bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Reactions in Li-Ion Battery Electrodes and Their Interaction with Mechanical Stresses: Size Effects, Phase Segregation, and Crack Propagation
Authors: Stein Peter , Zhao Ying , Xu Bai-Xiang 
Published: February 2020

Since their introduction 25 years ago, lithium-ion batteries have risen to become the primary power source for mobile devices such as electric tooth brushes and razors, but also for cellphones and tablet PCs. They have a high potential for wider application, e.g. in (hybrid) electric vehicles or for the storage of renewable energy. This is currently hindered by the gradual capacity fade over cycle lifetime. Main factors for this degradation are electrochemical side-effects such as SEI formation and mechanical damage. The cyclic insertion and extraction of Li ions results in high stress levels in and large deformation of the electrodes, leading to delamination of the electrode structure and to fracture of individual particles, respectively. The freshly cracked surface is then exposed to further chemical reactions. Experimental evidence however suggests, that nanostructured electrodes exhibit a higher resilience against this diffusion-induced mechanical degradation.
In this talk, we report on our efforts towards modeling the chemo-mechanical processes taking place in free-standing electrode particles at the micro- and the nano-scale. In particular, we describe two models used to study the interaction of phase segregation and crack growth, as well as the interaction of chemical reactions and surface tension in nanoparticles. Both models feature a direct coupling between diffusion and elasticity as well as concentration-dependent diffusivity. In particular, the Butler-Volmer relation for the description of electrochemical surface reactions has been modified to account for the effects of mechanical stress and phase formation.
We show that surface tension provides mechanical stabilization in nanoparticles, allowing, in principle, for higher charge/discharge rates. This effect is size-and shape-dependent. Due to surface tension, however, the usable capacity of a particle shrinks with its size. Regarding phase segregation, we demonstrate how the rate of surface reactions can determine the separation behavior, and that the evolution of the phase interface can drive the propagation of pre-existing cracks in an electrode particle.
A Study of Mediators As Ion Providers in Supercapactors
Authors: Zhou Xiangyang , Zhang Chen , Wang Yuchen , Qiao Xiaoyao 
Published: February 2020

Doping mediators (soluble redox compounds) in polymer electrolyte contained in the porous electrodes is an effective method to increase the capacitance of supercapacitors. Mediators not only provide additional capacitance but also ions to electrolyte. The total capacity of a supercapacitor is dominated by the minor of the electrode capacity and the number of ions in electrolyte. In this research, we focused on revealing the effect of on the extra ions provided by the mediators during the charge/discharge processes. Two types of supercapacitors were fabricated. For the first type, the active electrode material consisted of 50 wt% mediators (in solid state) and 50 wt% high specific surface area active carbon (AC). For the other type of supercapacitor, the active electrode material consisted of AC only. Acetonitrile was used as liquid phase for both types. Under this circumstance, ions are provided by mediator only. The calculation of specific current was based on total weight of two electrodes and cyclic voltammetry (CV) curves. As shown in Figure 1, supercapacitor (a) (AC only) is unable to store any charges and energy without the ions in the solution. However, supercapacitor (b) can store ten times more energy with the mediator enhancement. In this situation, we can consider mediators as ‘charge harbor’. They can release ions into the liquid phase. These ions then participate in formation of electric double layers (EDLs) on AC. This capability of providing ions into the liquid phase can increase capacity of supercapacitor. CVs (b) and (c) also indicate that different mediators are different in the kinetics of providing ions. Taking supercapacitor (b) as an example, when we charge the supercapacitor, the K2CuFe(CN)6
can release K+ cation into the liquid phase and [CuFe(CN)6]- will still be hold on the solid phase because of the electrostatic force. On the other hand, we can use VOSO4 as a mediator too. V4+ can be reduced and releases SO4
2- anion. Thus, it is preferred to use K2CuFe(CN)6
in the positive electrode while use VOSO4 in the negative electrode. An series of mediators were evaluated using the same method.

Figure 1
How to Enhance the Performance of Graphene/Metal Oxide Nanocomposite Supercapacitors
Authors: Shim Jae-Jin , Nguyen Van Hoa , Sahoo Sumanta , Mohamed Saad Gomaa , Hwang Jinho 
Published: February 2020

Graphene/metal oxide nanocomposites have been developed for energy storage applications such as supercapacitors, catalysts, sensors, and batteries. Electrochemical performance of the nanocomposites has been improved so much due to the synergistic effect of excellent conductivities and mechanical properties of graphene sheets and the high pseudocapacitance of metal oxides. For the applications of these nanocomposites to the real supercapacitors, a huge enhancement in capacitance, cycling stability, energy density, and power density should be achieved, resulting in an excellent performance as an electrode material for supercapacitors.
In this study, we have tested several methods to enhance the supercapacitor performance, such as doping of graphene with other elements and using mixed metal oxides and conducting polymers. We have achieved high surface area, high conductivity, and remarkable electrochemical properties (specific capacitance of over 4,000 F/g). Cleaner synthetic methods have also been involved in the synthesis process.
Local Variation in Microstructure Causes Heterogeneity in the Conductivity of Commercial Lithium-Ion Cathode Films
Authors: Vogel John E , Clement Derek V , Hardy Emilee , Mazzeo Brian A , Wheeler Dean R 
Published: February 2020

The electrical conductivity of battery films is an important characteristic in how battery cells perform but is not very well understood on a µm scale. Although the macroscopic electrical conductivity of battery films has been explored, small-scale variations in the film have been shown to exist [1]. Factors that may affect this heterogeneity include film composition as well as manufacturing steps such as drying and calendering [2].
We show that in commercial quality battery electrode films there is not only expected variation on a micrometer scale, but that measured conductivity variation can occur on the order of millimeters. A modified micro-N-line probe [1] was installed in a high-resolution stage for taking local measurements of conductivity. Electrical conductivity of battery films was then mapped.
A key advance in this work is the correlation of local conductivities with the local microstructure. ”Hot”, ”average” and ”cold” conductivity spots were investigated by scanning electron microscopy (SEM) with focused ion beam (FIB) milling in order to produce planar cross sections. The SEM/FIB images were then segmented into 3 major domains: carbon-binder, active material, and large pores. We see a strong correlation between conductivity and both porosity and carbon volume fraction, consistent with macroscopic trends observed in our previous research [3].

Acknowledgements

This research is supported by the US Department of Energy through the Advanced Battery Material Research (BMR) Program.

References

[1] B. J. Lanterman, A. A. Riet, N. S. Gates, J. D. Flygare, A. D. Cutler, J. E. Vogel, D. R. Wheeler, and B. A. Mazzeo, “Micro-four-line probe to measure electronic conductivity and contact resistance of thin-film battery electrodes,” Journal of the ELectrochemical Society, vol. 162, no. 10, A2145–A2151, 2015.
[2] M. M. Forouzan, C.-W. Chao, D. Bustamante, B. A. Mazzeo, and D. R. Wheeler, “Experiment and simulation of the fabrication process of lithiumion battery cathodes for determining microstructure and mechanical properties,” Journal of Power Sources, vol. 312, pp. 172–183, 2016.
[3] S. W. Peterson and D. R. Wheeler, “Direct measurements of effective electronic transport in porous li-ion electrodes,” Journal of the Electrochemical Society, vol. 161, no. 14, A2175 –A2181, 2014.

Figure 1: (a) Shows a local map of resistivity taken on an NMC TODA 523 cathode with locations A, B, and C marked where further investigation was carried out. (b) Shows FIB/SEM investigation of point B. (c) Shows segmentation of the FIB/SEM image into 3 domains: carbon-binder (grey), active material (white), and large pores (black). (d) Shows volume fractions taken over a large range of samples for high-conductivity, average-conductivity and low-conductivity locations.

Figure 1
Crystalline Porous Materials and Their Applications in Electrochemical Energy Storage Devices: Lithium Batteries and Li-Sulfur Batteries
Authors: Zhang Zhongyue , Awaga Kunio , Wu Yang 
Published: February 2020

The development of new electrochemically active materials towards the application of battery electrodes is still one of the most intriguing topics in energy-related science. A good electrode material requires not only a large energy storage density, but also high permeability to electrolytes and robustness during the electrochemical process. From the perspective of synthetic material science, we chose highly crystalline porous materials, including metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) as the target of research. The crystallinity of materials guaranteed the stability upon the electrochemcial treatment, while the porosity allowed the penetration of electrolytes and a high mobility of ions in the materials. Towards Li-ion batteries, we could achieve the electron accepting ability on both metal cation clusters and organic linkers of MOFs with proper design strategies and a total capacity that is comparable with major commercialized batteries has been obtained. A series of physical measurements were performed and resulted an insight to the mechanism of the electrochemical processes, hence the discovery of a "bipolar charging" mechanism that has not been observed for traditional Li-ion batteries. Such mechanism utilized the insertion of both Li-ions and anions from the electrolyte, which alternates the doping feature and the ionic conductivity of MOFs in electrochemical steps. We also examined the potential of these porous materials as the substrate of sulfur in the cathode of Li-S batteries, as they can easily separate sulfur into nanoparticles through a simple adsorption approach. We performed studies on a series of isoreticular MOFs, UiO-66-68, which adopt same structural topology and the only difference is pore size and pore volume. The C-rate dependent electrochemcial behavior of sulfur impregnated MOFs were analyzed and suggested the importance of pore size. Furthermore, we prepared MOFs and COFs with functionalized sulfur binding groups, and the linkage between the sulfur and porous frameworks generated a new type of polymer, namely MOF/COF-graft-polysulfides. These new type of polymers were applied as the cathode materials of Li-S batteries, and the binding groups sucessfully increased the cyclic performance of Li-S batteries referencing with non-functionalized MOFs/COFs.
In-Operando Investigation of Rechargeable Aqueous Sulfate Zn/MnO2 Batteries
Authors: Chamoun Mylad , Brant William Robert , Karlsson Gunder , Noréus Dag 
Published: February 2020

Large-scale energy storage necessitates inexpensive, safe and long life batteries. Present battery development is rapid but based on insufficient materials for large scale power grid applications. The Zn/MnO2 battery has high energy density comparable to Li-ion batteries and delivers a lower price per kilowatt-hour. Nonetheless, the rechargeability of the battery is limited and the cathode suffers from an irreversible phase formed during cycling. In the traditional alkaline battery, the irreversibility arises from a spinel phase that is electrochemically inactive. In this work, we use a zinc sulfate electrolyte and thus the reaction mechanisms are different. The inactive phase corresponds to a basic zinc sulfate precipitate passivating the electrode surface. Noteworthy suppression of the inactive precipitate can be achieved by adding small amount of manganese sulfate into the electrolyte. Our current Zn/MnO2 cells have achieved stable capacity retention over 100 cycles by using commercially available materials. Specific capacity of 230 mAh/g and coulombic efficiency around 99.9% of the MnO2 electrode as well as a mid-point voltage of 1.35 V was achieved.
We describe the phase transformations and the failure mechanisms of the cathode in the aqueous zinc sulfate Zn/MnO2 battery, with and without the manganese sulfate. The phase transformations occurring in the cathode are directly observed with in-house in-operando X-ray diffraction using a Mo-source and 2D detector for rapid data acquisition. The manganese dioxide electrode is reversible over several charge and discharge cycles. The basic zinc sulfate dissolves and precipitates facilely if manganese sulfate is added. We discuss the factors of this reversibility in perspective of pH and surface area. Furthermore, we describe the structural changes and the electrochemical performance of the cathode using X-ray radiation, analytical and electrochemical techniques.
Our results can make it possible to further improve this battery to make it a worthy contender to the Li-ion battery in large-scale storage applications.
Figure (left): Charge and discharge curves of Zn/MnO2 cell at C/5. Figure (right): Specific discharge capacity and efficiency vs. cycle number of two Zn/MnO2 cells over 100 cycles.

Figure 1
Electro-Oxidation of Borohydride in a Molten Alkali Hydroxide Eutectic Mixture and a Novel Borohydride/Periodate Molten Electrolyte Battery
Authors: Gyenge Elod L. , Wang Andrew 
Published: February 2020

The NaBH4 electro-oxidation kinetics in a molten NaOH-KOH eutectic mixture (0.585:0.415 mole fractions) is investigated on Ni, electrochemically oxidized Ni and Pt electrodes in conjunction with the performance of a novel NaBH4/KIO4 battery [1, 2]. The oxidized Ni shows excellent electrocatalytic activity towards BH4
- oxidation at 458 K, with apparent exchange current density, Tafel slope and electron transfer coefficient of 22.54 mA cm-2, 127 mV dec-1 and 0.7 respectively. The activation energy of the BH4
- oxidation reaction is 16.3 kJ mol-1. The BH4
- diffusion coefficient was determined using a chronoamperometric technique. X-ray photoelectron spectroscopy (XPS) analysis of the anodically oxidized Ni reveals the formation of NiO, which is responsible for the increased catalytic activity towards BH4
- oxidation compared to the untreated Ni electrode. A compact molten NaOH-KOH eutectic electrolyte battery with dissolved NaBH4 at the anode, immobilized KIO4 at the cathode and sintered Ni separator, was assembled and investigated for the first time. An oxidized Ni gauze served as the anode, whereas the cathode was Pt mesh containing the immobilized KIO4. Figure 1 a and b, show the NaBH4/KIO4 battery polarization curves as a function of NaBH4 molal concentration and the discharge cell voltage profile over time at 160 mA cm-2, respectively.

Fig. 1: a) Polarization curves of the NaBH4/KIO4 battery at 458 K in the NaOH-KOH eutectic mixture, b) Constant current discharge at 160 mA cm-2 with 500 milimolal NaBH4. Oxidized Ni gauze anode; Pt gauze cathode with 2.5 g cm-2 loading of KIO4; electrolyte: NaOH-KOH eutectic mixture with mole fractions 0.515:0.485.
Factorial design of experiments revealed the main and interaction effects influencing the power output of the NaBH4/KIO4 battery. Temperature and cathodic KIO4 loading have the most significant main effects on the power density, whereas the NaBH4 concentration in the molal concentration range of 50 to 500 milimolal, has a comparatively smaller effect. A maximum power density of 210 mW cm-2 is achieved at 458 K. With further research and development it is proposed that the NaBH4 – KIO4 battery could be used together with solar – thermal energy storage systems.
References:

A.Wang and E.L. Gyenge J.Power Sources 282 (2015) 169-173.

A. Wang and E.L. Gyenge, manuscript in preparation (2016).

Figure 1
Cycling Life Prediction By Reaction Depth Index Analysis of Lead Acid Battery
Authors: Dai Changsong , Yang Shaoqiang , Li Ruhong , Cai Xianyu , Xue Kuiwang , Yang Baofeng , Hu Xinguo 
Published: February 2020

The use of energy storage lead acid batteries in deeper discharge leads to a pronounced capacity fading and too short life. Now the analysis of positive active material (PAM) composition was the average content of plates. So exploring the influence of positive additives to PAM and cycle life in lead acid batteries was very limited. In addition, the cycle life test of lead acid batteries, especially at relatively high depth of discharge (DoD) could continue for months, even years. It’s always a challenge to the efficiency of research and development of new products. In our work, plates with different DoD have been divided into five layers from surface to center of section. The content of PbO2 in above samples have been characterized by X-ray diffraction (XRD). The reaction depth index of Plates has been obtained by Gaussian fitting of PbO2 content distribution curves of section direction. Addition of metallic sulfate and metallic oxide into the active mass of positive electrode clearly extended the cycle life of batteries. Through contrastive analysis of different lead acid batteries, it has been established that lower reaction depth index was beneficial for the cycle life of batteries. Upon the relationship between reaction depth index and cycle life of lead acid batteries, the cycle life of new battery could be predicted accurately.
Fig.1 the relationship of DoD, reaction depth index and cycle number

Figure 1
(Invited) Fullerene Cation-Mediated Demethylation/Cyclization to 5- and 7-Membered Cyclo[60]Fullerene Derivatives
Authors: Matsuo Yutaka , Ogumi Keisuke , Okada Hiroshi , Nakagawa Takafumi 
Published: February 2020

