bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimizing Middle of Line (MoL) Contact Cleaning to Preserve Tungsten (W) Integrity in Advanced Technology Nodes
Authors: Singh SherJang , Muralidhar Pranesh , Das Kakoli , Scott Silas
Published: February 2020

Most of the advanced technology node semiconductor device manufacturing has adopted the gate-last approach which utilizes a RMG (Replacement Metal-Gate) process. The gate last method prevents unnecessary thermal loading on the high-k gate material and the metal layers; typically induced due to high-temperature activation of the doping regions. In gate-last process, junctions are salicidized after RMG requiring a different patterning approach for the active regions, i.e. an additional TS (Trench Silicide) mask is used. Thus the contact to the active regions is split into two levels. First the TS is formed and filled with tungsten which is followed by conventional contact patterning. With the increased complexity of contact architecture, contact cleaning becomes more critical in preventing contact opens as well as in maintaining the structural integrity to eliminate risks of contact to gate shorts and trench fill (tungsten) erosion. In this work, an advanced cleaning process is developed based on the electrochemical compatibility and interactions between the chosen chemistry and exposed layers as well as contaminants to be removed. The cleaning efficacy in the trenches is verified by measuring contact resistance as well as particle/flake inspections. Tungsten integrity is verified with bright field microscopy and damage to inter layer dielectrics is monitored by measuring trench and contact critical dimensions. Other structural interactions were studied with TEM imaging. The new cleaning process yielded substantially higher number of functional die as compared to POR (Process of Record). This paper will detail and discuss the above mentioned mechanism and performance data.
Effect of Pre-Wet Cleaning Conditions on the Pad Oxide Thickness
Authors: Bhattacharyya Dhiman , Sampathkumar Sathya Priya , Prasad Jagdish
Published: February 2020

The thickness of the furnace grown pad oxide is limited by the balance between the bird’s beak effect and the stress induced crack of the silicon nitride. Absence of pad oxide can completely eliminate the bird’s beak effect; however it also introduces stress generated cracks at the Si and silicon nitride interface which ultimately degrades the transistors. Additionally, the silicon wafers are also cleaned by wet processes to remove any incoming contamination, surface particles and other defects before the growth of this pad oxide. Since this wet cleaning process directly affects the pad oxide thickness, it is important to understand how the pre-clean chemistries and process conditions control the oxide growth.

In this study, effects of temperature, process time and concentration of SC1 and SC2 cleaning chemistries are investigated. Furthermore, effect of removing native SiO2 by initial dHF treatment is also evaluated as one of the variables. A set of experiments were designed to evaluate the effects and interactions between these variables within wide windows. A difference of >2A in pad oxide thickness and >1nm in mean roughness of the silicon surface after the pre-wet clean were observed. For example, SC1 process at higher temperature always showed thicker oxide growth compared to room temperature SC1 when the SC1 process time was identical. This article provides a detailed understanding of how the growth of pad oxide can be affected by the pre cleaning process parameters.
Real-Time pH Monitoring of Ultra-Diluted Chemistry with a Micro-Sampling pH Monitor
Authors: Nakai Yoko , Miyamura Kazuhiro , Takagi So , Mori Yoshihiro
Published: February 2020

At wet cleaning and etching process in semiconductor manufacturing, several ppm of ultra-dilute ammonia is sometimes used. When CO2 dissolves into the ammonia solution, it changes to carbonic acid, and neutralizes ammonia solution. It means, CO2 dissolution leads to pH change and impact to process performance. In order to know the chemical condition, pH is one of the key parameters. From its principle, however, internal solution (KCl) of pH probe dissolves into sample solution and lead to contamination, so the sample needs to be drained after measurement. Schematic system of pH probe is shown in Fig.1.  Measurement using pH probe requires several tens to hundreds mL sample, so waste chemical amount and cost impact is significant.

In order to solve such problems, we developed a real time, in-situ use pH monitor. This monitor equips micro flow pH sensor, which samples 0.5 mL per one monitoring, minimum interval is 1 min, i.e. sample consumption is maximum 30 mL per hour, and it enables to obtain real time pH data.

Using this monitor, ca. 1ppm ammonia solution was continuously monitored at every 1 minute. Test system is shown in Fig.2. From 0 to 0.9 h, sample solution was bubbled with N2, from 0.9 to 1.9 h bubbled with air, then from 1.8 to 4 h bubbled with N2.  Monitor result is shown in Fig.3.

[0 to 0.9 h] bubbled with N2 gas, CO2 does not dissolve to the solution, and pH is kept stable.

[0.9 to 1.9 h] bubbled with air, pH drops from 9.3 to 7.0 approximately in 10 minutes, which is caused by CO2 dissolution from the air.

[1.9 to 4 h] bubbled with N2 gas again, pH value recovered because CO2 is put out.

In conclusion, micro-sampling pH monitoring system, it enabled to detect clear pH change of ultra-diluted ammonia solution caused by CO2 dissolution with real-time bases.

Figure 1
(Invited) Optimizations of p and n-Type Bi2Te3-Based Ternary Compounds By Ms-Pulsed Plating and Annealing Under Telluride Atmospheres
Authors: Nielsch Kornelius
Published: February 2020

In this work, a comprehensive study of thermoelectric chalcogenide materials is presented and the systematic optimization of n-type Bi2Te3, p-type Sb2Te3 and their ternary compounds is performed. Thermoelectric materials are synthesized by potentiostatic electrodeposition on Au/Pt and stainless steel substrates. The influence of the preparative parameters such as the composition of the electrolyte bath and the deposition potential is investigated in a nitric acid solution.

