bluuebunny/crossref_metadata_2025 huggingface dataset:
Garnet-Type Li7La3Zr2O12 / Lithium Metal Interface: Microstructure and Electrochemical Properties in Solid State Batteries
Authors: Schmieg Johannes , Müller Marius , Dierickx Sebastian , Szász Julian , Weber André , Ivers-Tiffée Ellen , Gerthsen Dagmar
Published: May 2020

All-solid-state lithium ion batteries may overcome safety issues in future energy storage systems, when a non-flammable solid electrolyte instead of a liquid electrolyte is applied. Garnet-type Li7La3Zr2O12 (LLZO) is an encouraging choice due to its high Li+ conductivity and its chemical stability against lithium metal [1]. However, low-resistance LLZO/Li interfaces are deteriorated by incomplete adhesion of lithium metal onto LLZO and by surface contamination [2]. The resulting inhomogeneous distribution of contact areas may be more prone to dendrite formation. Previous studies [3,4] indicate that LLZO/Li interface quality is significantly improved by metallic buffer layers.

In this study, we aim for a reliable preparation of low-resistance interfaces between solid electrolyte and lithium metal. At first, magnetron sputtering is applied to deposit an indium buffer layer of 50 to 500 nm thickness onto the polished and cleaned electrolyte surface. For cell assembly, lithium foil is put on both sides of an In-coated LLZO pellet and the test cell is heated to 220°C in argon atmosphere. After that, microstructure and electrochemical properties of the symmetric cells are analyzed. We improved cross-section sample preparation to inspect the quality of LLZO/In/Li interfaces over hundreds of µm. Scanning electron microscopy (SEM, cf. figure 1) confirms excellent adhesion between lithium and LLZO. We use a dry inert atmosphere during preparation, handling and transfer of our samples to avoid artifacts and sample degradation. The FEI Helios G4 FX microscope enables correlative SEM imaging by simultaneous acquisition of up to four different detector signals for interface topography and material contrast. Local chemical composition at the interface is analyzed by energy dispersive X-ray spectroscopy and electron-beam damage is minimized for SEM imaging by selecting optimum electron energies.

Electrochemical impedance spectroscopy (EIS) followed by data evaluation via the distribution of relaxation times (DRT) and equivalent circuit modelling [5] deliver the proportional contributions of grain, grain boundaries and interfaces to the total impedance of symmetric cells (Li/In/LLZO/In/Li). Interface microstructures and EIS measurements are correlated for samples with different buffer layer characteristics to allow targeted optimization. We compare the pristine state of the test cells to samples that have been cycled with different current densities.

References

[1] S. Ramakumar et al., Progress in Materials Science 88 (2017), 325-411

[2] L. Cheng et al., Physical Chemistry Chemical Physics 16 (2014), 18294

[3] W. Luo et al., Advanced Materials 29 (2017), 1606042

[4] C. Tsai et al., ACS Applied Materials & Interfaces 8 (2016), 10617−10626

[5] P. Braun et al., Journal of Electroceramics 38 (2017), 157-167

Figure 1
High Performance Metal Sulfide Electrode for Lithium Battery
Authors: Kalimuldina Gulnur , Nurpeissova Arailym , Adair Desmond , Bakenov Zhumabay
Published: May 2020

The energy crisis is reaching its critical point where the actions for its mitigation cannot be postponed any longer. Therefore, urgency for more powerful, more stable energy storage systems is making our society investigate different materials with various configurations. Conducted studies on electrode materials, in general, have shown the essential tendencies besides electrode material itself being morphology, microstructure and chemical composition [1]. One of the promising electrode materials for the next-generation lithium-ion batteries is metal sulfides, as they possess high electronic conductivity and relatively high theoretical capacity than that of LiCoO2. Nowadays, copper sulfide is attracting more researchers due to its wide range of stoichiometric composition (CuxS, x=1-2) and diverse application in energy devices [2]. Extensive studies have demonstrated the possibility for numerous copper sulfide synthesis methods such as hydrothermal and solvothermal methods, melt diffusion, mixed solvents method, chemical deposition, sol-gel method, spray pyrolysis (SP), microwave-assisted growth, chemical vapor transport, template synthesis, and electrodeposition [3,4]. However, all those methods are costly and time-consuming. In this study, is presented a simple and straightforward novel method of preparation of flower-like structured copper sulfide (CuxS) (Fig. 1) with excellent electrochemical properties and cycling stability. Detailed studies of the electrochemical reaction mechanism for the new composition of CuxS phase will be presented.

