bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitride-Based Sacrificial Cathode Additive for High Energy Density Lithium-Ion Batteries
Authors: Yun Dongyeon , Kim Juhwan , Hong Seung-Tae
Published: December 2024

Lithium-ion batteries are indispensable in modern technology, powering a vast range of applications from electric vehicles to mobile devices, and are pivotal in the pursuit of sustainable energy solutions. Enhancing their energy density is of particular importance, and silicon-based anode materials are at the forefront due to their superior capacity over conventional graphite anodes. However, the use of silicon-based materials as anodes leads to substantial lithium consumption during the initial solid electrolyte interface (SEI) layer formation. Consequently, this results in a significant first cycle Coulombic efficiency gap between the conventional cathode Li(NixMnyCoz)O2 (NMC) material and the anode, leading to inefficient use of the available lithium and a failure to harness the maximum capacity of the electrode materials.

To address this irreversible capacity loss and to fully exploit the capacity of NMC cathode materials, the development of innovative sacrificial additives for prelithiation is critical. Such additives, included within the positive electrode, provide additional lithium to the anode during the initial charging cycle. Our study introduces a novel lithium nitride-based material, distinguished by its high initial compensation capacity and chemical stability in dry-air conditions. This material exhibits an impressive initial charging capacity of over 600 mA·g−1 and a minimal discharge capacity of less than 20 mA·g−1. These characteristics significantly boost the reversible capacity of a full cell that combines an NMC cathode and silicon-based anode. We will detail the synthesis, crystallographic details, and comprehensive chemical and electrochemical characterizations of this promising sacrificial cathode additive, highlighting its potential to enhance battery performance significantly.
First-Principles Study on Lithiation Process of Sio Anode for Li-Ion Batteries
Authors: Shintaku Ryoya , Tamura Tomoyuki , Nogami Shogo , Hirose Takakazu
Published: December 2024

Lithium-ion secondary batteries (LIB) with a high energy density have been developed mainly for use in small mobile devices. In recent years, the high capacity of LIB has become important for automobile applications. One possible high-energy density solution is the use of high-capacity negative electrodes fabricated from tin, silicon, or other materials, and a-SiO materials have been already commercialized. However, a-SiO materials has the issue of capacity degradation during charge-discharge cycles. In particular, it is speculated that the structural change during charging process causes the capacity degradation, but the detail has not been clarified yet. Therefore, in this study, we clarify the local structural changes in a-SiO up to full charge using first-principles calculations.

In our previous study [1], a-SiO models were generated using classical molecular dynamics (MD) simulations with neural network potentials.

Using one of these models, we explore the lithiation process of a-SiO using first-principles calculations with SIESTA code [2]. The simplest method to obtain a-Li
x
SiO model is to melt an initial structure in which Li atoms are randomly arranged at high temperature and then cool it. But it was found that this process could not reproduce the actual charge process and Li atoms should be placed at stable sites. Therefore, we developed a computational code with which stable sites of Li atoms can be searched efficiently using Bayesian optimization.

Fig. 1 shows Li-inserted models at (a) 0%, (b) 55% and (c) 100% SoC (State of Charge). Li atoms are gradually inserted into the SiOx phase in the initial state of charging, and inserted into the Si phase over 20% SoC. These results are consistent with previous experimental results [3]. One Li6O octahedron can be seen in the model at 55% SoC, and the number of Li6O octahedra increases to five in the model at 100% SoC. The formation of Li6O octahedra during charging is irreversible, which is considered to cause the capacity degradation. To prevent capacity degradation, it is necessary to suppress the formation of these structures.

References

[1] H. Hirai et al., Phys. Rev. Materials 6, 115601 (2022).

[2] J. Solar et al., J. Phys. Cond. Matt. 14, 2745 (2000).

[3] T. Hirose et al., Solid State Inonics 304, 1 (2017).