As a post-deposition step, the influence of annealing of the films is investigated. The use of a potential-controlled millisecond-pulsed deposition method improves both the morphology and the composition of the films.

For n-doped films, approximately -100 µV K−1 (Bi2Te3) and -130 µV K−1 (Bi2(TexSe1−x)3) are achieved. Power factors and ZT values for p-type and n-type ternary alloys of up to 1325 µW m−1K−2 (ZT=0.4) and 825 µW m−1K−2 (ZT=0.3) are realized, respectively. In conclusions, the thermoelectric perform have been improved by one to two orders of magnitude in comparison to previously electrochemical synthesized thermoelectric layers. Based on the electrochemical synthesis and subsequent balancing of the stoichiometry by annealing under Te atmosphere, have resulted in bulk-like power-factors.

Millisecond pulsed electrochemical deposition is also a quite flexible approach for achieving nanowires of ternary chalcogenide compounds, which are grown in nanoscale confined spaces. After the annealing in Te enhanced the transport properties, on single Bi2(Te1-xSex)3 and (Bix-1Sbx)2Te3 nanowires power factors of 3100 mW K-2 m-1 and of 1600 mW K-2 m-1 with nearly bulk-like properties are achieved, respectively. Furthermore, we present magneto-resistance measurements on the Bi2Te3 and Sb2Te3 nanowires, which show clear evidences of topological surface states.

The financial support by the German Ministry of Science and Educations (BMBF) and by the German Priority Program DFG-SPP 1386 on Thermoelectric Nanostructures is gratefully acknowledged: www.spp1386thermoelectrics.de
(Keynote) Silicon Photonics Technology for Optical Communications with High Bandwidth Density Requirements (1Tbit/s and 1,000 Gbit/s/cm²)
Authors: Menezo Sylvie , Pares Gabriel , Bernabe Stephane , Castany Olivier , Sciancalepore Corrado , Hassan Karim , Blampey Benjamin , Charbonnier Benoit , Harduin Julie , Messaoudene Sonia , Saeedi Saman , Emami Azita , Ben Bakir Badhise
Published: February 2020

As many applications emerge with the need for providing System-In-Package with optical I/Os, Silicon photonics technology shows great assets over other optical technologies:

- The integrations of all the optical functions required to establish an optical transmission link have been demonstrated (silicon based modulators and (de)multiplexers, integration of Ge/Si photodetectors and heterogeneous integration of III-V/Si lasers). The fabrication is achieved in CMOS fabs on 200 and 300mm-wafers.

- Besides the Si-Photonics technology enables the use of 3D assembling techniques for interconnecting the Silicon-Photonic Integrated Circuit (PIC) with its required driving Electronics (Electronic IC). Micro pillars can be used with ultra-low parasitics between the PIC and its companion EIC.

The talk will review how the Silicon photonics technology toolbox developed at CEA-Leti (including the photonic devices library and the 3D assembling techniques for interconnecting PICs and EICs) scales with transmission applications having denser integration requirements (Tbit/s-class transceiver with bandwidth density > 1,000 Gbit/cm²). The performances of several demonstrators will be presented (25Gb/s receiver and 16-QAM transmitter) made from hybridation of Si-PICs and CMOS Electronic ICs).
(Invited) Negative Capacitance Using Ferroelectrics for Future Steep-Slope MOSFETS
Authors: O'Neill Anthony
Published: February 2020

Effective negative capacitance has been postulated in ferroelectrics because there is hysteresis in plots of polarization-electric field. In future integrated circuits, the incorporation of negative capacitance into MOSFET gate stacks would reduce the sub-threshold slope, enabling low power operation and reduced self-heating. As a step towards meeting this challenge, effective negative capacitance is demonstrated at room temperature in metal-insulator-metal capacitors, where it is stabilized by the presence of a paraelectric material.

Steep slope MOSFETs are a priority research area, driven by the need for low energy CMOS. Gate capacitance places a lower limit on the sub-threshold slope. The consequence is that transistors need a larger applied voltage to be on and/or will leak current and so can never be fully switched off. This leads to increased power loss and heating as more transistors are crammed onto the same area of silicon, which limits component density. The concept of ferroelectrics displaying effective negative permittivity has led to the speculation that their inclusion in the gate stack of a MOSFET will reduce the sub-threshold swing, S, of CMOS devices below 60 mV/dec. For a gate stack comprising a thin ferroelectric layer on top of a thin SiO2 layer, the channel potential ψs can change more than the gate voltage Vg, thus providing a step-up voltage transformer and S < 60 mV/dec. If this can be engineered, it heralds a transformation of future integrated circuits (ICs), reducing the off-state current (Ioff) and/or supply voltage (VDD) which otherwise limits Moore’s Law as heat generated during switching cannot be removed. The idea has led to the search for unambiguous experimental evidence of negative capacitance in candidate ferroelectrics at room temperature as a step towards this ambition.

