten CaCl2 at 1123 K in cell voltage of 2.6 V and 2.9 V. As an anode material, the prepared Si@SiC@graphite composite resolves all of the aforementioned critical issues and shows 900 mAh/g after 300 cycles without capacity fading. Furthermore, we fabricated high tap-density Si@SiC@graphite powder (~ 0.76 g/ml) using a mechanical pressing method, resulting in a high capacity (> 3.0 mAh/cm2) at the large loading of cathode, verifying the successful design of stable electron transfer and high dense structure.
The Effect of 2,2,6,6-Tetramethylpiperidinyl-Oxide (TEMPO) As an Electrolyte Additive and Its SEI Formation on Mcmb-Electrode
Authors: Lin Shawn D. , Yohannes Yonas Beyene , Hwang Bing-Joe
Published: May 2020

The stable radical molecule, 2,2,6,6-tetramethylpiperidinyl-oxide which is commonly known as TEMPO, is well known for its unusual stability as a neutral radical. (1, 2) The use of TEMPO and its derivatives have been examined in secondary batteries, since the year 2000. It is mainly used to enhance cycling performance, as a fire retardant, or as an additive in lithium sulfur batteries. (3) The TEMPO molecules are also used as liquid electrolyte. (4) It can also be used as redox shuttles in lithium-ion batteries. (5) In terms of the protection offered for a length of overcharge, TEMPO molecules are among the best shuttle molecules. (3-5) Recently, Dagger et al. (6) investigated an electrolyte combinations including both flame retardant (FRs) and film forming additives (FFAs) in order to generate synergetic effects and create electrolytes with enhancement in safety and electrochemical performance. The synergy of the FR and FFAs gives an effective SEI, diminishing the electrolyte ageing effect and also elevation of the life-time of the cycled cells at elevated C-rates. Incorporation of 2% TEMPO as an additive into STD + 5% FEC electrolyte results in a modification of the MCMB-electrode SEI. The direct in-situ DRIFTS analysis of the electrolyte additive; TEMPO, give a substantial insight into the nature SEI-formation of the negative electrode. The beneficial effect from the TEMPO additive might be the suppression of the solvent/additive decomposition by quenching the radicals formed. The positive effect of TEMPO was explained by the formation of polymeric species like, poly (VC), polycarbonate and also ROCOOLi, Li2CO3 and alkyl phosphorous fluorides. The studies described herein demonstrate that MCMB-electrodes in STD + 5% FEC solution containing TEMPO additive can be utilized together with high voltage cathode. The CV and in-situ DRIFTS for the electrolyte contribution with TEMPO additive is shown in Fig. 1. The possible reaction mechanism with the presence of TEMPO additive is discussed.

Fig. 1. CV (left) and in-situ DRIFTS (right) recorded on MCMB-electrode of the electrolyte containing STD+5%FEC+2%TEMPO.

References

1. J. T. Weil, J. Van der Veen and H. Olcott, Nature, 219, 168 (1968).

2. M. Taggougui, B. Carré, P. Willmann and D. Lemordant, J. Power Sources, 174, 643 (2007).

3. C. Buhrmester, L. Moshurchak, R. Wang and J. Dahn, J. Electrochem. Soc., 153, A1800 (2006).

4. L. M. Moshurchak, C. Buhrmester, R. L. Wang and J. R. Dahn, Electrochim. Acta, 52, 3779 (2007).

5. C. Buhrmester, L. Moshurchak, R. L. Wang and J. Dahn, J. Electrochem. Soc., 153, A288 (2006).

6. T. Dagger, M. Grützke, M. Reichert, J. Haetge, S. Nowak, M. Winter and F. M. Schappacher, J.Power Sources, 372, 276 (2017).

Figure 1