Figure 1
Ion Transport and Solution Behavior of Polyanion-Type Li Salts in Nonaqueous Solvents
Authors: Nakagaki Hiroki , Kondou Shinji , Watanabe Masayoshi , Ueno Kazuhide
Published: December 2024

To achieve fast charging and discharging of Li-ion batteries, it is important to improve the ionic conductivity (σ) of the electrolyte as well as the Li-ion transference number (t
Li) [1]. While nonaqueous polyelectrolyte solutions exhibit high Li-ion transference number(t
Li
= 0.81) upon immobilization of the anion on a polymer backbone, the ionic conductivity (σ = 1.3 mS cm-1) is inferior to that of conventional electrolytes (σ ~10 mS cm-1). One of the reasons for the low ionic conductivity is low dissociation degree caused by the counter-ion condensation on the polymer backbone. To gain an insight into a design strategy of polyelectrolyte-based liquid electrolytes for LIBs, we studied the effects of polyelectrolyte structure and solvent polarity on the transport properties and Li-ion solvation of the polyelectrolytes in carbonate solvents. Here, we employed two polyelectrolyte copolymers with different sequences; random copolymers of the Li salt of a weakly coordinating polyanion, poly[(4-styrenesulfonyl)-(trifluoromethanesulfonyl)amide] (poly(LiSTFSA)) with neutral comonomer unit, and poly[(4-maleimide-N-[(trifluoromethyl)sulfonyl]-benzenesulfonamide lithium salt] (poly(sa-PMI))-based alternating copolymers with neutral comonomer unit. For the random copolymers, the ionic conductivity increased as the ratio of the neutral comonomer increased. This was attributed to the suppression of counter-ion condensation and increased dissociation. The alternating copolymer solution showed higher dissociation than the random copolymers. The highest ionic conductivity was unexpectedly observed for the lowest polar mixture (such as a dimethyl carbonate rich mixture) at the highest salt concentration despite the low dissociation degree of the polyelectrolytes. A unique conduction resulting from the faster diffusion of transiently solvated Li ions along the interconnected aggregates of polyanion chains was suggested in the highly concentrated polyelectrolyte solutions in low polar solvents. A Li/LiFePO4 cell using the polyelectrolyte solution demonstrated a good charge-discharge performance and rate capability[2].

References

[1] K. M. Diederichsen, E. J. McShane, B. D. McCloskey, ACS Energy Lett., 2, 2563-2575 (2017).

[2] S. Kondou et al., ACS Appl. Mater. Interfaces, 14, 18324-18334 (2022).
Observation of Excited State-Derived Photoluminescence Decay of Organic Dye to Monitor Its Photo-Induced Charge Transfer Efficiency
Authors: Shin HyeonOh , Kwon Tae_Hyuk
Published: December 2024

Understanding photo-induced charge transfer (PCT) is crucial for optimizing the performance of solar-powered devices like photovoltaic and photoelectrochemical cells, as PCT directly impacts their operation and overall power conversion efficiency. General assessment of PCT has heavily relied on transient absorption techniques to gauge electron transfer between the donor and acceptor. However, there is a pressing need to broaden the methods for comprehensively studying PCT.

In this study, we propose an alternative approach utilizing transient photoluminescence to observe PCT dynamics between organic dyes and redox mediators. This approach involves adsorbing various organic dyes onto Al2O3 surfaces along with redox mediators. When excited, the dyes facilitate charge separation from each other, leading to the instantaneous oxidized form of the dye and subsequent electron transfer from the redox mediator. This process results in a decrease in the photoluminescence lifetime of the organic dye. The extent of this decreases correlates with the Gibbs free energy of charge transfer, reflecting the efficiency of electron transfer between the organic dye and the redox mediator. Our findings introduce an alternative avenue for studying PCT, offering insights that are pertinent to various fields including photovoltaics, optoelectronics, and photocatalysis.