References

[1] G. Zubiab, R. Dufo-López, M. Carvalho, G. Pasaoglu, Renew. Sust. Energ. Rev., 89 (2018) 292-308.

[2] C. Feng, L. Zhang, Z. Wang, X. Song, K. Sun, F. Wu, G. Liu, J. Power Sources, 269 (2014) 550-555.

[3] G. Kalimuldina, I. Taniguchi, J. Mater. Chem. A, 5 (2017) 6937-6946.

[4] C. Feng, L. Zhang, M. Yang,. X. Song, H. Zhao, Z. Jia, K. Sun, G. Liu, ACS Appl. Mater. Interfaces, 7 (2015), 15726−15734.

Acknowledgements

This work was supported by the projects 091019CRP2114 “Three-Dimensional All Solid State Rechargeable Batteries” and 240919FD3914 “Self-charging rechargeable lithium-ion battery” from Nazarbayev University.

Figure 1
Photo-Electrochemical Etching of Single Crystalline β-Ga2O3 Thin Film
Authors: Choi Yong ha , Bae Jinho , Kim Jihyun
Published: May 2020

β-Ga2O3 is a next-generation semiconductor material having ultra-wide bandgap energy of 4.8 eV and excellent electrical properties. So it is expected to be suitable for various applications such as power electronics, solar-blind UV photodetectors and gas sensors. However, there are some issues to overcome in order for β-Ga2O3 to be commercialized. Among them, crystal defects are important factor that significantly affects device performance. Defects are formed intrinsically during the growth process, or caused by high-energy plasma ion during dry etching. It has been reported that the electrical characteristics are deteriorated in the device such as MOSFET and MISFET fabricated by inductively coupled plasma etching. Unlike dry etching, which can cause damage by plasma ions, wet etching is a damage-free process that uses a chemical reaction between the target material and etchant. In addition, wet etching may be used for removing defects by using the etching characteristic, which the chemically unstable defect areas are preferentially etched. However, β-Ga2O3 hardly reacts with etchant at room temperature, and has been reported to have etch rate of several tens of nm/min when acid etchant are used at higher than 100 °C.

In our study, we have tried to increase the etch rate of β-Ga2O3 and remove defects effectively by Photo-electrochemical (PEC) etching. PEC etching is a method that promotes the reaction by irradiated light having energy above bandgap and applied external bias. Single crystalline β-Ga2O3 thin films are cleaved in the [100] direction with mechanical force from single crystalline β-Ga2O3 substrate. Ti/Au was deposited to form Ohmic contact with β-Ga2O3 thin films. With the PEC etching method, we could etch at a lower temperature than conventional wet etching. In addition, it was confirmed that the etch rate can be controlled according to the external bias condition. The details of our experiment conditions and results will be presented at the meeting.
(Invited) Characterization of Thermal Effects in Wide Bandgap Semiconductor Materials and Devices
Authors: Graham Samuel , Hopkins Patrick E , Goorsky Mark S. , Khan Asif , Henry Asegun , Doolittle W. Alan , Luo Tengfei , Suga Tadatomo , Mu Fengwen
Published: May 2020

Wide bandgap electronics made from nitrides (e.g., Gallium Nitride (GaN)) and oxides (e.g., Gallium Oxide (Ga2O3)) are currently under development due to their potential to create some of the most advanced RF and power electronic devices in the world. However, the thermal response of these devices under applied electric fields can create large power densities (RF and power electronics) that must be understood. For many of these devices, the electrothermal response plays a strong role in both the acceptable operation or long-term failure and reliability of the devices. Thus, tools that can help elucidate these responses and provide a method to help design better devices is of critical need for this field.