This presentation reports on new cyclization reaction by using fullerene cation to obtain 5- and 7-membered cyclo[60]fullerene derivatives. In this talk, mainly we focused on development of methodology to obtain new fullerene derivatives utilizing cationic fullerene intermediate, and discussed reaction mechanism involving fullerene cation which can be coordinated by benzene rings or the oxygen atom, affording migration of the phenyl groups and activation of the methyl group of the methoxy group for demethylative cyclization.[1]

Single-bonded fullerene dimers, (C60R)2 (R = (2-methoxyphenyl)dimethylsilylmethyl, (isopropoxy)dimethylsilylmethyl, and 2-methoxy-5-methylphenyl), afforded fullerene derivative cations (RC60
+) in the presence of an oxidant (I2, CuCl2, or CuBr2), leading to 5- and 7-membered cyclo[60]fullerene derivatives such as cyclo[60]fullerenes containing a Si–O bond, cyclo[60]fullerenes containing a C60–O bond, and dihydrobenzofurano[60]fullerene. The reaction mechanism involved thermal homolytic cleavage to give fullerene radical, oxidation of the radical to generate fullerene cation, and then demethylative cyclization in which the fullerene cationic centers interact with an aromatic group or the oxygen atoms of methoxy groups to produce the cyclized products. Obtained cyclo[60]fullerene derivatives were used in bulk-heterojunctoin organic solar cells and showed moderate power conversion efficiency and respectable open-circuit voltage.
[1] Y. Matsuo, K. Ogumi, Y. Zhang, H. Okada, T. Nakagawa, H. Ueno, A. Gocho, E. Nakamura, J. Mater. Chem. A, in press.

Figure 1
(Invited) Liquid-Exfoliated Transition Metal Dichalcogenides: A Story of Excitons, Spectroscopic Metrics and Functionalisation
Authors: Backes Claudia , Rashvand Farnia , Synnatschke Kevin , Knirsch Kathrin , Cieslik Patrick , Lafargue Paul 
Published: February 2020

Liquid exfoliation has become an important production technique to give access to large quantities of two-dimensional nanosheets in colloidal dispersion.[1] Importantly, this is a highly versatile technique that can be applied to numerous layered materials beyond graphene such as transition metal dichalcogenides, III-VI semiconductors, black phosphorus, layered oxides to name just a few. These can be cast into films and composites and have proven useful in a number of application areas. However, as produced dispersions contain a nanosheets of various sizes and thicknesses making post-exfoliation size selection extremely important to tap the full potential in the future. We have previously developed a universal and efficient size selection technique termed liquid cascade centrifugation.[2] Optimisation of this centrifugation procedure allowed us to produce monolayer-rich dispersions with monolayer volume fractions up to 75%. This was made possible because we have realised that nanosheet size and thickness, as well as monolayer content can be quantitatively extracted from for example optical extinction spectra due to edge and confinement effects greatly facilitating and accelerating the characterisation.[2,3]
We now use this basic understanding and these improvements in sample quality to systematically investigate the effect of the chemical environment on the optical properties of the liquid-exfoliated nanosheets. For example, we show that the A-exciton energy depends on the layer number in a similar way for a number of different TMDs. Furthermore, dielectric screening from additives and solvents can be tracked via this A-exciton layer number dependence making this an ideal fingerprint for noncovalent functionalisation.[4] Last but not least, we show that the ability to dramatically increase the surface area of the layered materials on exfoliation can be used to explore new chemistry and to controllably functionalise either basal plane [5,6] or edge sites.

[1] Bonaccorso, F., Bartolotta, A.; Coleman, J.N., Backes, C., Adv. Mater.
2016, 28, 6136-6166.
[2] Backes, C.; Szydłowska, B.M.; … Coleman, J. N.,
ACS Nano
2016, 10, 1589-1601.

[3] Backes, C.; Smith, R. J.; … Coleman, J. N., Nature Communications
2014,
5, 4576.
[4] Vega-Mayoral, V.; Backes, C.; …. Coleman, J. N., Adv. Func. Mater.
2016, 7, 1028-1039.
[5] Backes, C.; Berner, N. C.; …. McDonald, A., Angew. Ch. Int. Ed..
2015, 54, 1-6.
[6] Knirsch, K.; Berner, N. C.; …. Backes, C., ACS Nano
2015, 9, 6018-6030.