Figure 1
Redox Behavior of Quinones Bearing Ionic Liquid Moiety for Electrochemical CO2 Capture
Authors: Fujisawa Takuma , Tsuzuki Seiji , Watanabe Masayoshi , Ueno Kazuhide
Published: December 2024

CCUS (Carbon dioxide Capture, Utilization and Storage), is attracting attention as an effective method for reducing carbon dioxide (CO2) emissions toward carbon neutrality by 2050. Currently, chemical absorption followed by thermal desorption using liquid amine is employed as the CO2 capture and concentration technology. However, low energy efficiency and high cost of the thermal swing process remain to be addressed. CO2 capture driven by renewable electricity represents a promising alternative approach to mitigate CO2 emissions and address climate change. Electrochemically mediated carbon capture can be achieved by developing redox-active CO2 adsorbents, such as quinones. In aprotic electrolytes, reduced quinone species can selectively uptake CO2 from a dilute feed upon electro-reduction via a nucleophilic addition reaction and release a concentrated CO2 upon electrochemical oxidation. However, the low solubility of quinones in nonaqueous solvents limits their total CO2 carrying capacity in the system. We synthesized a salt of imidazolium modified anthraquinone with ionic liquid-like structure to address the solubility issue. The synthesized cationic quinone derivatives showed more than 100 times higher solubility and high ionic conductivity as well as electrochemically reversible CO2 adsorption-desorption. In addition, we synthesized anionic quinone derivatives, anthraquinone with sulfonate (SO3
−) moiety, by one-step salt metathesis reaction, and confirmed that the negatively charged quinones is also applicable to the electrochemical CO2 capture. We report the electrochemical CO2 capture-release behaviors of the ionic quinones and its monitoring using in situ spectroscopic analysis with the aid of density functional theory calculations.

Reference:

Iida, S. Kondou, S. Tsuzuki, M. Tashiro, N. Shida, K. Motokura, K. Dokko, M. Watanabe, K. Ueno, J. Phys. Chem. C, 2023, 127, 10077.
Electrochemical Studies on CO2 Reduction at Liquid Gainsn Alloy Electrodes
Authors: Bogdanoff Peter , Mohamed Aya , Lörch Daniel , Euchner Holger , May Matthias , van de Krol Roel
Published: December 2024

The electrochemical reduction of CO2 (CO2RR) offers a sustainable technology for converting CO2 into valuable products when using electricity generated from renewable sources. Application-oriented research is currently focused mainly on the electrolysis of CO2 to hydrogen-rich fuels or chemical feedstock materials. In contrast our project aims to form solid carbon or carbon rich products (e.g. oxalate), which can finally be disposed in geological repositories. This negative emission technology is developed for a long-term and thereby sustainable CO2 removal from the global CO2 cycle 1. The continuous electrochemical formation of solid carbon from CO2 has so far only been reported on liquid GaInSn-M alloys (M: Ce, V) in water-containing DMF 2,3. Liquid electrodes have the advantage over solid electrodes that solid products do not adhere at the interface and therefore deactivate the catalytic properties of the electrode (coking effect). In first experiments, we studied GaInSn without additional metal alloying in DMF/H2O/ TBAPF6 electrolyte and got differing results to the previously published data. In our experiments, even pure GaInSn shows a significant activity for CO2RR to carbon monoxide and formic acid accompanied by lower quantities of H2. The product distribution (faradaic efficiencies) depends strongly on the water content in the DMF electrolyte. The production rate of CO increases significantly even with small amounts of water. First DFT simulations of the CO2RR provide possible explanations of this effect. Furthermore, it was observed that, depending on the applied cathodic potential, metallic nano particles are released from the GaInSn surface into the organic electrolyte (expulsion effect) which indicates a possible change in the surface composition during CO2 electrolysis 4. In accordance with the literature, our findings confirm the production of carbon flakes from CO2 on cerium modified GaInSn. However, we observe it even independently from the addition of water to the DMF electrolyte. DFT calculations enable us to conclude that the high affinity of cerium to oxygen is responsible for the change in product selectivity, as it can extract oxygen from CO2.

1: May, M. M. and Rehfeld, Earth Syst. Dynam., 10, 1–7.

doi.org/10.5194/esd-10-1-2019, 2019.

2: Dorna Esrafilzadeh, NATURE COMMUNICATIONS | (2019) 10:865.

doi.org/10.1038/s41467-019-08824-8

3: Mehmood Irfan, J. Mat. Chem. A, