bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation Between Microstructure Parameters and Performance Characteristics of Lithium-Ion Cathodes
Authors: Costard Janina , Raumer Michael , IJsselstein Tim , Gerthsen Dagmar , Ivers-Tiffée Ellen 
Published: February 2020

Lithium-Ion Batteries receive growing attention because of their potentially high energy and power density, which are important requirements for automobile applications. Reports agreed that the positive electrode is hereby the performance limiting cell component.
NxMyCz (nickel manganese cobalt spinel) is one of the most promising cathode materials, both due to its rather high operating voltage and to either high power or energy density [1]. Hereby, a compromise between high power (thin layers and, i.e., high porosity) and high energy density (thick layers and, i.e., low porosity) has to be reached, in particular for automotive applications. This demands for an extended understanding of the interplay between microstructure parameters and chemical stoichiometry of NMC cathodes on cell performance characteristics.
In this study, two NMC - cathodes recovered from commercial high energy and high power cells are analyzed (i) by SEM and X-ray tomography and (ii) by Electrochemical Impedance spectroscopy (EIS). By evaluating the impedance spectra measured at 0 to 40°C and at SOC 0 to SOC 100 by the distribution function of relaxation times (DRT) [2], a physically motivated transition line model [3] was established. The microstructure parameters required for a quantitative analysis of the electrochemical loss processes were obtained by X-ray tomography data. Additionally, the exact composition is determined by energy dispersive X-ray spectroscopy (EDX) investigations
The results confirm, that a NMC electrode custom tailored for high energy density is rather thick (70 µm) and made of large low-porous agglomerates of primary particles, as described in [4]. The significant difference between the NMC cathode of a high energy and a high power cell however is not, as expected, a significantly higher porosity, but a sophisticated combination of small carbon black particles and elongated carbon black fibers, enabling high discharge currents. The tortuosity of the electrode pores, which represent the transport pathways for the liquid electrolyte, is low for the high power cell, which raises the effective electrolyte conductivity significantly, when compared to the high energy cell [4]. Furthermore the high power cell features a special compound of two different NxMyCz active materials. By including all the results from EIS, DRT, X-ray tomography and EDX, an evaluation of the influence of composition and microstructure on performance characteristics of the NxMyCz cathodes will be presented.

References

[1] K.C. Kam, A. Mehta, J.T. Heron, M.M. Doeff, Journal of the Electrochemical Society 159 (2012) A1383–A1392.
[2] J. Illig, Physically based Impedance Modelling of Lithium-Ion Cells (2014)
[3] J. Euler, W. Nonnenmacher, Electrochimica Acta 2 (1960) 268–286.
[4] M. Ender, J. Joos, A. Weber, E. Ivers-Tiffée, Journal of Power Sources 269 (2014) 912–919.
Identification of Failure Mechanisms in Si Electrodes for Li-Ion Batteries
Authors: Beattie Shane D , Loveridge Melanie 
Published: February 2020

Introduction:

Silicon anodes are studied as a high capacity alternative to graphite for Lithium-ion batteries. Unfortunately, when silicon anodes are paired with commercially relevant cathodes the cell suffers from rapid capacity fade. Failure mechanisms resulting in rapid capacity fade are identified using three techniques: i) study of voltage-capacity profiles from three-electrode cells, ii) the effect of upper cut-off voltage on capacity retention, and iii) ex-situ X-ray diffraction.

Discussion:

Most commercial Li-ion cells are cycled using a constant-current, constant-voltage profile. Voltage limits are typically set between 3 and 4.2 V. When using novel cell chemistries it is important to understand how industry standard cycling profiles affect the evolution of the voltage–capacity profile. Anode/cathode voltage is tracked in a three electrode cell to understand how the voltage profile of each electrode evolves over time/cycle number. Data shows that as silicon electrodes are cycled they lose capacity/active lithium inventory (Figure 1). Silicon electrodes have a sloping voltage profile. When lithium inventory is depleted the end of charge voltage at the anode will increase; correspondingly, the end of charge voltage at the cathode will increase (> 4.4 V vs. Li). This rise in voltage at the end of charge will liberate more lithium from the cathode, replenishing some of the lost lithium inventory. This has short term gains by replenishing the lost lithium inventory, but long term consequences as cathodes do not cycle well at higher voltages (Figure 2).
Ex-situ XRD data shows that when silicon electrodes are cycled to less than their theoretical capacity, the conversion from crystalline to amorphous silicon is continuous (Figure 3). This suggests that previously amorphized silicon is not preferentially lithiatied, contrary to voltage considerations. The data suggests that crystalline particles continue to crack during cycling, exposing fresh crystalline silicon surfaces. Lithium reacts at the newly formed crystalline silicon surface due to its close proximity to the electrolyte, rather than diffusing through the bulk to reach previously amorphized Si. This process results in continued decomposition of electrolyte, and formation of excessive SEI. XRD and electrochemical data show that the conversion from crystalline to amorphous silicon stops above ~ 180 mV.

Conclusion:

Results from three-electrode cells clearly show an increase in end of charge voltage at the anode/cathode as a function of time/cycle number. The end of charge voltage at the cathode reaches above 4.4 V, which is beyond the recommended cycling regime of the cathode and electrolyte. This rise in end of charge voltage results in decreased cycling efficiency and rapid loss of capacity. XRD data shows that when Si electrodes are cycled to less than their theoretical capacity the conversion of crystalline Si to amorphous Si is continuous below a voltage of ~ 180 mV.

Figure 1
Characterization of Structure and Electronic States of La0.5Ca0.25MnO3 surface By First-Principles Simulation
Authors: Ando Yasunobu , Nakamura Sunya , Minamitani Emi , Shimizu Ryota , Iwaya Katsuya , Ohsawa Takeo , Hitosugi Taro , Watanabe Satoshi 
Published: February 2020

Perovskite oxides (perovskites) are promising candidates for oxidation catalysis in solid-state fuel cells because of their high chemical activity on the surface and variety in composition. However, direct observation of their surface structures and properties has been difficult due to the lack of easy-cleavage plane. Research on the clean surfaces of perovskites has been demanded.
Recently, some of the coauthors of this presentation have succeeded in epitaxial growth of La0.75Ca0.25MnO3 (LCMO) thin films and their scanning tunneling microscope (STM) obsearvation at low temperature (see Fig. 1). They found that the LCMO surface is reconstructed and shows a zigzag pattern with √2×√2 periodicity. They also revealed via scanning tunneling spectroscopy that the surface is insulating. In order to identify its atomic structure and mechanism of its insulating nature, we have carried out first-principle simulations with the LCMO slab models.
We use the Vienna ab-initio simulation package (VASP). The strong Coulomb interaction among 3d electrons in Mn ions is taken into acount by local spin density approximation (LSDA) + U method. We adopted 28 doping models of the La0.75Ca0.25MnO3 four-layered slab and analyzed atomic and electronic strucutres of 3 typical models (see Fig. 2). Since the samples are made on SrTiO3(100) substrate in the experiments, we fixed the lattice constants and atomic positions of undermost layer to those determined by experiments. STM images were simulated using the local density of states (LDOS) at 1.5eV below the Fermi level and at 2 Å from the surface.
Simulated STM image for the most stable model (See Fig. 3) shows the same zigzag tendency as the experimental ones. This trend can be understood by the reconstruction of the coordinated O atoms around Mn. Some of the unstable doping models do not show the zigzag tendency because of large surface distortion due to the Ca dopant near the surface.
The stable doping model also reproduces the insulating nature of surface. On the other hand, layer projected density of states show no band gap for the inner layers of the slabs. Structural analysis together with the charge analysis suggests that this difference is led by the surface reconstruction around the Mn atoms.

Figure 1
The Aprotic Lithium-Air Battery: New Insights into Materials and Reactions
Authors: Mahne Nika , Müller Tobias , Breuer Stefan , Chen Yuhui , Johnson Lee , Fontaine Olivier , Bruce Peter G , Freunberger Stefan A 
Published: February 2020