In this study, experimental evidence is presented to demonstrate effective negative capacitance at room temperature in thin films of the ferroelectric BaTiO3. The BaTiO3 is fabricated in a bi-layer stack in series with SrTiO3, which is paraelectric at room temperature. The Metal-Insulator-Metal (MIM) stack is formed on a SrTiO3 substrate and using SrRuO3 as the bottom conducting electrode, which is lattice matched to the substrate. As the BaTiO3 layer thickness increases then the total capacitance is seen to increase, which is consistent with the ferroelectric capacitance being negative. In each case the bi-layer capacitance exceeds the SrTiO3 capacitance alone. Any hysteresis behavior is absent from the capacitance measurements in these bi-layer devices. The present work demonstrates the feasibility of negative capacitance at room temperature using a lead-free perovskite ferroelectric of varying thickness. The robust material can be integrated into CMOS or included as a performance booster within innovative devices such as tunnel field effect transistors in order to realize a future low power technology.
(Invited) Silicene As a 2D Material Candidate
Authors: Vogt Patrick , Le Lay Guy , De Padova Paola
Published: February 2020

Silicene, a new Si-based 2D material with a graphene-like honeycomb structure, has attracted considerable interest, because its topology confers to it the same remarkable electronic properties as those of graphene [1]. Contrary to graphene, silicene does not exist in nature and had to be synthesized on a substrate material, such as Ag(111) [2]. In comparison to graphene, such silicene layers  might have a potential advantage of being easily integrated in current Si-based nano/micro-electronics offering novel technological applications. Only very recently the first silicene transistor was reported, based on silicene layers grown on a Ag(111) substrate [3]. 

In this talk the recent development in epitaxial formation of single layer silicene will be reviewed, including structural and electronic properties for different silicene and 2D-Si layers. Furthermore, the formation of silicene double-layer and multi-layer structures will be discussed [4]. Different structure models will be compared to experimental results in order to unveil the nature of these layered materials. Such a detailed understanding of single/multi-layer silicene structures and their formation is crucial in order to optimize the performance of future devices which are based on such layers.

We will also discuss the stability of single/multi-layer silicene upon heating and oxidation and look a possible modifications of silicene by adsorbates. It is expected that silicene can be functionalized this way, which could open a new way for the application of Si in electronic devices.   

1)    G. G. Guzmán-Verri and L. C. Lew Yan Voon, Phys. Rev. B 76, 075131 (2007); S. Lebègue and O. Eriksson, Phys. Rev. B, 79 115409 (2009); S. Cahangirov et al., Phys. Rev. Lett. 102, 236804    (2009).

2)    P. Vogt et al., Phys. Rev. Lett. 108, 55501 (2012); C.-L. Lin et al., Appl. Phys. Exp.
5, 045802 (2012); B. Feng et al., Nano Lett. 11, 3507 (2012).

3)    Li Tao et al., Nature Nanotechnology (2015).

4)    P. Vogt et al., Appl. Phys. Lett. 104, 021602(2014), P. De Padova et al., Appl. Phys. Lett. 102, 163106 (2013)
(Invited) Innovative Embedded Non-Volatile Memories: Flexibility and Reliability
Authors: Navarro Gabriele , Vianello Elisa , Molas Gabriel , Sousa Véronique , Perniola Luca
Published: February 2020

Conventional memory technologies are facing nowadays many challenges such as miniaturization limits and reliability issues. In the last years, 3D integration strategies showed how Flash memory can still dominate the stand-alone market in the near future, mainly driven by the increasing demand of data storage in portable applications. However, in a technology context in rapid evolution and differentiation, where the microcontrollers market is growing fast becoming more and more price sensitive, the embedded non-volatile memories (eNVM) represent a key element for rapid product customization. Moreover, if the parallel and fast computing is pushing the CMOS platform towards aggressive technology nodes, back-end-of-line (BEOL) memory solutions can represent a real compromise between performances and cost saving.

Innovative NVMs such as resistive ram solutions (e.g. Phase-Change Memory), recently showed how they can represent a real breakthrough in terms of increasing performances, power consumption lowering and cost reduction. This is also due to their CMOS-compatible fabrication, and easy BEOL integration. Material engineering and architecture optimization demonstrated how these technologies can even target extreme specifications required in such applications as industrial or automotive.

In this talk we present the main features of emerging resistive NVM solutions, and how target specifications can be satisfied by material tuning, architectures engineering and specific programming techniques.
Reduction of Dendrite Formation in Zn Electrodes By Controlled Pulse Electrodeposition
Authors: Garcia Grecia , Ventosa Edgar , Schuhmann Wolfgang
Published: February 2020

Great efforts have been devoted to extending the use of Zinc for secondary batteries due to its high energy density, abundance and environmental sustainability. Nevertheless, there are several drawbacks preventing the implementation of Zn electrode in rechargeable batteries. One of the major limitations of a reversible Zn electrode is the formation of dendrites upon cycling. The morphology of the electrode undergoes significant changes leading to the formation of metallic Zinc needles. In a battery, these dendrites can penetrate through the separators, resulting in short-circuit and reducing significantly the lifetime of the battery.

Several strategies have been proposed to address this issue, ranging from incorporating certain additives in the electrolyte, to the use of special separators as a physical barrier between electrodes. Here, we present a strategy to suppress dendrite formation based on controlling the electrodeposition using designed charge pulse profiles. Understanding and designing a suitable pulse profile requires a large number of experiments. In order to make this possible in a reasonable amount of time, high throughput evaluation of the influence of a chosen electrochemical pulse deposition profile on the morphology was carried out using a specifically designed Scanning Droplet Cell (SDC). The SDC offers the advantage of performing automatically many experiments in a short timeframe enabling the evaluation of a wide vari­ety of parameters that may affect electrodeposition of Zinc. The electroreduction of ZnO proceed via a two-step process. Zincates dissolved in the pores of the paste electrode are reduced to metallic zinc. Due to the consumption of zincates, ZnO dissolves in the solution. Therefore, controlling the very early stage of the formation and growth of Zn nuclei from the reduction of zincates allows the redistribution of the material during charge. In addition, diffusion limitation of zincates was considered as a key factor for controlling the electrodeposition of Zn. Finally, our study envisions the application of these pulse profiles in a three electrode prototype cell.

Figure 1
Alkaline Earth Metals As Anode for High Energy Rechargeable Fluoride Ion Batteries
Authors: Tho Thieu Duc , Fichtner Maximilian
Published: February 2020

With increasing demand on energy supply together with reducing fossil sources, many efforts have been put into the research and development of environmentally benign, high energy density and low-cost rechargeable battery systems as an alternative. Fluoride Ion Battery (FIB), which is based on fluoride ion electrochemistry rather than lithium ion (in case of lithium ion battery), has emerged as a potential alternative. The element fluorine possesses an outstanding potential compared to Li owing to its high electronegativity and, thus, electrochemical stability, relatively low weight, more natural abundance and comparably low cost. By choosing an appropriate pair of electrodes comprising metal fluoride and metal together with a suitable fluoride-containing electrolyte, a high voltage electrochemical FIB cells can be built [1, 2]. Recently the first proof of concept for rechargeable fluoride ion batteries based on all-solid-state setup has been demonstrated [2].

Alkaline earth metals have recently attracted much attention for their employment in energy storage technologies due to potentially high energy density, low cost and environmental friendliness. Hence, in this study Ca and Ba pure metals were chosen and tested as anode in rechargeable FIB system. CaxBa1-xF2 (x ~ 0.5), a highly ion conducting metastable fluoride compound, was selected and synthesized via high energy mechanical milling route as fluoride ion conducting electrolyte. Powder X-ray diffraction confirms the formation of solid solution and electrochemical impedance measurement of CaxBa1-xF2 shows ionic conductivity in the order of 10-4 S.cm-1 at elevated temperature around 200 0C, which is in agreement with earlier report [3]. The assembly of all-solid-state electrochemical FIB cells was carried out with Ca or Ba as anode, selected metal fluorides (BiF3, CoF3, and CuF2) as high voltage cathode, and CaxBa1-xF2 (x ~ 0.5) as electrolyte. The cells were assembled in the charged state and electrochemically tested at ~ 200 0C. Initial results showed that the specific capacities of Ca/BiF3 and Ca/CuF2 cells for the first discharge are about 260 mAh/g and 350 mAh/g, respectively. These capacities are about 86% (in case of BiF3) and 66% (in case of CuF2) of their theoretical specific capacities and higher than those of Ce/BiF3 and Ce/CuF2 systems reported previously [2]. Electrode analysis together with cycling behaviour reveal the fluoride ion transfer between anode and cathode, as well as the cyclability of alkaline earth metal based FIB system. Further structural and electrochemical characterization will be presented and discussed.

References

1.   N. I. Sorokin and B. P. Sobolev, Crystallography Reports, 52, 2007, 842-863.

2.   M. A. Reddy and M. Fichtner, J. Mater. Chem., 21, 2011, 17059-17062.

3.   A. Duvel, B. Ruprecht, P. Heitjans and M. Wilkening, J. Phys. Chem. C, 115, 2011, 23784-23789.
Variational Multiscale Modeling of Charge Transport in Li Metal Battery
Authors: Moradi Mohammadmoein , Liu Lin
Published: February 2020

Battery performance highly depends on charge transport phenomena. The length scale of battery charge transport modeling is from nanometers to millimeters, therefore it makes the computational modeling difficult to accomplish. Moreover, the charge transport is well known at macro-scale and is easy to examine but there is difficulty in understanding the phenomena at micro-scale. Hence there is need for a framework that not only predicts the performance at macro-scale but also couples micro-scale details (e.g., microstructure and electrochemical reactions). The variational multiscale method (VMM) can be utilized as a paradigm for deriving models and numerical methods capable of dealing with multiscale charge transport phenomena [1]. The VMM can be applied to a broad range of problems and applications like complex electrochemical systems (e.g., Lithium batteries). VMM modeling is one of the essential tools to ascertain varied features of a problem concerning multiscale charge transport phenomena. In addition, VMM can be utilized to investigate continuum-scale systems with tracking detailed, electrochemical dynamics at the micro-scale [2]. Thus developing a VMM modeling framework to investigate the aforementioned problem is of much importance for obtaining reliable computational simulation results.

We will focus on building a link between battery micro-scale details and battery continuum level performance via VMM. The basic idea is to decompose the battery electrochemical modeling ODE/PDE solutions into two separate solutions including fine and coarse scale contributions. Fine scale equations will be solved with regard to coarse scale residuals and then the solution will be eliminated from coarse scale equations. Consequently, modified coarse scale equations which include the effects of fine scale can be obtained [3]. We will validate our model against Li metal batteries experimental studies on charge transport. Employing VMM, we can obtain charge transport at different levels and we expect the simulation and experimental data show better accuracy than traditional continue level simulations.

