bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Modeling of the Reaction Mechanism in a Li/O2 Cell: Influence of a Redox-Mediator
Authors: Grübl Daniel , Bergner Benjamin , Janek Jürgen , Bessler Wolfgang G.
Published: February 2020

Interest and research in metal-air batteries is ongoing on a high level due to their high theoretical energy density and potential low-cost materials. Most research activities are performed in the field of lithium-oxygen chemistry with organic electrolytes. This system suffers high overpotentials during charge, indicating asymmetrical charge/discharge reaction mechanisms. High charge overpotentials low the energy efficiency and can increase potential-driven side reactions (e.g., electrolyte decomposition). In order to reduce charge overpotentials, the use of redox mediators has been proposed. Different redox mediators have been demonstrated, such as, TTF [1], LiI [2] and FePc [3]. Bergner et al. introduced 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) as redox mediator [4], which will be further investigated in the present study.

In order to further understand the mechanism of redox mediators, we present a continuum modeling study of a lithium-oxygen cell. The one-dimensional computational domain consists of a gas reservoir filled with oxygen, a porous carbon cathode flooded with an organic electrolyte, a porous separator, and a lithium metal anode. The model includes a detailed description of the electrochemistry in the cathode. During discharge, gaseous oxygen dissolves at the interface between the closed gas reservoir and the cathode (O2,gas ⇄ O2,dissolved). Following, a multi-step mechanism is implemented involving lithium superoxide as intermediate (Li+ + O2 + e– ⇄ LiO2), followed by the formation Li2O2 by chemical disproportion of LiO2 (2LiO2 ⇄ Li2O2 + O2). In the anode the metallic lithium reacts to lithium ions (Li ⇄ Li+ + e–). This mechanism is complemented by charge-transfer of the TEMPO redox mediator (TEMPO ⇄ TEMPO+ + e–), allowing for direct reduction of the lithium peroxide upon charge (Li2O2 + 2 TEMPO+ ⇄ 2 Li+ + O2+ TEMPO). The model is parameterized using experimental data [1]. Galvanostatic discharge and charge simulations reveal the advantage of using a redox-mediator. The electrochemical reaction mechanism and the crystal growth of the sodium superoxide within the cathode is quantified.

Figure
1
: Discharge (left) and charge mechanism involving a redox-mediator (right) in a Li-O2 cathode.

[1] Y. Chen, S. A. Freunberger, Z. Peng, O. Fontaine, P. Bruce, Nature Chemistry 5, 489 (2013).

[2] H.-D. Lim, H. Song, J. Kim, H. Gwon, Y. Bae, K.-Y. Park, J. Hong, H. Kim, T. Kim, Y. H. Kim, X. Lepró, R. Ovalle-Robles, R. H. Baughman, and K. Kang, Angew. Chem. 126, 4007–4012 (2014).

[3] D. Sun, Y. Shen, W. Zhang, L. Yu, Z. Yi, W. Yin, D. Wang, Y. Huang, J. Wang, D. Wang, and J. B. Goodenough, J. Am. Chem. Soc. 136, 8941–8946 (2014).

[4] B. J. Bergner, A. Schürmann, K. Peppler, A. Garsuch, and J. Janek, “TEMPO: A Mobile Catalyst for Rechargeable Li-O2 Batteries,” J. Am. Chem. Soc. 136, 15054–15064 (2014).

Figure 1
Towards Safe Rechargeable K-O2 Batteries
Authors: Wu Yiying
Published: February 2020

Metal-air batteries are promising future energy storage systems. However, they generally have high overpotentials caused by the multi-electron redox processes oxygen goes through in order to store and dispense energy. Therefore, the round-trip energy efficiency is undermined, and the parasitic reactions of electrolyte and carbon electrode cause the decay of capacity and limit the battery life. Here, a K–O2 battery is report that uses K+ ions to capture O2
- to form the thermodynamically stable KO2 product. This allows for the battery to operate through the one-electron redox process of O2/ O2
-. Without the use of catalysts, the battery shows a low discharge/charge potential gap of less than 50 mV at a modest current density. In addition, I will report our recent detailed studies of the side reactions that limit the cycle life of the K–O2 battery, and discuss some methods to address these challenges. I will also address the safety issue considering the use of K metal electrode.
Platinum-Nickel (Pt3Ni) Alloy Nanoparticles Decorated Graphene As a Catalyst of Oxygen Electrode in Li-O2 Cells
Authors: Munichandraiah N , Kumar Surender , Scanlon L G
Published: February 2020

Development of an appropriate bi-functional catalyst for reversible O2 electrode in rechargeable Li-O2 cells is a challenging task. Graphene is an emerging material for several applications owing to its unique properties. In the present study, Pt3Ni alloy nanoparticles anchored onto reduced graphene oxide (RGO) are prepared and investigated as catalyst for Li-O2 cells. For the preparation of Pt3Ni-RGO, commercial graphite powder is oxidized and exfoliated to form graphene oxide (GO). The required quantities of chloroplatinic acid and nickel chloride are dissolved in an aqueous suspension of GO and then reduced by NaBH4 so that the mass ratio of Pt3Ni to RGO is unity.  Pt4+ and Ni2+ ions adsorbed on GO sheets undergo reduction simultaneously with the reduction of GO to form Pt3Ni nanoparticles decorated RGO. The formation and morphology of Pt3Ni-RGO are studied by using powder XRD and TEM. The microscopy image (Fig. 1) indicates the presence of alloy nanoparticles distributed over RGO sheets.

The catalytic activity of Pt3Ni-RGO is investigated  by cyclic voltammetry and rotating disk electrode (RDE) studies in a non-aqueous electrolyte containing tetrabutyl ammonium perchlorate. Cyclic voltammograms recorded at several sweep rates consist of O2 reduction current peaks as well as oxygen evolution current peaks. Both peak currents increase with square root of sweep rate following the Randles Sevcik equation. The RDE studies provide diffusion limited current at several speeds of RDE. The data follow Levich and Koutecky-Levich equations. The values of number of electrons and diffusion coefficient of O2 calculated using these equations are 0.93 and 1.75 x 10-5 cm2 s-1, respectively.

Several Li-O2 cells employing Pt3Ni-RGO as the O2 electrode bi-functional catalyst are assembled and subjected to charge-discharge studies. The discharge capacity obtained at a current density of 0.3 mA cm-2 is 9016 mAh g-1 (8.36 mAh cm-2). It is seen that there is a decrease in discharge capacity initially on repeated charge-discharge cycling. Nevertheless, the discharge capacity stabilizes in a few cycles. The capacity obtained at the end of 10 cycles is 3641 mAh g-1 (3.27 mAh cm-2). Results of these studies will be presented.

Figure 1
Study on the Application of Ailicon-Cobalt Oxide Anode Material in Lithium-Ion Batteries
Authors: Liu Wen-Long , Wang Dong-Xia , Wu Meng-Qiang
Published: February 2020

Silicon (Si)-based materials have the highest capacity among the investigated anode materials and have been recognized as one of the most promising materials for lithium-ion batteries. However, it is still a significant challenge to obtain good performance for practical applications due to the huge volume change during the electrochemical process. To date, the most successful strategy is to introduce other components into Si to form composite or alloy materials.

     In this paper, using the etching technology, porous silicon was prepared, and the silicon and porous silicon were modified by chemical precipitation method. The surface morphology of the obtained material was analyzed by SEM and TEM, the crystalline was characterized by XRD, BET was used to measure the specific surface area and pore size distribution. The charge-discharge properties of the battery, in which lithium as the anode and the prepared materials as the cathode, were analyzed. Then the electrical characteristics were studied by cyclic voltammetry and AC impedance analysis method.

     In the program of charge and discharge experiments of the Li (without modified)/Si battery, the discharge capacity was 2281 mAh g-1 in the first circle, and it will decreased to 555 mAh g-1 in the second circle, indicating the rate of decline up to 75.7%. The results show that the discharge capacitance of the prepared lithium battery using silica, which modified by 12% CoO, as the cathode materials were 3269 mAh g-1 and 2021 mAh g-1 in the first and second circle, respectively, the rate of decline was 38.18%, which is superior than other sample. Using porous silicon modified by variety of weight percentage as cathode materials for lithium batteries, the charge and discharge results showed that when the weight percentage of cobalt oxide fixed at 12% showed the best results, and the first and second discharge capacity was 3590 mAh g-1 and 2679 mAh g-1, respectively, the rate of the discharge capacity decrease was only 25.4%.

      The cyclic voltammetry results showed that the peak current density of Li/Si-CoO (12%) battery was corresponding to the Li/Si system. According to the AC impedance analysis, we inferred the main reason for the decline in silicon battery in the process of continuous charge-discharge is the increase of impedance capacitance of charge transfer (R
ct). The R
ct of the Li/Si battery increased from 9.02 to 13.98 Ω at the end of first and fifth charge and discharge, however, the R
ct of the Li/Si-CoO(12.0%) was 4.52Ω, which is lower than that of the Li/Si battery. The reason may be the volume of expansion and contraction of silicon can be effectively slow down due to the addition of the cobalt oxide. On the other hand, the conductivity may be increased because of the formation of cobalt metal in the process of charge and discharge, which will improve the utilization rate of silicon materials and slow its capacity decline.
Characterisation of Si-Based Anodes for Li-Ion Batteries By Operando Dilatometry and Acoustic Emission Measurements
Authors: Tranchot Alix , Thivel Pierre-Xavier , Idrissi Hassane , Roué Lionel
Published: February 2020

The replacement of graphite by silicon as the active material in negative electrodes of Li-ion batteries is very attractive since the specific capacity of Si is 10 times higher than that of graphite. However, Si suffers from huge volume variation (up to ~300% vs 10% for C) during its lithiation. This leads to the electrode cracking which induces electrical disconnections in addition to cause an instability of the solid electrolyte interface (SEI), resulting in poor cycle life and low coulombic efficiency.

A precise evaluation of the electrode volume variation and cracking upon cycling is thus crucial to develop more efficient Si-based anodes. To date, the study of their morphological changes is usually limited to post mortemexaminations by microscopy. This does not allow a detailed analysis of the morphological degradation process, which can significantly vary depending on the electrode composition and processing, and the charge/discharge conditions.

In the present study, the volume change with cycling of Si-based anodes is monitored by operando dilatometry experiments. For that purpose, a specific displacement transducer is used, which allows measuring expansion or shrinkage of the electrode during cycling down to the sub-micrometer range. Operando acoustic emission (AE) measurements are also performed to study the electrode cracking [1]. The AE technique is based on the detection and analysis of transient elastics waves generated by stress events. The influence of the cycling conditions and electrode formulation on the volume variation and cracking of Si-based electrodes is highlighted, and correlated to their electrochemical performance.