In this talk we will discuss advancements in thermal characterization techniques that have allowed new insights into electrothermal behavior in GaN and Ga2O3 materials and devices. Specifically, a focus on the role of device architecture and material processing will be addressed. For GaN and Ga2O3 RF and power electronics, the role of thermal interfaces in the heat dissipation of both lateral and vertical device architectures will be discussed. We will cover aspects of semiconductor-semiconductor as well as metal-semiconductor interfaces and their roles in device thermal management. A highlight will be the use of plasma activated bonding to provide ultralow thermal resistance interfaces that allow for heterogenous integration of nitrides and oxides with high thermal conductivity substrates. Finally, we will discuss the implications of these effects on device behavior through experiments and modeling.
Fabrication and Characterisation of Silicide/3C-SiC/Si Contacts for Schottky Barrier Diode Application
Authors: Cherkaoui Karim , Duane Russell , Ward Peter , Blake Alan
Published: May 2020

Silicon carbide is a wide band gap semiconductor which presents excellent physical properties such as a high critical electric field strength which enables the realisation of efficient power devices [1]. The cubic silicon carbide (3C-SiC) polytype has been less investigated than the more popular hexagonal structure 4H-SiC. 3C-SiC has the advantage that it can be epitaxially grown on Si by chemical vapour deposition (CVD) [2] and presents properties suitable for achieving cost effective SiC power devices in the range 650V to 1200V. These 3C-SiC/Si substrates offer a promising alternative to the costly hexagonal SiC (4H-SiC) wafers and can also be used as template for the epitaxy of cubic GaN [3]. However, the presence of the Si substrate does limit the temperature available to anneal out the implantation damage generated by some device processing sequences.

This work investigates the properties of metal silicides as a potential Schottky contacts for high blocking voltage 3C-SiC/Si Schottky barrier diodes (SBDs). For this study, Ti and Pt silicide contacts are formed on the (100)3C-SiC surface. The influence of the silicide formation temperature (500oC-650oC) on the contact electrical properties is investigated in detail. Current voltage (I-V) and capacitance voltage characteristics (C-V) are used to evaluate the reverse leakage current and extract the Schottky barrier height as well as the concentration of electrically active dopants in the N type 3C-SiC/Si. The Pt silicide Schottky contact is found to present higher energy barrier height than the Ti silicide Schottky contact and this trend was confirmed by the associated improved reverse current in the Pt Schottky. This is a promising result as it suggests that the reverse leakage is not dominated by the stacking faults inherent to this material. Temperature dependent I-V characteristics are measured and compared to theoretical I-V curves to explore the mechanisms responsible of the reverse leakage. The effort towards high blocking voltage final SBD device requires excellent PN junction edge termination. In this work, to avoid the damage caused by Al ion implantation, the electrical properties of 3C-SiC/Si PN junction diodes fabricated by epitaxy of P type 3C-SiC layers on N type 3C-SiC/Si substrates are also investigated. The reverse current mechanisms in the PN junction and the Schottky are compared and the suitability of the PN for device termination is discussed.

[1] Kimoto, T., Cooper, J.A. Fundamentals of Silicon Carbide Technology: Growth, Characterization, Devices and Applications, Wiley, (2014)

[2] A. Severino, C. Locke, R. Anzalone, et al., ECS Transactions, 35 (6), 99 (2011)

[3] Okumura, H., Ohta, K., Feuillet, G., et al. Journal of Crystal Growth, 178 (1-2), 113, (1997)
Rapidly Thinning Silicon Carbide By Anodization
Authors: Kuo Stanley Ken-Hua , Jian Bill Po-Yen , Li Wen-Shuo , Hwang Yean-Ren , Lee Benjamin T. -H.
Published: May 2020

SiC is a semiconductor material used to fabricate electronic devices that can operate under severe conditions, such as high temperatures, and which have some advantages over silicon-based devices (for example, high frequency and high power). The hardness of SiC is quite high (Mohs=9.5) and strong chemically inert, making it difficult be thinned. Up to now, since the majority carriers of n-type SiC are electrons, its application is more extensive, but it is also more difficult to thin. An effective etching method is by the reactive ion etching (RIE) method, which may produce satisfactory results in a smooth surface. In addition, according to reports, an efficiently etching processing can be performed by a high temperature (>700 C) molten alkali metal hydroxide (for example, NaOH). However, the equipment cost, operation convenience and thinning speed of these etching approaches are not as well as electrochemical etching, i.e., anodization. However, n-type SiC is very difficult to be anodized because of the lack of electric holes which are the key species for etching. In our report, we used a wafer bonding processing to form a temporary p-n junction by jointing to a p-type silicon, so that minority carriers, electric holes, in the mated p-type silicon can easily transfer to the SiC surface via a bias, resulting in a HF-based electrochemical etching. By the processing, the n-type SiC can be quickly thinned. After thinning, the p-type silicon subatrate can be easily removed without the chemical contamination on the thinned SiC substrate.

Figure: The anodized surface of n-type SiC.

Figure 1
(Invited) Selective Area Etching and Doping of GaN for Power Electronics
Authors: Li Bingjun , Wang Sizhen , Han Jung
Published: May 2020

Gallium Nitride (GaN)-based devices are very attractive candidates for next-generation high-power applications, due to the intrinsic material properties. However, the lack of selective-area doping technique in GaN greatly limits the design flexibility and device performance. Implant or diffusion of dopants into GaN are currently being pursued. Additionally, attempts of selective-area etching by reactive-ion etching (RIE) followed by regrowth doping have been reported by many groups; most of them reported defective electronic interfaces with very leakage characteristics. It was determined that the presence of highly energy ions, reactive chlorine species, and ultraviolet photons in RIE tend to generate both surface and sub-surface damages. Here, we report an alternative method of selective-area etching to overcome this barrier. Tertiarybutylchloride (TBCl) is employed as an in-situ chemical etchant of GaN in MOCVD to create smooth trenches, and to remove plasma etching-generated damages on the surface. Regrowth is performed right after the TBCl etching without breaking the vacuum. Several key issues that will be discussed include 1) the exploration of etching parameter space, 2) comparisons among continuous, RIE-etched, and TBCl-etched regrown PN diodes, 3) selective area etching and doping, 4) nanoscale characterization of selective area doping by scanning probes and atomic probe topography (APT), and 5) the implication of anisotropy in selective area regrowth.

This work is supported by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000871 as part of the PNDIODES program managed by Dr. Isik Kizilyalli.
(Invited) Characterizing Defects in Semiconductors for Solar Cells and Understanding Their Impact on Device Performance
Authors: Rockett Angus A.
Published: May 2020

Solar cells are intrinsically sensitive to minority carrier properties and therefore to intrinsic and extrinsic defects. This talk presents an overview of the application of microchemical, microstructural, and optoelectronic characterization techniques to observe these defects and connect their optoelectronic effects to the defect chemistry. This is particularly important in highly ionic materials and in materials that are applied as polycrystals where self-compensation, defect complexes, impurities segregated at grain boundaries, and second phases are critical. Therefore the talk will concentrate on those types of semiconductors. Scanning probe techniques and capacitance-based methods are particularly useful as they can probe within an individual grain even when that grain is small. Modeling to connect the individual defects to device performances is also described.
Efficient MAPbI3 Perovskite Solar Cells Employing Sputtered p-Type NiOx Hole Transport Layer on Dependence of Oxygen Partial Pressure
Authors: Seok Hae-Jun , Kim Han-Ki , Lan Shuai , Yi Ahra , Kim Hyo-Jung
Published: May 2020

In this paper, the effect of NiO
x
thin film prepared by a radio-frequency sputtering process under different oxygen partial (Ar:O2 ratio) pressures on the photovoltaic properties of planar-type MAPbI3 perovskite solar cells (PSCs) was investigated. The electrical, optical, morphological, and structural properties of sputtered NiO
x
thin films deposited under varied process oxygen gas condition are scrutinized. In particular, this study demonstrates that the properties of NiO
x
thin film with Ni3+/Ni2+ ratio are dependent on process oxygen gas condition. The influence of Ni vacancies on the chemistry and electronic structure of NiO
x
thin films is investigated using X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The sputtered NiO
x
thin film with lower Ni3+/Ni2+ ratio exhibits appropriate conductivity, hole mobility, high transmittance, and uniform surface morphology as well as a preferred in-plane orientation of the (220) plane under pure Ar gas atmosphere. When 5% (Ar:O2=19:1) or 10% (Ar:O2=18:2) oxygen is injected during the process, the conductivity of NiO
x
thin films with higher Ni3+/Ni2+ ratio is higher, but at the expense of optical transmittance. Additionally, this work exhibits the effect of perovskite active layer crystallinity and device performance using sputtered NiO
x
thin film under different oxygen partial pressures (Ar:O2 ratio) as hole transport layer for PSCs. The power conversion efficiency (PCE) of PSC obtains the highest PCE of 15.74% at the optimized NiO
x
thin film under pure Ar atmosphere. Compared to that, the efficiencies of the PSCs using the NiO
x
thin films processed at 5% and 10% oxygen partial pressure is 4.17% and 1.39%, respectively. Therefore, this study elucidate the effect of NiO
x
thin films deposited under different oxygen partial (Ar:O2 ratio) pressures on the performance of PSCs.
Investigation of Thermal Effect on Reliability and Chromaticity Shift in QD-LEDs Displays
Authors: Lin Chen-Te , Chen Hsueh-Shih
Published: May 2020

In this work, thermal effect on reliability and chromaticity shift in quantum dots (QDs)-based light emitting diodes (LEDs) are investigated by long term lifetime test and IR thermal image. The results have suggested that the heat power generation during luminescence conversion process play a key role in the compatibility between QD and encapsulation resin, which is correlated to the blue luminescence intensity generated from LED chip and the QD luminescence intensity converted by QDs. The ligands detachment of QD at luminescence conversion process results in poor reliability of QDs and influence on the thermal load ability of encapsulation resin, whereas the condition of QD should be a dominant factor. It was also found that QD with thicker shell could prevented heat power generation since higher conversion efficiency and better stability, shown the better reliability of QD-LEDs and less chromaticity shift.
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.
Amalgams Anodes for Alkali Metal Batteries
Authors: He Guang
Published: May 2020

The dendrite issue and the associated cell degradation problems have proved to be a key challenge to the practical application of alkali metal anodes. We present a simple yet efficient approach to fabricate amalgam anodes that afford long-term stability cycling at practical current densities and capacities. The amalgam layer allows fast electron transfer as well as Li/Na/K migration at the electrolyte-electrode interphase, which significantly promote the cycling performance. In-situ optical microscopy analyses confirm the dendrite nucleation and growth can be remarkably suppressed with the amalgam-protected anodes. The prototype full cells demonstrate much improved rate and long-term cycling stability. These promising results provide new perspectives on the regulation of sodium electrodeposition and hence the elimination of the dendritic morphology for the practical development of alkali metal batteries.
Synthesis and Electrochemical Properties of a Si/SiOx Composite for Reversible Lithium Storage
Authors: Yang Hae-Ri , Kim Jae-Hun
Published: May 2020

With the rapid development of electric vehicles and advanced portable electronic devices, the demand for higher-energy-density power sources continues to rise. Among various powers sources, Li ion batteries (LIBs) have been used as the most important power source due to their high energy density, reasonable cost, and long cycle life. Currently, carbonaceous materials are used as commercial anode materials because of their good cycle performance. However, graphite anodes exhibit a limited reversible capacity (LiC6: 372 mAh·g–1), which cannot meet the requirements for high-energy-density LIBs. Therefore, development of high-capacity anode materials is critical. To increase the reversible capacity of an anode, Li-alloy type materials have been intensively studied. Among various materials, Si has attracted a lot of interest because of its high theoretical specific capacity (Li15Si4: 3580 mAh·g–1) and natural abundance. In spite of the high theoretical specific capacity, Si anodes cannot be commercially used due to some drawbacks. The drastic volume variation (~400%) of Si during repeated alloying/dealloying processes causes mechanical pulverization of the electrode. As a result, capacity fading usually occurs. To resolve this issue, various approaches have been applied such as the use of Si nanostructures and active/inactive composites. However, these methods usually required time-consuming and complex procedures, which were not suitable for mass production. In this study, we propose a new Si/SiOx composite by incorporating excess Si as a stable anode material for LIBs. This Si/SiOx composite was prepared through a simple high energy mechanical milling process. Si nanoparticles and silicon monoxide were used as starting materials. To further improve the cyclic performance, a carbon coating on the composite was performed. The prepared materials were investigated by various materials and electrochemical analysis tools. The obtained composite electrode exhibited not only high reversible capacity but also superior cycle performance.
A New P2-Type Layered Oxide Cathode Obtained By Electrochemical Ion-Exchange for Potassium-Ion Batteries
Authors: Yu Tae-Yeon , Sun Yang-Kook
Published: May 2020