Reference

[1] T.J.R. Hughes, G.R. Feijόo, L. Mazzei, J. Quincy, Computer Methods in Applied Mechanics and Engineering,
3-24, 166 (1998)

[2] S. Lee, The University of Michigan, 2011

[3] M.G. Larson, A. Målqvist, Computer Methods in Applied Mechanics and Engineering, 2313-2324, 196 (2007)
A Novel Titanate As Anode Material for Sodium Ion Batteries
Authors: Ma Xuetian , Chen Hailong
Published: February 2020

The concern regarding the availability and cost of lithium is raised owing to the fast growth of the markets for lithium ion battery (LIB) and other Li-chemistry based energy storage technologies, such as Li-Air and Li-S systems. Sodium ion battery (SIB) is considered as an alternative technology, due to the potentially low cost and abundance of sodium[1]. Yet many key components of SIBs, including cathode, anode, electrolyte, still require further improvement.

                 Here we report a new titanate compound as a promising anode material for sodium ion batteries. The compound was synthesized through solid state reaction. Powder X-ray diffraction (XRD) and refinement were applied to investigate the crystal structure. Electron microscopy was used to study the morphology. The electrochemical tests showed high first discharge capacity of >200 mAh/g and ~80 mAh/g reversible capacity in following cycles with good retention, as shown in Figure 1. Ex situ XRD was also performed for fully and partially discharged/charged samples to discover the cycling mechanism and possible reasons for the capacity decay of this material. The influence of synthesis conditions, including temperature, ball mill rate and carbon coating amount were also systematically investigated.

Figure 1
Improved Cycling Stability of Polypyrrole Coated NaTi2(PO4)3 As an Aqueous Na-Ion Anode
Authors: Mohamed Alexander I
Published: February 2020

Aqueous sodium ion batteries offer an economic method for large-scale energy storage demanded by current sources of renewable energy. Although NASICON type NaTi2(PO4)3 is an attractive anode material with high capacity and a low redox potential allowing for high voltage cells, it suffers from considerable capacity fade when cycled slowly and deeply. In this work polypyrrole has been introduced as a coating for NaTi2(PO4)3 through a high-energy ball-milling process. When too thick of a coating was applied no redox reactions from the NaTi2(PO4)3  were visible due to the poor Na+ diffusion through the polypyrrole. The as coated composites containing 5wt% polypyrrole showed much better capacity retention compared to the uncoated material, retaining 57% of the initial discharge capacity after 50 cycles compared to the uncoated material retaining only 10% of the initial discharge capacity.
New Layered Cathode Compounds with High Energy Density for Sodium Ion Batteries
Authors: Li Xin , Wang Yan , Wu Di , Liu Lei , Dacek Stephen , Ceder Gerbrand
Published: February 2020

We report a new layered Na(Mn0.25Fe0.25Co0.25Ni0.25)O2 compound with O3 oxygen stacking. It delivers 180 mAh/g initial discharge capacity and 578 Wh/kg specific energy density with good cycling capability at high cutoff voltage up to 4.5V. In situ X-ray diffraction (XRD) shows a reversible structure evolution of O3-P3-O’3-O’’3 upon Na de-intercalation. The atomic scale mechanism for its higher capacity is systematically studied by a combination of DFT simulation, TEM and in situ XRD experiments, through the comparison with all the previously reported layered cathode compounds. We further design new compound based on this understanding that pushes the initial discharge energy density beyond 600 Wh/kg.
A Nanostructured Cathode Material with Varied Chemical Composition for High Energy Density Sodium Ion Batteries
Authors: Hwang Jang-Yeon , Myung Seung-Taek , Chung Kyung Yoon , Belharouak Ilias , Sun Y.-K.
Published: February 2020

Lithium batteries currently dominate the secondary battery market because of their high energy and good power density.[1] Despite their feasibility, the mass production of such large-scale batteries would likely contribute to the future exhaustion of limited lithium resources. This concern has led us to look for alternative systems to replace current lithium-related chemistries. Because of sodium’s abundance in nature, sodium-based rechargeable batteries have recently received intensive attentions [2]Our prior works36,37, we suggested that the nanorod-structured full concentration gradient materials are beneficial in performing outstanding electrochemical properties and excellent safety in lithium-ion batteries system, because the dense rod assembly could minimize surface area contacting with electrolyte.[3] We introduce a new concept: a radially aligned hierarchical columnar structure (RAHC) in spherical particles with varied chemical composition from the inner end (Na[Ni0.75Co0.02Mn0.23]O2) to the outer end (Na[Ni0.58Co0.06Mn0.36]O2) of the structure.Using this concept, we suggest that an electrochemical reaction based on Ni2+/3+/4+ is readily available to deliver a high discharge capacity of 157 mAh (g-oxide)-1 (15 mA g-1), an excellent capacity retention of 80% (125 mAh g-1) during 300 cycles in combination with a hard carbon anode, and a reasonable rate capability of 132.6 mAh g-1 (1500 mA g-1, 10 C-rate). In addition, the RAHC electrode exhibits good temperature performance even at -20°C. The chemistry of the RAHC material, which utilizes the Ni redox reaction and minimizes the surface area contacting corrosive electrolyte, is responsible for the excellent electrochemical properties and the satisfactory thermal stability, which exhibits a main exothermic reaction at 293.5oC with low heat generation.

References

(1)   Scrosati, B. & Garche, J. Lithium batteries: status, prospects and future. J. Power Sources 195, 2419 (2010).

(2)   Stevens, D. A., Dahn, J. R. High capacity anode materials for rechargeable sodium-ion batteries. J. Electrochem. Soc. 147(4), 1271 (2000).

(3)   Sun, Y.-K. et al. Nanostructured high-energy cathode materials for advanced lithium batteries. Nat. Mater. 11, 942 (2012).
Fabrication and Testing of Bulk-Type Solid State Batteries Based on a Garnet Oxide Electrolyte
Authors: Anandan Venkataramani , Drews Andy
Published: February 2020

Li-ion batteries have become the preferred energy storage technology for automotive traction applications. Li-ion batteries have several advantages over competing technologies, including higher energy and power density. However, Li-ion batteries do not have sufficient energy density to provide the long (~500 mile) range that customers are accustomed to in a reasonable packaging volume. In addition, the flammable liquid electrolyte in Li-ion batteries presents safety concerns that must be carefully managed. Potential high-energy replacements for current Li-ion batteries are Li-S, Li-air and solid state batteries (SSB). Among these technologies, SSBs are the one technology offering both higher energy density and a significant reduction in safety risks over Li-ion batteries. In this study, the performance of a bulk-type SSB was evaluated. This cell was fabricated using lithium metal as anode, lithium lanthanum zirconium oxide (LLZO) as a solid electrolyte and LiCoO2 as cathode.

LLZO solid electrolyte was prepared using a solid state synthesis method. In this method, precursors were mixed well and calcined. Calcined LLZO was pressed into thick pellets, sintered and then sliced into thin (300 µm to 400 µm) sheets for cell testing. The measured ionic conductivity of these sheets was ~3 x10-4 S/cm. Composite cathode layers were fabricated by coating one side of several LLZO sheets with slurry containing LLZO and LiCoO2, which was dried and then sintered at various temperatures. After sintering, the other side of the LLZO sheet was attached to a lithium metal (anode) to form a solid state cell. The impedance contributions from the solid electrolyte, the anode/electrolyte interface and the cathode/electrolyte interface was determined for each cell using electrochemical impedance spectroscopy (EIS). EIS data showed that the main contribution to the cell impedances resulted from the cathode/electrolyte interfaces. Further performance and characterization studies are ongoing and its results will be presented at the meeting.
Structural Evaluation of Amorphous MoS3 Positive Electrode Active Materials in All-Solid-State Lithium Secondary Batteries
Authors: Matsuyama Takuya , Deguchi Minako , Hayashi Akitoshi , Tatsumisago Masahiro , Ozaki Tomoatsu , Mori Shigeo
Published: February 2020

Sulfur is an attractive active material for positive electrode because sulfur has a high theoretical capacity. High capacity of the batteries can be achieved by using active materials with a large content of sulfur. Low electronic conductivity is a drawback of sulfur. We thus focus on a transition metal trisulfides such as TiS3 with high electronic conductivity. Moreover, amorphization of active materials is potentially capable of achieving higher capacity and cyclability because of open and random structure in amorphous materials. Recently, we have found that amorphous TiS3 prepared by ball milling had better cyclability than crystalline TiS3 [1, 2].

   Very recently, we have reported that amorphous molybdenum trisulfide (a-MoS3) electrode active materials prepared by mechanical milling showed high reversible capacity (about 670 mAh g-1) for 60 cycles in the all-solid-state lithium batteries with Li2S-P2S5 electrolytes at room temperature [3]. However, the electrochemical reaction mechanism of a-MoS3 has not been identified yet. In order to improve the battery performance, it is important to understand the reaction mechanisms of a-MoS3 in the all-solid-sate lithium batteries. In this study, we investigated microstructures and morphologies of a-MoS3 electrodes before and after charge-discharge processes.

   a-MoS3 was prepared by mechanical milling of the mixture of molybdenum metal and sulfur. The obtained active materials were applied as a positive electrode to all-solid-state cells with sulfide solid electrolytes. Structures and morphologies of a-MoS3 electrodes before and after charge-discharge tests were analyzed by XRD, XPS, SEM and HR-TEM.

   The HR-TEM observations of a-MoS3 electrodes during the 1st discharge test revealed that the lattice fringes due to MoS2 layer structure disappeared gradually. After the 1st full discharge, the lattice fringes were not observed and the electron diffraction showed halo pattern. However, the lattice fringes like MoS2 were observed again after the 1st charge. These results of HR-TEM observations suggested that the reversible structural changes of a-MoS3 occurred. On the other hand, Li2S nano crystals were observed in HR-TEM image of a-MoS3 after the 10th discharge. The HR-TEM image after the 10th charge showed no lattice fringes of Li2S and MoS2. It is concluded that MoS3 after the 10th charge was completely amorphous.

Reference

[1] A. Hayashi, et al.,
Chem. Lett.,
41 (2012) 886.

[2] T. Matsuyama, et al.,
J. Solid State Electrochem.,
17 (2013) 2697.