In the long term high-volume applications such as electric vehicles and the storage of electricity from renewables require a step change in energy density, material sustainability and cost that stepwise improvement of current Li-ion technology based on intercalation electrodes cannot hope to deliver. Radical new approaches are required, motivating ambitious and potentially game-changing research ‘beyond intercalation chemistries’. One such alternative is the Li-air(O2) battery; its theoretical specific energy exceeds that of Li-ion, but many hurdles face its realization.[1-3] First, the processes that occur in the cell on discharge and charge need to be understood to use such knowledge to address the hurdles.
The discharge reaction in the cathode of the nonaqueous Li-O2 cell involves reduction of O2 and the formation of solid Li2O2; the process is reversed on charge, O2 + 2 Li+ + 2 e– « Li2O2. It is now understood that parasitic reactions are a major cause for overpotentials on discharge and charge and limited cycle life. These are both caused by decomposition of many electrolytes and the cathode. Poor electron transport in Li2O2 is recognized as a major factor limiting its achievable amount during discharge (that is, achievable capacity) and the rate and overpotentials at which it can be formed and decomposed during cycling[4-6]. A further major challenge is extended cyclability at desirable deep discharge. We will discuss recent insights into the mechanism of Li2O2 formation and decomposition, of parasitic reactions and novel electrode and electrolyte materials.
[1] P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J.-M. Tarascon, Nature Mater.
11 (2012) 19.
[2] J. Christensen, P. Albertus, R.S. Sanchez-Carrera et al., J. Electrochem. Soc.
159 (2012) R1.
[3] Y.-C. Lu, B.M. Gallant, D.G. Kwabi et al., Energy Environ. Sci.
6 (2013) 750.
[4] Y. Chen, S.A. Freunberger, Z. Peng, O. Fontaine, P.G. Bruce, Nature Chem.
5 (2013) 489.
[5] A. Dunst, V. Epp, I. Hanzu, S.A. Freunberger, M. Wilkening, Energy Environ. Sci.
7 (2014) 2739.
[6] L. Johnson, C. Li, Z. Liu et al., Nature Chem.
6 (2014) 1091
A Spectroelectrochemical Study of Oxygen Electrode Reactions in Dimethyl Sulfoxide Electrolyte for Aprotic Li-O2 Batteries
Authors: Peng Zhangquan , Zhang Xinmin , Zhang Yelong , Bruce Peter G 
Published: February 2020

Due to their high theoretical energy density, Li-O2 systems based on aprotic electrolytes have attracted a great deal of interest in the past few years.1-3 Operation of an aprotic Li-O2 battery critically relies on the reversible and efficient oxygen electrode reactions occuring in the positive electrode.4,5 Therefore, it is important to understand the oxygen reaction mechanisms at the positive electrode/Li+ electrolyte interface. Here, we report a mechanistic study of a model system, i.e., oxygen reactions on an Au electrode in a Li+dimethyl sulfoxide (DMSO) electrolyte with a range of complementary techniques. By spectroscopically identifying the reaction products and intermediates, coupled with electrochemical measurements under well-defined conditions, oxygen reaction pathways and the rate limiting steps were depicted.

References

[1] Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nat. Mater.
2012, 11, 19-29.
[2] Lu, J.; Li, L.; Park, J.-B.; Sun, Y. -K.; Wu, F.; Amine, K. Chem. Rev.
2014, 114, 5611-5640.
[3] Luntz, A. C.; McCloskey, B. D. Chem. Rev.
2014, 114, 11721–11750.
[4] Peng, Z.Q.; Freunberger, S. A.; Chen, Y.; Bruce, P. G. Science
2012, 337, 563-566.
[5] Peng, Z.Q.; Zhang, X.M.; Zhang, Y.L.; Bruce, P.G. manscirpt in preparation.
Revealing Conduction Mechanisms in Lithium-Rich Garnets Using Aliovalent Dopants
Authors: Brugge Rowena Helen , Aguadero Ainara , Kilner John A. 
Published: February 2020

Lithium stuffed garnets such as Li7La3Zr2O12 (LLZO) show promise as solid state lithium ion conductors for use in high energy density storage applications due to their chemical and thermal stability and electrochemical performance versus current technology electrolytes. Much work has focused on improving the conductivity of these systems by optimizing the lithium content in the cubic garnet phase rather than the less conducting tetragonal polymorph1.
Despite extensive studies on these materials, there is uncertainty as to the preferred migration of Li; whether the ions move from one octahedral (Oh) site to another via a neighbouring tetrahedron (Oh-Td-Oh path), or hop directly across Oh sites, bypassing the Td site (Oh-Oh path), is still up for debate2,3.
We seek to confirm the lattice site occupancy of the mobile lithium ions and their associated conduction pathways by varying the lithium-substituted dopant species (Ga, Zn, Ge), thereby blocking Li movement through one of the two paths. The effect of dopant charge and ionic radius on cubic phase stabilization (as a result of Li concentration) and lattice strain is studied.
Moreover, the moisture sensitivity of Li-conductor ceramics has been recently associated with a deterioration of Li transport4 and density of the material, of great importance in battery applications5. In this study, we use an argon-supplied glove box coupled to a furnace for processing and synthesis, preventing proton exchange with Li, thus avoiding the creation of proton charge carriers and improving the densification to above 90% relative density. This is fundamental to analyze the real Li-conduction mechanism and optimize the Li conductivity in garnets. To study the degradation process of lithium displacement by protons in moisture, and the effect of the protons on the ionic conductivity, we conduct isotopic exchange experiments on the samples using H2O and D2O followed by secondary ion mass spectroscopy. The total conductivity of the samples is found by AC impedance in a range of humidities and temperatures. X-ray diffraction and neutron diffraction are employed to determine the structural features, specifically to localize the dopants, Li and protons and to analyse the conduction pathways as a function of the dopant.
References

1J. Awaka et al.(2009) J. Solid State Chem. 182, 2046-2052

2 Han, J. et al. (2012) Chem. Commun., 48 (79), 9840–9842

3 Xu, M. et al. (2012) Phys .Rev. B, 85, 052301

4Aguesse, F. et al. (2014) Adv. Mater. Interfaces, 1 (7), 1300143

5 Bernuy-Lopez, C. et al. (2014) Chem. Mater., 26 (12), 3610-3617

Figure 1
Non-Aqueous Ionic Liquid Energy Storage Systems
Authors: Sutto Thomas Edward 
Published: February 2020

Our research has focused on the use of ionic liquids based on acetate, trifluoroacetate, hydrogen sulfate and oxalate as new types of electrolytes for non-aqueous energy storage systems. Electrodes studied have included MnO2, Ag2O, as well as Zn and Sn. Additionally, work has begun on studying the interactions of VOx electrolytes for a rechargeable V-O battery. Results will show progress towads making not only simple primary batteries, but also re chargeable systems as well.

Figure 1
New Oxide Catalyst Support Generation for PEFC - Application in Meas, Performance and Stability Issues
Authors: Patru Alexandra , Fabbri Emiliana , Kötz Ruediger , Schmidt Thomas J. 
Published: February 2020

The stability of fuel cell performance still remains a significant challenge for polymer electrolyte fuel cell (PEFC) technology. The well-known carbon corrosion degradation process [1] leads to an intense research for an alternative catalyst support materials. One of the actual trends in this field is focused on conductive metal oxide development, as they can exhibit a high electrochemical stability when used in their highest oxidation states, and can be tailored with a high specific surface compatible with the targeted PEFC application.
Up to date, the literature reports stability studies for new oxide catalyst supports but the degradation protocols are realised at the laboratory level (typically room temperature, high potential range, non-optimised catalytic layer) [2]. Only few data are available regarding the processing of these new alternative supports for Pt in a PEFC and their stability under real working conditions of the derived MEAs.
For this purpose Pt/IrTiO2 and Pt/Sb-doped SnO2 (SbSnO2) catalysts were studied. Pt/IrTiO2 provided by Umicore® was used as a model catalyst, whereas Pt/SbSnO2 catalyst was synthesized in our laboratories. For this purpose, a SbSnO2 powder was first synthesized by a modified sol-gel method. Platinum nanoparticles obtained by the polyol method [4] were further deposited on this oxide support. Different cathodes were prepared by direct spraying of optimised suspensions of Pt/IrTiO2 and Pt/SbSnO2 catalyst nanoparticles on a Nafion® XL-100 membrane.
The fuel cell performances and stabilities of the various membrane-electrode assemblies are examined in details. The results are compared with the MEAs based on the state of the art Pt/C (46%wt on High surface area carbon, Tanaka) catalyst and prepared by the same spraying procedure.

Acknowledgement

The authors thank Umicore AG & Co KG and the Competence Center for Energy and Mobility (CCEM) Switzerland for their financial support within the project DuraCat.

References

[1] F.N. Buchi, M. Inaba, T.J. Schmidt, editors. Polymer Electrolyte Fuel Cell Durability, Springer(2009).
[2] Y. Takabatake, Z. Noda, S.M. Hayashi, K. Sasaki, International Journal of Hydrogen Energy 39, 5074-5082 (2014).
[3] E. Fabbri, A. Rabis, R. Kötz, T. J. Schmidt, Physical Chemistry Chemical Physics 16, 13672-13681 (2014).
[4] E. Fabbri, A. Patru, A. Rabis, R. Kötz, T. J. Schmidt, Chimia 68, 217–220 (2014).
Thin, Robust, Stable, High Performance Anion Exchnage Membranes for Elecrochemical Energy Conversion Applications
Authors: Herring Andrew M , Maes Ashley M , Sarode Himanshu N , Liu Ye , Pandey Tara P , Caire Benjamin R , Liberatore Matthew W , Coughlin E. Bryan , Di Noto Vito 
Published: February 2020