[1] A. Tranchot, A. Etiemble, P-X. Thivel, H. Idrissi, L. Roué In-situ acoustic emission study of Si-based electrodes for Li-ion batteries, J. Power Sources 279 (2015) 259-266.
Mesocellular Carbon Foam (MCF)/Sulfur Composites for High Performance Lithium Sulfur Batteries
Authors: Kim Hyung Sun , Jeong Tae-Kyung , Kim Yong-tae
Published: February 2020

In this study, we introduce a mesoporous carbon  with large pore volume (1.72 cm3/g) and bimodal mesopore structure (4 nm and 30 nm).  Mesocellular carbon foam (MCF) was first synthesized by employing mesocellular silica as a template.  After that, MCF was improved hydrophobicity thorough acid treatment to form stronger bonding between carbon and sodium thiosulfate pentahydrate (sulfur precursor).  MCF/S composite was prepared by solution chemical deposition method (Sol-method).   By Sol-method, sulfur of 73 wt.% was loaded in mesopore channels.  As a result, the composite exhibited enhanced cyclability and retained a stable capacity of 820 mAh/g after 50 cycles.
A Simple Composite Protective Layer Coating That Enhances the Cycling Stability of Lithium Metal Batteries
Authors: Lee Hongkyung , Song Jongchan , Kim Yun-Jung , Noh Hyungjun , Lee Jinhong , Park Jung-Ki , Kim Hee-Tak
Published: February 2020

Metallic lithium is the most promising negative electrode for high-energy rechargeable batteries due to its extremely high specific capacity and its extremely low redox potential. However, the low cycle efficiency and lithium dendrite formation during the charge/discharge processes consistently hinder its practical application. In this report, we present a stabilized Li electrode on which a Li+ ion conductive inorganic/organic composite protective layer (CPL) is coated. With the introduction of the CPL, the Li dendrite growth and electrolyte decomposition are effectively suppressed; consequently, stable Li plating/stripping at high current densities up to 10 mA cm-2 is possible. Nanoindentation tests demonstrate that the shear modulus of the CPL at narrow indentations is 1.8 times higher than that of the Li metal, which provides a theoretical understanding for its efficacy. Moreover, the LiCoO2/Li cell incorporating CPL exhibits excellent cycling stability up to 400 cycles at 1 mA cm-2 (1 C-rate), which demonstrates practical applicability in Li ion batteries through replacing the graphite anode with a CPL-coated Li metal anode.
Polyanion Compounds As Positive Electrode Materials for Rechargeable Aqueous Sodium-Ion Batteries
Authors: Jung Young Hwa , Petla Ramesh Kumar , Kim Joo-Hyung , Lim Chek Hai , Kim Do Kyung
Published: February 2020

Sodium-ion batteries (SIBs) are potential next-generation batteries that can alleviate the cost and resource challenges of lithium. Developing aqueous SIBs is more desirable to emphasize cost-effective factor combining with abundance of Na resources. Aqueous electrolytes exhibit higher ionic mobility as well as are cheaper than organic solvents. Moreover, safety concerns using flammable organic electrolytes could be resolve, therefore aqueous SIB systems would be safer and cheaper than the current organic solvent based LIBs. However, use of aqueous electrolytes imposes a significant challenge in finding appropriate electrode materials that operate within the limited potential window of water while generating reasonably high cell-voltages. Here we introduce two polyanion compounds with carbonaceous composites as promising electrode materials for aqueous SIBs. As the 3-dimensional frameworks of polyanion compounds can accommodate large Na ions and provide easy diffusion path as well as the structural stability, these materials show good cyclability and rate performances especially in safe and environmentally benign aqueous systems. High stability and excellent electrochemical properties of two polyanion compounds, Na2FeP2O7 and Na3V2O2x
(PO4)2F3-2x
, in aqueous electrolytes will be introduced.
A Crosslinked Polyaniline-Coated Graphene Oxide/Sulfur Composite for Lithium-Sulfur Batteries with High Efficiency and Long Cycle Life
Authors: Moon San , Jung Young Hwa , Kim Do Kyung
Published: February 2020

Lithium-sulfur (Li-S) battery has been considered as a promising candidate for future high-energy battery applications due to its high capacity of sulfur (1675 mAh g-1). Li-S batteries, however, have suffered from limited cycle lives, mainly due to the formation of soluble polysulfides, which prevent the practical application of this attractive technology. The encapsulation of sulfur with various conductive materials has addressed this issue to some extent. Nevertheless, most approaches still present partial encapsulation of sulfur and moreover require a large quantity of conductive material (typically, > 30 wt.%), making the use of sulfur less desirable from the viewpoint of capacity. Here, we address these chronic issues of Li-S cells by developing a graphene oxide-sulfur composite with a thin crosslinked polyaniline (PANI) layer. Graphene oxide nanosheets with large surface area, high conductivity and a uniform conductive layer, which are synthesized by a layer-by-layer method, have a synergetic interaction with a large portion of sulfur in the active material. Furthermore, a simple crosslinking process efficiently prevents polysulfide dissolution, resulting in high electrochemical performance, even with a high sulfur content(~75%): high capacity retention of ~80% is observed, in addition to 97.53% of the average Coulombic efficiency being retained after 500 cycles.
The Effect of Lithium Iodide in Li-O2 Batteries
Authors: Lee Seon-Hwa , Kim Hee Min , Hirshberg Daniel , Sharon Daniel , Shin Hyeon-Ji , Aurbach Doron , Sun Yang-Kook
Published: February 2020

Non aqueous Li-O2 battery would seem to be a most promising energy storage and conversion battery system. However, it has practical challenges such as solvent and electrode stability, pronounced overvoltage for oxygen evolution reactions, limited cycle life and poor rate capability. One of the strategies is the use of electrocatalysts. These were used to facilitate oxygen reduction, and the oxidation of the Li2O2 precipitate.1-2 One of the approaches suggested to the fast oxidation of Li2O2 is the use of redox mediators such as iodine. Redox mediators in electrolyte can easily be electrochemically oxidized and transfer electrons to Li2O2.  The latter step considerably reduces the high over-voltage required to oxidize solid Li2O2. One of the redox mediators recently studied in Li-O2 batteries was iodine.3 Iodine and its reduced forms I3- and I- are soluble in polar aprotic solvent. Considering that upon oxidation iodide forms iodine which oxidation, which in turn catalyzes the oxidation of Li-peroxide, the development of Li–oxygen cells with LiI as an additive would look quite promising.4 At very low concentrations of LiI, the iodine formed serves as a redox mediator for Li2O2 oxidation, oxygen is reduced to Li2O2. However, in high concentrations of LiI, the presence of the salt promotes a side reaction that forms LiOH as a major product.