[3] T. Matsuyama, et al.,
J. Mater. Chem. A, submitted for publication

Acknowledgment

This research was financially supported by ALCA-SPRING project.
High-Performance Non-Aqueous All-Organic Redox Flow Batteries
Authors: Wei Xiaoliang , Huang Jinhua , Zhang Lu , Xu Wu , Cosimbescu Lelia , Vijayakumar Murugesan , Liu Tianbiao , Liu Jun , Wang Wei , Sprenkle Vincent
Published: February 2020

Redox flow battery has been widely considered as a promising large-scale stationary energy storage technology to stabilize the power grid and promote integration of renewables. The unique cell structure enables separation of energy and power thus offering tremendous design flexibility for different E/P applications. The limited voltage window in traditional aqueous flow batteries narrows down the intrinsic energy capacity. Therefore, nonaqueous redox flow batteries are being pursued because of the wider voltage window of nonaqueous electrolytes.

The current nonaqueous flow battery research is focused on the flow chemistry study and redox materials development.1 Among them, all-organic flow batteries is an important type and use organic electroactive materials at both positive and negative sides, taking advantage of the structural diversity and tunability of organic materials.2However, the current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. Especially, development of suitable negative side redox materials is considered more challenging.

Here we report several high performance all-organic redox flow chemistries with cell voltages higher than 2V. These flow cell tests demonstrated remarkable cell efficiencies and high operational current densities that exceed those of most reported non-aqueous flow chemistries. A mechanistic study was carried out to gain fundamental understanding of performance degradation in these flow batteries, indicating that the chemical stability of the charged species in various supporting solvents and salts plays a critically important role in achieving decent flow cell cycling stability. This finding can serve as an important guidance for the selection and design of stable redox electrolyte systems. 

Figure 1. (a) Cyclic voltammetry (CV) and (b) cycling capacity of an all-organic flow chemistry based on 9-fluorenone (negative) and 2,5-di-tert-butyl-1-methoxy-4-[2’-methoxyethoxy]benzene (positive).3

Figure 1
Nanoporous Aramid Nanofiber Separators for Non-Aqueous Redox Flow Batteries
Authors: Tung Siu on , Thompson Levi T , Laramie Sydney , Zhang Ruilin , Kotov Nicholas
Published: February 2020

Redox flow batteries (RFBs) possess a unique combination of attractive attributes including decoupled power and energy storage capacities, low cost, and high efficiencies, and are promising for large-scale energy storage. A significant challenge in the development of high energy density, non-aqueous systems is the lack of selective membrane/separator materials. This paper describes a novel nanoporous separator based on aramid nanofibers (ANF) produced using a spin-coating, layer-by-layer technique. The multilayer structure yields 5 nm pores, enabling nanofiltration and high selectivities, in terms of the transport of species with differing sizes. Vanadium acetylacetonate (V(acac)3), a candidate for non-aqueous RFB electrolytes, was used as the model active species. It’s permeability through the ANF separator was an order of magnitude lower than that for Celgard 2325, a commercial separator while the support conductivities were comparable. The combined effect resulted in a doubling of the coulombic and energy efficiencies for cells using V(acac)3 based electrolytes. For asymmetric cells with solutions of V(acac)3 as the negative electrolyte and ferrocene as the positive electrolyte, a 60% improvement in coulombic efficiency was achieved using the ANF separator over Celgard. The results demonstrate the feasibility of using ANF separators for symmetric and asymmetric non-aqueous RFBs and encourages further development.
Evaluation of Carbon Foams and Membranes As the Cathode in Non-Flow Zinc Bromine Energy Storage Cells to Mitigating Liquid Bromine Convection
Authors: Biswas Shaurjo , Mohr Robert , Senju Aoi , Steingart Daniel A
Published: February 2020

Zinc Bromine (Zn-Br2) secondary batteries have been extensively studied as a low cost, fully rechargeable, high density energy storage system. However, large scale and widespread commercial implementation of this battery technology has been retarded due to two key limitations [1]: i) self discharging of the cell due to Br2 (l) convection and diffusion through the liquid electrolyte towards the Zn anode. ii) shorting due to zinc dendrite formation after multiple cycles of the cell. Zn-Br2 flow-cells alleviate these limitations by adding Br2 (l) complexing agents, and flowing electrolyte to improve Zn plating, [2] respectively, at the cost of cell resistance, battery efficiency, size, and capital costs.

In this work, we address the Br2 (l) convection issue by designing a simple, low cost non-flow Zn-Br2 cell without the use of expensive complexing agents, via modification of the bromine cathodic electrode material composition and geometry. The Zn dendrite issue is addressed elsewhere [3]. We take advantage of the difference in density of the Br2 (l) (~3.1g/cc) and a 2M ZnBr2 electrolyte (~1.5 g/cc) to contain the liquid bromine below the cathode while cycling the cell. First, we demonstrate a thin membrane electrode composed of carbon black/graphite/PVDF having a density of 1.88 g/cc. The densities are matched such that the membrane electrode floats at the interface between the dense Br2 (l) and the electrolyte. During charging bromine forms and drops below the semi-porous membrane electrode while the cathode rises, reducing the anode-cathode spacing and, hence, the cell resistance. During discharge the Br2 (l) is prevented from convecting through the electrolyte by the physical membrane barrier, while allowing a small degree of diffusion. Second, we also demonstrate the use of highly conductive carbon foam bromine electrode, which selectively traps the non-polar Br2 (l) in its highly porous structure and thus addresses the bromine convection issue. The electrochemical characteristics of the non-flow Zn-Br2 cell based on both these bromine electrodes designs are discussed in terms of cell resistance, specific capacity, energy and coulombic efficiencies, energy storage capability and cycle life. The physical properties of the membrane and foam electrodes are analyzed using SEM, AFM and XRD.
Novel Long Cycle Life Room Temperature Sodium-Sulfur Batteries
Authors: Kohl Michael , Althues Holger , Kaskel Stefan
Published: February 2020