K-ion batteries (KIB) have attracted considerable attention as a potential alternative to lithium-ion batteries because of their low cost and high energy density. However, their development and durability have been severely limited by the lack of suitable cathodes with high capacity and good cycle life. Here, we prepare a low-cost Mn-based layered oxide, P2-type K0.75[Mn0.8Ni0.1Fe0.1]O2 (P2-K0.75MNFO2), via an electrochemical ion-exchange process and demonstrate its excellent K storage performance as a cathode for KIBs. During the charge–discharge process, P2-K0.75MNFO2 can release and store considerable amounts (∼0.5 mol) of K+ ions without multiple phase transitions in the voltage range of 1.5–3.9 V (vs. K/K+), as verified by X-ray diffraction characterization and first-principles calculations. Owing to its highly stable layered oxide framework, P2-K0.75MNFO2 delivers a high reversible capacity of 110 mA h g−1 at 0.1C and exhibits an outstanding cycle retention of 70% over 200 cycles at both 1C and 10C. In addition, a full cell with P2-K0.75MNFO2 as the cathode and hard carbon as the anode demonstrates long-term cycling stability over 1000 cycles, illustrating the feasibility of a safe and practical KIB system.
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
Diphenyl Diselenide As SEI- Forming Additive for High Voltage LiCoO2/Graphite Battery
Authors: Kim Hyeong-Jin , Park Hyeonghun
Published: May 2020

Lithium-ion batteries are widely used due to its high energy density and long cycle life. Yet, there is a continuous demand for much higher energy density and power density to expand the application to the electric vehicles. As flagship electrode materials, LiCoO2 (LCO) and graphite have been used. Higher operating voltage increases energy density, so researchers have conducted developments to raise final charging voltage. However, LCO/graphite battery suffers from capacity decay due to the destruction of electrolyte and cathode material at high voltage operation (>~4.3 V) and graphite-electrolyte reaction. There is a lot of researches about the solid electrolyte interface (SEI) to improve the battery performance. Electrolyte additive to make better SEI layer is one of the effective ways. In this study, diphenyl diselenide (Ph2Se2) is used as additive to improve battery performance. Changing the concentration of additive (0 %, 0.1 %, 0.2 %, 0.4 %), the electrochemical characteristics of the LCO/graphite cell were analyzed by cyclic voltammetry (CV), linear sweep voltammetry (LSV), field emission scanning electron microscope (FE-SEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). At high voltage operation (4.4 V), rate capability and cyclic stability of the cell with diphenyl diselenide were improved. It was presented that diphenyl diselenide decomposed in the LCO surface. As a result, the SEI layers including diphenyl diselenide prevent a collapse of LiCoO2 crystal on the cathode and decrease the reaction of graphite with electrolyte on the anode.
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.
Nickel-Rich NMC Cathode As a Lithium Metal Battery with a Cylindrical Cell Type 18650
Authors: Tubtimkuna Suchakree , Sawangphruk Montree
Published: May 2020

The nickel-rich lithium metal oxide (e.g., LiNi0.8Mn0.1Co0.1O2; NMC) has been widely used in conventional lithium-ion batteries due to its state-of-the-art materials in terms of high specific capacity (280 mAh g-1). However, aiming to higher performances in the high capacity cell of 18650-cylindrical type is hindered by the limitation of conventional graphite anode. In this work, we used lithium metal as an anode material to produce the first NMC lithium metal battery. The use of lithium metal can break the capacity wall of graphite (372 mAh g-1) with higher in a specific capacity. Likewise, the cylindrical cell performances in terms of energy density are significantly increasing due to the lower in the density of lithium compared to graphite. Moreover, the charge storage mechanism, safety concerns, and electrochemical performances are systematically investigated. We hope that this work can provide constructive information about the effect of lithium metal in high capacity lithium metal battery cells.