 

 

References

1.          B. D. McCloskey, R. Scheffler, A. Speidel, D. S. Bethune, R. M. Shelby, and A. C. Luntz, J. Am. Chem. Soc., 2011, 133, 18038–18041.`

2.          S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Bardé, and P. G. Bruce, Angew. Chem. Int. Ed. Engl., 2011, 50, 8609–8613.

3.          H.-D. Lim, H. Song, J. Kim, H. Gwon, Y. Bae, K.-Y. Park, J. Hong, H. Kim, T. Kim, Y. H. Kim, X. Lepró, R. Ovalle-Robles, R. H. Baughman, and K. Kang, Angew. Chem. Int. Ed. Engl., 2014, 53, 3926–3931.

4.    S. Meini, N. Tsiouvaras, K. U. Schwenke, M. Piana, H. Beyer, L. Lange, and H. A. Gasteiger, Phys. Chem. Chem. Phys., 2013, 15, 11478–11493.
A Study of Mg Intercalation Mechanism of a Prospective Mg Full Cell Design
Authors: Sa Niya , Burrell Anthony K. , Kinnibrugh Tiffany L. , Wang Hao , Key Baris , Chapman Karena W , Vaughey John T. , Proffit Danielle L. , Chupas Peter J , Fister Timothy
Published: February 2020

A preliminary prospective full cell design composed of V2O5·xH2O as cathode with a Mg metal as anode is constructed where insertion and de-insertion of magnesium into V2O5·xH2O is fully reversible. An in-depth understanding of the Mg intercalation mechanism is investigated by pair distribution function analysis, x-ray absorption near edge structure (XANES) and 25Mg magic angle spinning (MAS NMR) spectroscopy. Interestingly, Mg intercalation results in the formation of multiple phases with different interlayer spacings. Our findings showed that the interlayer spacing of V2O5·xH2O contracts upon Mg intercalation and expands for de-intercalation. An in-depth MAS NMR reveals the existence of two magnesium environments and more interestingly, magnesium intercalation induced a more well-defined Mg-O environment.
Highly Stable and Phenoxide/Alkoxide-Based All Magnesium Electrolytes for Rechargeable Magnesium-Ion Batteries
Authors: Pan Baofei , Burrell Anthony K. , Zhang Zhengcheng , Liao Chen
Published: February 2020

In the last few years, magnesium-ion batteries have received substantial amount of attention for rechargeable energy storage, mainly due to their advantages over traditional lithium-ion batteries in safety, cost and capacity. However, the lack of suitable electrolytes which are capable of depositing magnesium reversibly and efficiently has retarded the progress of magnesium-ion batteries for quite a long time. The current state of art for the design of high potential magnesium electrolytes is focused on the strong Lewis acid derived Grignard reagents or their derivatives. The use of these toxic, corrosive and sometimes combustible strong Lewis acids (aluminum or organoboron-based) brings about safety concern for both the preparation and storage of the electrolytes. As our ongoing effort to implement easily accessible, cost efficient and highly stable electrolytes for magnesium-ion batteries, herein we would like to present our recent progress towards the development of strong Lewis acid-free, highly stable and phenoxide/alkoxide-based magnesium electrolytes. The obtained all magnesium electrolytes possess the oxidative stability up to 3.5 V (vs Mg/Mg2+), which is superior to any strong Lewis acid AlCl3 derived magnesium electrolytes and among the best of all reported magnesium electrolytes capable of depositing magnesium reversibly and efficiently. The excellent reversibility and compatibility in magnesium-ion batteries were further demonstrated using Chevrel phase Mo6S8 as the cathode material, highlighting the great potential of these novel electrolytes for high energy density magnesium-ion batteries. The mechanism behind the chemical reactions has also been extensively investigated by multiple techniques including single crystal X-ray diffraction, NMR and Raman spectroscopies, enabling a comprehensive understanding of the exceptional electrochemical performance of these novel strong Lewis acid-free electrolytes.
Novel Mg Electrolytes for Rechargeable Mg Batteries Based on [Mg2(Î¼-Cl)2]2+ Cation
Authors: Li Guosheng , Cheng Yingwen , Stolley Ryan M , Han Keesung , Shao Yuyan , Liu Jun , Sprenkle Vincent
Published: February 2020

An attractive path to increase energy storage capacities, lower the material costs, and improve operation safety involves the use of multi-valent elements with low reduction potentials. Key benefits of multi-valent systems over mono-valent (i.e. Li, Na) include (1) Increased electrons available per molecule that significantly impacts energy density characteristics. Potential candidates include magnesium (Mg) that can lose two electrons and aluminum three electrons, coupled with increased abundance and decreased production cost makes them viable alternatives for low cost energy storage.  In this presentation, a novel [Mg2(μ-Cl)2]2+ cation complex, which is highly active for reversible Mg electrodeposition, was identified for the first time in this work. This complex was found to present in electrolytes formulated in dimethoxyethane (DME) through dehalodimerization of non-nucleophilic MgCl2 by reacting with either Mg salts (such as Mg(TFSI)2, TFSI= bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl2 or AlCl3).The electrolyte synthesis and understandings developed in this work could be insightful for rational formulation of a family of electrolytes with the general formula [Mg2(μ-Cl)2(DME)4][anion]x, and provide new opportunities for developing cathode materials, and therefore could be significant for practical Mg batteries.
Understanding the Initial Stages of Reversible Mg Deposition and Stripping in Non-Aqueous Electrolytes
Authors: Canepa Pieremanuele , Gautam Gopalakrishnan Sai , Malik Rahul , Rong Ziqin , Zavadil Kevin R , Persson Kristin A , Jayaraman Saivenkataraman , Ceder Gerbrand
Published: February 2020

Rechargeable Mg batteries have been identified as a candidate storage system for the next-generation high energy density rechargeable batteries because of the possibility of pairing a non-dendrite forming Mg metal anode (~2.37 V vs. SHE) with high theoretical specific capacity (2205 A h kg-1) [1] with a Mg intercalation-based cathode. However, several daunting problems still prevent the realization of Mg-battery:  (i) the limited selectivity of electrolyte systems that display reversible Mg deposition, (ii) the narrow electrochemical window of the electrolyte, (iii) lack of high-voltage cathode materials, (iv) irremediable interruption of the battery functions by passivation of the anode material. While it is well established that Mg can be deposited reversibly from complex ethereal solutions of Mg-Chloro complex reagents, the stripping/deposition mechanism at the anode is still debated [2,3]. In this talk we present a detailed atomistic DFT study of the interaction of solvent molecules i.e. THF, and the salts (Mg-Chloro complex) when in contact with Mg-anode surfaces, focusing on the competitive absorption of these chemical species at the interface [4].  Ab initiomolecular dynamics results will complement adsorption calculations providing a better understanding of the morphology of the electrolyte/anode interface. These models are essential to clarify the challenging electron-transfer mechanism occurring at the electrode/solvent interface [4].

References:

[1] D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, and E. Levi, Nature
407, 724–727 (2002).

[2] N. Pour, Y. Gofer, D. T Major, and D. Aurbach, J. Am. Chem. Soc.
133, 6270–6278 (2011).

[3] R. E. Doe, R. Han, J. Hwang, A. J. Gmitter, I. Shterenberg, H. D. Yoo, N. Pour, and D. Aurbach, Chem. Commun.
50, 243–245 (2014).

[4] P. Canepa, G. S. Gautam, R. Malik, S. Jayraman, Z. Rong, K. R. Zavadil, K. Persson, G. Ceder, Chem. Mater. 10.1021/acs.chemmater.5b00389
High Conductive Carbon Nanofiber-Graphite Paper Electrodes with Ultrahigh Polysulfide-Loading for Advanced Lithium-Sulfur Batteries
Authors: Yan Jianhua , Li Bingyun , Liu Xingbo
Published: February 2020

Lithium sulfur (Li-S) battery has attracted much attention due to its high energy density and the abundance of sulfur on the Earth, but some major problems including short cycle life, low sulfur loading, and inferior sulfur utilization have impeded its practical applications. Here, wereport a rational combination of conductive carbon nanofiber-graphite paper (CNGP) with dissolved polysulfides to the formation of advanced sulfur cathode structures that can take full advantage of each building block. The hierarchical CNGP electrode has an ultrahigh sulfur loading of 6.7 mg cm-2, and a high electrical conductivity of 328 S cm-1. In the CNGP electrode, the integrated carbon nanofiber paper (~100 μm) with extremely low density (2.1 mg cm-2) is used as current collector and carrier for the dissolved Li2S6 species, while the densely tapped graphite film (~5 μm) on the top of CNF acts as a protection layer to prevent migration of the dissolved polysulfides from the cathode to the anode. The use of CNGP electrodes and dissolved Li2S6 species enables the fabrication of remarkably improved Li-S batteries with a reversible capacity of 750 mAhg-1 over 300 cycles at 1 C, and 80% of capacity retention from 720 to 580 mAhg-1 over 500 cycles at 1.5 C with an average Coulombic efficiency of 99.5%. The results provide important progress towards the fabrication of Li-S batteries with long cycle life and high rate capabilities.
Carbon Wrapped Sulfur Cathode Materials for Rechargeable Batteries
Authors: Kumar Arun , Gallozzo moises-Miguel , Tomar Maharaj
Published: February 2020

Introduction:

 Currently available rechargeable Li-ion batteries based on spinal, layer and olivine crystal structures of Li (Mn, Ni, Co) Ox and related material systems, shows lower capacity and poor cycling characteristics. In addition, LiCoO2 is expensive and environmentally unfriendly. Due to high volume and gravimetric energy density, rechargeable lithium batteries have become the dominant power source for portable electronic devices including cell phones and laptops. However, the energy and power densities of rechargeable lithium batteries require significant improvement in order to power electric vehicles1. Lower specific capacities of cathode materials (~150mAh/g for layered oxides and ~170mAh/g for LiFePO4) compared to those of the anode (370mAh/g for graphite and 4200mAh/g for Si) have been a limiting factor to the energy density of batteries. It is highly desirable to develop and optimize high capacity cathode materials for rechargeable lithium batteries.

Sulfur is a promising cathode material with a theoretical specific capacity of 1672mAh/g,2 ~ 5 times higher than those of traditional cathode materials based on transition metal oxides or phosphates. Sulfur also possesses other advantages such as low cost and environmental friendly.