The potential of anion exchange membrane (AEM) fuel cells to provide inexpensive compact power from a wider variety of fuels than is possible with a proton exchange membrane (PEM) fuel cell, has continued to drive the research interest in this area. Alkaline catalysis in fuel cells has been demonstrated with non-precious metal catalysts, and with a variety of fuels beyond H2 and methanol. Alkaline fuel cells (AFCs), based on aqueous solutions of KOH, have serious drawbacks associated with system complexity and carbonate formation. Anion exchange membrane (AEMs) fuel cells have a number of advantages over both PEM fuel cells and traditional AFCs; however, although anionic conductivity in AEMs can be comparable to PEMs the chemical stability of membrane attached cations in hydroxide is still not always sufficient for practical applications. The real issue is water transport; water is both a product and a reactant in these systems and wet cations are much more stable than dry. Wetted cations are alos much more stable than dry cations. So an understanding of water in these membranes is essential.
Here we discuss water and anion transport in a series of thin mechanically robust state of the rt experimental anion exchange membranes. The membranes are generally constructed from an isoprene block and a vinyl benzyl bromide block, either randomly or in di-, tri- or penta- block configurations. Post quaterniaztion leads to functionalized AEMs. We use electrochemical impedance spectroscopy to measure anion conductivity, multi-nuclear pulse field gradient spin echo NMR to measure self-diffusion, and broadband electric spectroscopy to measure the relaxation processes in these polymers. This information is coupled with microscopy and SAXS to explore the polymer morphology. Putting transport and morphology together allows us to describe a complete picture of water and anion transport in these systems.
We have begun to build direct fueled AEM fuel cells and electrolyzers for hydrogen and ammonia production from these membranes and their related ionomers. We will alos show a few examples of the AEMs practical uses in single cell devices in this talk.
Spinel MnO2 As a Rapidly Oxidizing Cathode Material for Fuel Cell/Battery Systems
Authors: Musil Mike , Choi Bokkyu , Panthi Dhruba , Tsutsumi Atsushi 
Published: February 2020

The fuel cell/battery (FCB) system combines the working principle of an alkaline battery with an alkaline fuel cell. As anode material, a metal hydride is chosen, which is also found in nickel-metal hydride batteries. This mischmetal can be charged both electrochemically and under hydrogen atmosphere. As a cathode material, manganese dioxide (MnO2) is utilized. We have shown previously that MnO2can, under the right conditions, be cycled electrochemically and recharged from its discharged form (MnOOH) via oxidation in an oxygen saturated alkaline solution.
MnO2 can have different crystalloid structures, depending on the allocation of the MnO6 octahedra. In previous work, we have mostly focused on electrolytic manganese dioxide (EMD), also called γ-MnO2, in which the MnO6 octahedra are aligned to create a combination of 2x1 and 1x1 tunnel structures. In this work, however, we investigated the possibility of utilizing spinel MnO2, also known as λ-MnO2, as an alternative
To obtain λ-MnO2, we first synthesized LiMn2O4 via a solid state reaction of EMD with LiOH. The result was a spinel structure with Li+ ions occupying the tetrahedral sites. The lithium ions can then be removed chemically in a diluted acid, thereby leaving the solid in a spinel structure. We then analyzed the performance of λ-MnO2 for the application in FCB and compared it with γ-MnO2. For this, we manufactured half-cells, cycled the samples electrochemically and recharged MnOOH in an oxygen-saturated alkaline solution in an autoclave.
The cathodes were manufactured through a pasting method with a slurry consisting of MnO2, carbon black (CB) and ethylene-vinyl acetate (EVA) in a weight ratio of 100:15:10 dissolved in xylene. Half-cells were assembled with nickel foam and Hg/HgO as counter and reference electrode, respectively, polypropylene as separator and a 6M KOH solution as electrolyte.
Compared with γ-MnO2, λ-MnO2 shows a similar capacity during the first discharge, but loses a high capacity between the first and second discharge. Afterwards, capacity loss is considerably lower and at around the same rate as for γ-MnO2. However, in terms of rechargeability with oxygen, λ-MnO2 shows superior results. In an oxygen-saturated 6M KOH solution under 1MPa pressure, after 1 hour, the fully discharged λ-MnO2 recharged to 15% of its maximum theoretical capacity, compared to 10% of γ-MnO2.
These are very promising results on our target of combining the advantages of fuel cells with batteries. Further research is thus being conducted, mainly focusing on improving rechargeability of λ-MnO2.