Sulfur is natural abundant, cheap, non-toxic and has about seven times the electrochemical capacity of standard Li-ion battery cathode active materials (1672 compared to 250 mAh g-1), considering the conversion to S2-.[1] Due to likewise low costs and high reactivity towards sulfur, sodium poses as an optimal candidate for the cell reaction with sulfur.

Since the 1980s sodium sulfur batteries are used as commercial stationary energy storage systems. They consist of a sodium negative electrode, a sulfur positive electrode and a β''-alumina solid electrolyte in between.[2] Due to low ion conductivity of the materials, this battery type has to be heated to temperatures above 300 °C, resulting in safety challenges related to molten sodium and to increased operation costs. To take advantage of the low cost nature of sodium and sulfur, while avoiding its downsides, sodium-sulfur batteries driven at room temperature are aspects of today’s research. One of the largest differences is the use of liquid electrolytes in room temperature cells, in order to ensure sufficient ion conductivity.

However, first reports on room-temperature Na-S-cells indicate significant challenges related to a parasitic reaction of dissolved sodium polysulfide species limiting the coulomb efficiency, the specific capacity and cycle life of this system (so-called polysulfide shuttle).[3]

In this work, electrolyte composition, sulfur/carbon composite cathodes as well as anode materials were tailored to result in room temperature sodium-sulfur batteries with significantly reduced polysulfide shuttle. Electrolyte additives were identified being able to enhance the cell efficiency and increase the sulfur utilization through a redox mediation mechanism. This cell chemistry enables discharge capacities of 1000 mAh g-1 as well as improved capacity retentions exceeding values from recent literature.[3+4] Our results demonstrate the feasibility of stable and low cost sodium-sulfur batteries at room temperature enduring over 1000 reversible charge / discharge cycles.

References:

[1] X. Ji, L. F. Nazar, Nat. Mater., 2009, 8, 500–506.

[2] Z. Wen, Z. Lin, Solid State Ionics, 2008, 179, 1697–1701.

[3] H. Ryu, H.J. Ahn, J. Power Sources, 2011, 196, 5186–5190.

[4] I. Bauer, M. Kohl, H. Althues, S. Kaskel, Chem. Comm., 2014, 50, 3208-3210.

Figure 1
Preparation and Stability Research of Ago As Cathode Material
Authors: Yuan Yongqiang
Published: February 2020

Silver-zinc battery (AgO/Zn) is regarded as an energy storage system with advantages of high energy density, high power density and superior rate capability when compared with Ni-MH and lithium battery systems. Due to its relatively high cost, AgO/Zn batteries are widely employed in the field of underwater devices, fish torpedo and aerial/space applications. nanoscaled AgO with high purity was synthesized by a chemical precipitation method, and found this method suited to industrialized production. the electrode offers a discharge voltage plateaus of 1.3-1.58V, a discharge capacity of above 393 mAh·g−1 at 8 C rate ,and an exciting specific power density much higher than the current level for existing secondary batteries and super capacitors.

          As a cathode material for AgO/Zn battery, AgO suffers severely from its poor thermal stability. During long-term storage, AgO decomposes and generates Ag2O and Ag, which in return fasten the decomposition process of AgO. As a result, decomposition issue for AgO even occurs at room temperature. To the best of our knowledge, there is few study regarded to the thermal stability of AgO and no mature fabrication process for AgO has been reported. Na2SiO3, well-know inhibiter, is widely used in alkaline Zn-MnO2 battery to improve stability of the battery. However, there is no systematic investigation of using Na2SiO3 as stability agent in AgO/Zn system. Herein, the effects of Na2SiO3 on the thermal stability and electrochemical performance of AgO are elucidated.

           Through aging treatments, it is concluded that with the introduction of Na2SiO3, the decomposition degree of AgO at room temperature has been reduced to some extent. However, the decomposition temperature of AgO remains unchanged. On the other hand, electrochemical performance of AgO/Zn battery is degraded with addition of Na2SiO3 in the cathode material due to the poor conductivity of Na2SiO3. The results showed that 10 min later after the injection of KOH electrolyte into the cell model, Na2SiO3 mainly influences discharge voltage at early stage when discharging the cell at 4 C with voltage cut-off at 1.0 V. The discharge voltage drop at early stage increases significantly with increasing the amount of Na2SiO3. The open circuit voltage of the AgO with 2wt% Na2SiO3 as cathode was 1.6 V and the voltage suddenly dropped to 1.18 V after the current was applied. The discharge voltage for the AgO with 10.7wt% Na2SiO3 as cathode drastically dropped to 0.2 V under the same test condition. Interestingly, the discharge voltage turned out to be almost identical after discharging for 20 s for all the cells with different weight ratio of AgO as cathodes. These results indicates that the introduction of Na2SiO3 in the AgO cathode mainly influence solution equilibrium.