Experimental:

Here we present a rational design and synthesis of a novel carbon-sulfur composite material at low temperature. Sulfur particles are synthesized and wrapped by carbon black a simple assembly process. The phase formation behavior of the synthesized powder was investigated using X-ray diffraction, using Cu Kα radiation.  The morphology of the synthesized powder was investigated using a scanning electron microscopy (SEM), and transmission electron microscopy (TEM, Carl Zeiss Leo Omega 922 at 200 KeV).

Result:

The XRD patterns (Fig1.)  of all samples could be indexed to the orthorhombic space group based on the phase –pure ordered structure. Electrochemical properties will be study using cyclic Voltammetry, Charge-Discharge Curves, and Electrochemical Impedance  spectroscopy (EIS). These measurements are still in progress.

Fig1. X ray diffraction patterns of Sulfur-carbon composite (insert morphology image).

References:

Bruce, P. G.; Scrosati, B.; Tarascon, J. Angew. Chem. Int. Ed. 2008, 47, 2930-2946

Ellis, B. L.; Lee, K. T.; Nazar, L. F. Chem. Mater. 2010, 22, 691-714

Figure 1
High Energy Density, Long-Life Li-S Batteries for Aerospace Applications
Authors: Bugga Ratnakumar V , Jones Simon C. , Pasalic Jasmina , Addison Dan , Thiallaiyan Ramanathan
Published: February 2020

Lithium-ion batteries have been successfully employed in several Mars surface missions, e.g., Mars Exploration Rovers (Spirit and Opportunity), Mars Phoenix Lander, and more recently in the Mars Science Laboratory rover (Curiosity).1   With distinct benefits in gravimetric and volumetric densities combined with good low temperature performance relative to the aqueous battery systems, Li-ion batteries contribute to reduced launch costs, increased payload and science capabilities in the space missions.  NASA’s upcoming missions however need energy storage systems with enhanced performance capability, especially higher specific energies and  energy densities.  One such application involves astronaut Extra Vehicular Activity (EVA), wherein the astronaut’s Portable Life Support System (PLSS) is expected to support 8 hours of EVA. The state of art batteries with ~200 Wh/kg at the cell level can support only four hours of EVA. 

            To address these needs, we are developing high-energy and long-life lithium-sulfur cells, with the following performance targets: cell specific energy of 400 Wh/kg ii) cycle life exceeding 200 cycles and iii) ability to operate safely over a wide temperature of -10 to +30 °C.  We have been developing improved cell components for Li-S cells, e.g., protected Li anode, dense sulfur cathode and compatible electrolytes, mainly addressing the key technological hurdlesof poor utilization at high cathode loading (necessary for a practical high energy cell) and limited cycle life.2-5 We have developed new sulfur cathodes that show high specific capacities of ≥800 mAh/g at C/5 rate with practical material loadings, ii) Li anode protected with a polymer electrolyte that displays efficient Li cycling and durability in laboratory Li-S cells, and iii) Electrolytes and new proprietary coatings of polysulfide blocking layers which inhibit the deleterious effects of sulfur redistribution and contribute to a good cycle life.  We have also developed suitable cell designs and fabricated pouch cells that displayed specific energies of ~300 Wh/kg, moderate cycle and safety towards thermal and electrical abuse.  In this paper, we will describe some of these material developments and their performance in laboratory cells and later in prototype cells.

B. V. Ratnakumar,  W. C. West, P. DeGrosse Jr.,  M. C. Smart, L. Jones and R.C. Ewell, NASA Battery Workshop, Huntsville, AL, November 6, (2012)

Y. Yin, S. Xin, Y. Guo and L. Wan, Angew. Chem. Int. Ed. 2013, 52, 13186 (2013).

S. Evers, L. F. Nazar, Acc. Chem. Res., 46, 1135 (2013);

X. Ji, K. T. Lee, L. F. Nazar, Nat. Mater. 8, 500 (2009).

A. Manthiram, S.-H. Chung, C. Zu, Adv. Mater. 27, 1980 (2015).

S. S. Zhang, Front. Energy Res. 1, 1 (2013).
Double Shockley Stacking Fault Formation in Higher Doping Regions of PVT-Grown 4H-SiC Wafers
Authors: Yang Yu , Guo Jianqiu , Goue Ouloide Yannick , Wang H , Wu F , Raghothamachar Balaji , Dudley Michael , Chung G , Quast J , Sanchez E , Manning I , Hansen Darren
Published: February 2020

Due to the influence of facet, the dopant concentration is higher than that other region inside the boule during PVT grown 4H-SiC. A [0001] facet can be observed on top of the boule. The facet region is visible as an oval region of darker contrast indicating a higher doping concentration in c-plane wafers sliced from N-doped 4H-SiC boules. With the help of synchrotron white beam X-ray topography techniques, we have carried out detailed studies on the facet regions in 4H-SiC wafers from different boules. We observed the double Shockley stacking faults piling up insider the facet after the wafer has been subject to chemical mechanical polishing followed by high temperature heat treatment. The partials bonding the stacking faults are along the Peierls valley which is along <11-20> for 4H-SiC. The contrast of double Shockley stacking faults, which are formed by the gliding of two leading partial dislocations on adjacent basal planes, is found only inside the facet region. Our study indicates that the presence of scratch or the other surface source and a higher concentration of N doping within the facet gives rise to the double Shockley faults formation. Moreover, within the facet, the lower minority carrier lifetimes compare to the rest area of the wafer characterized by lifetime mapping measurements also indicates a high density of stacking faults.Due to the facet effect, the dopant concentration is higher than that other region inside the boule during PVT grown 4H-SiC. A [0001] facet can be observed on top of the boule. The facet region is visible as an oval region of darker contrast indicating a higher doping concentration in c-plane wafers sliced from N-doped 4H-SiC boules. With the help of synchrotron white beam X-ray topography techniques, we have carried out detailed studies on the facet regions in 4H-SiC wafers from different boules. We observed the double Shockley stacking faults piling up inside the facet after the wafer has been subject to chemical mechanical polishing followed by the high temperature heat treatment. The partials bonding the stacking faults are lying inside the Peierls valley which is along <11-20> for 4H-SiC. The contrast of double Shockley stacking faults, which are formed by the gliding of two leading partial dislocations on adjacent basal planes, is found only inside the facet region. Our study indicates that the presence of scratch or the other surface source and a higher concentration of N doping within the facet gives rise to the double Shockley faults formation. Moreover, within the facet, the lower minority carrier lifetimes compare to the rest area of the wafer characterized by lifetime mapping measurements also indicates a high density of stacking faults.
(Invited) Vertical GaN p-i-n Diodes Formed by Mg Ion Implantation
Authors: Anderson Travis J , Greenlee Jordan D , Feigelson Boris , Hite Jennifer K , Hobart Karl D , Kub Francis J
Published: February 2020

GaN is an ideal material for power applications due to its high breakdown field, high switching speed, and low switching losses. The ability to implant and activate dopants, particularly p-type dopants, in GaN still remains a challenge. Dopant implantation and activation is crucial for many devices since it is the most straightforward method of selective lateral doping in GaN. Devices such as the current aperture vertical electron transistor (CAVET), Schottky diodes with guard ring termination or grayscale junction termination extension, and vertical p-i-n diodes will be enhanced and enabled by the ability to selectively dope GaN without the need for etching or regrowth. Herein, we report on the first implanted p-i-n diode fabricated on a bulk GaN substrate.

A 8 μm thick unintentionally doped GaN layer was grown by metal organic chemical vapor deposition (MOCVD) on a n+ Ga-face c-oriented GaN substrate. The p-GaN anode and termination regions were formed by Mg implantation to a concentration of 2x1019 cm-3 following a box profile to a depth of 500nm. The implanted dopants were activated using the multicycle rapid thermal annealing (MRTA) technique described elsewhere [1]. After activation and removal of the protective cap structure [2], a 1 μm SiO2 field oxide layer was deposited by plasma enhanced chemical vapor deposition (PECVD). Contact windows were opened by reactive ion etching in a CHF3-based plasma. The anode metal was formed by lift-off of Pd/Au (20/100nm), followed by rapid thermal annealing in a N2atmosphere, and the cathode metal was a blanket film of e-beam deposited Al on the back side of the sample.

Rectifying behavior was observed, a first for a p-i-n structure formed by Mg ion implantation in GaN. The turn-on voltage is consistent with a p-n junction, and the ideality factor of 2.6 is consistent with a recombination/generation-based transport mechanism, confirmed by temperature-dependent I-V. Additional non-ideal behavior is associated with recombination in the drift layer due to crystalline defects. The devices suffer from high ON-resistance due to high contact resistance and recombination in the drift layer, which limited the forward current to 1 A/cm2. Capacitance-voltage measurements indicated the presence of a p-GaN layer, with a depletion layer thickness ~500nm and a doping density of 2x1018 cm-3, corresponding to an activation ratio of 10%.

1. B.N. Feigelson, et. al. J. Cryst. Growth. 350, 21-26 (2012)

2. J.D. Greenlee, et. al. Appl. Phys. Express 8 036501 (2015)
(Invited) Flexible Electronic Skins for Wearable Sensors
Authors: Ko Hyunhyub
Published: February 2020

Flexible electronic skins with high tactile sensitivities have gained great attentions in the fields of wearable sensors, robotic skins, and biomedical diagnostics. Here, we introduce highly-sensitive, multifunctional, and stretchable electronic skins based on interlocked design of micro- and nanostructured hybrid materials. Inspired by the interlocked microstructures found in epidermal-dermal ridges in human skin, piezoresistive interlocked microdome arrays are employed for stress-direction-sensitive, stretchable electronic skins. We show that the interlocked microdome arrays possess highly direction-sensitive sensitive detection capability of various mechanical stimuli including normal, shear, stretching, bending, and twisting forces. We also demonstrate that the bioinspired e-skin design of hierarchical micro- and nanostructured ZnO nanowire (NW) arrays in an interlocked geometry shows a highly-sensitive detection of both static and dynamic tactile stimuli through piezoresistive and piezoelectric transduction modes, respectively. Finally, we show that the stretchable electronic skins attached on the human skin can be used as wearable healthcare monitoring devices, which are able to distinguish various mechanical stimuli applied in different directions, selectively monitor different intensities and directions of air flows and vibrations, and sensitively monitor human breathing flows and voice vibrations.
(Invited) Probing Metal-Graphene Interactions with Raman Spectroscopy
Authors: Cheng Guangjun , Calizo Irene , Hight Walker Angela R.
Published: February 2020

Metal-graphene interactions play important roles in the fields of catalysis and electronics. In this talk, we demonstrate that Raman spectroscopy is a powerful tool to probe these interactions and will present two specific cases. First, we investigate the Fe-catalyzed etching of graphene layers in forming gas. Fe thin films are deposited by sputtering onto mechanically exfoliated graphene, few-layer graphene (FLG), and graphite flakes on a Si/SiO2 substrate. When the sample is rapidly annealed in forming gas, particles are produced due to the dewetting of the Fe thin film and those particles catalyze the etching of graphene layers. The microscopic and Raman spectroscopic evidence reveals that monolayer and FLG regions are severely damaged and that the particles catalytically etch channels in graphite. No etching is observed on graphite for the Fe thin film annealed in nitrogen. The critical role of hydrogen indicates that this graphite etching process is catalyzed by Fe particles through the carbon hydrogenation reaction. By comparing with the etched monolayer and FLG observed for the Fe film annealed in nitrogen, our Raman spectroscopy measurements identify that, in forming gas, the catalytic etching of monolayer and FLG is through carbon hydrogenation. During carbon hydrogenation, Fe particles are catalytically active in the dissociation of hydrogen into hydrogen atoms and in the production of hydrogenated amorphous carbon through hydrogen spillover. In the second case, we deposit a Ni thin film by thermal evaporation onto mechanically exfoliated graphene, FLG, and graphite, and probe the Ni-graphene interface using Raman spectroscopy. When the sample is annealed in forming gas, a Ni(111) thin film is produced on graphene, FLG, and graphite. We observe the disappearance of Raman signals from graphene underneath Ni(111) when using  low laser power and the re-appearance of the Raman signals from the graphene with a higher power excitation laser. This work provides direct experimental evidence for the strong interaction between Ni(111) and graphene and confirms the result from the theoretical simulations that this strong interaction suppresses the Kohn anomaly in graphene.
(Invited) Electrochemical Nanowire Devices for Energy Storage
Authors: Mai Liqiang , Zhou Liang , Tian Xiaocong , Sun Ruimin , Yan Mengyu
Published: February 2020

Nanowires have attracted increasing interests due to the one-dimensional nanomaterials can offer a range of unique advantages in many energy related fields. For previous lithium battery application, bulk materials made of nanowires were usually used as the electrodes. Although the electrochemical properties could be improved, the fast capacity fading is still one of the key issues and the intrinsic reasons are not clear until now. To understand intrinsic reason of capacity fading, we designed the single nanowire electrochemical devices for in situ probing the direct relationship between electrical transport, structure, and electrochemical properties of the single nanowire electrode. Our results show that conductivity of the nanowire electrode decreased during the electrochemical reaction, which limits the cycle life of the devices. Based on this conclusion, a series of hierarchical structures nanowires have been obtained, including hierarchical MnMoO4/CoMoO4 heterostructured nanowires and hierarchical mesoporous La0.5Sr0.5CoO2.91 nanowires which show enhanced performance in Li-air batteries and supercapacitors.1 In our present work, a series of novel nanowire architecture have been designed and synthesized, including kinked hierarchical nanowires, hierarchical heterostructured nanowires and hierarchical scrolled nanowires which shows great electrochemical and biological probe performances.2-4 It is expected that our research may extend effective and helpful methods in directions that will solve the challenge of property degradation in energy storage and open new applications.5

References

[1] L. Mai, et al., Nat. Commun., 2011, 2: 381.

[2] L. Mai, et al., Nat. Commun., 2013, 4: 2923.

[3] Q. Qing, et al., Nat. Nanotechnol., 2014, 9, 142.

[4] Y. Zhao, et al., Nat. Commun., 2014, 2014, 5: 4565

[5] L. Mai, et al., Chem. Rev., 2014, 114, 11828.
Simulation of the pH Sensing Capability of an Open-Gate GaN-Based Transistor
Authors: Patrick Erin , Choudhury Mohua , Law Mark E
Published: February 2020

Heterostructure transistors based on the AlGaN/GaN material structure are popular for chemical and biological sensors because of their nontoxicity and chemical inertness in biological or corrosive environments.  They also offer very high sensitivity as a result of the very large gain and transconductance. Studies over the years show much research on this technology for sensing applications including pH sensing, prostate cancer detection, and breast cancer detection. However, the designs of these devices are not optimized because of nonexistent or rudimentary modeling and simulation support.

Commercial software packages adept at simulating III-V-based transistors do not have applications built-in for chemical sensing capability. Current research relies on analytical models and in-house numerical programs to do specific and limited simulations.

We build upon a TCAD simulation framework (FLOODS) specifically suited for III-V device simulation that is capable of self-consistent, fully-coupled simulation of reaction-dependent physics at the electrolyte/semiconductor interface.  This paper outlines the simulation methodology for a pH sensor using an open-gate AlGaN/GaN High Electron Mobility Transistor (HEMT).  The interfacial reactions are coupled to traditional device simulation equations, i.e. Poisson and carrier continuity.  This enables surface charging reactions to be directly coupled to the device output terminal characteristics. We also solve for electrostatic field and ion transport in the electrolyte. This work will enable optimization of specific sensor technologies or exploration of the fundamental physics behind the sensing mechanism.
Investigation of the Dynamic Relaxation Behavior of Biomolecules Immobilized on Metal Electrode in Time Domain
Authors: Hsu Chen-Pin , Wang Yu-Lin
Published: February 2020

Biomolecules such as DNA immobilized on metal electrodes and non-Faradaic current was measured in buffered solution. The metal-biomolecules-liquid-metal structure can be regarded as a liquid type of capacitor. The measurement of the capacitive current, which is affected by the ions, biomolecules, and liquid in the solutions. It is interesting to investigate the charging and discharging process in time domain, which brings important information of the dynamic behavior of the whole system. In this study, double-stranded DNA (dsDNA) was immobilized on gold electrodes and the capacitive current was measured in buffer solution with a pulse stimulus. Different relation time constants were revealed for various surface modifications. The transient current of the sensor was measured in de-ionized water and in 30 mM TE buffer before dsDNA immobilized metal electrode, and in 30 mM TE buffer after dsDNA immobilized on the metal electrode, followed by different concentrations of HIV-1 RT protein, ranging from 1 aM to 100fM. This technique shows ultra-high sensitivity of the protein detection (1 aM), indicating that this technique is promising for biosensor applications.

 Figure 1 shows the schematic of device for capacitive current measurements.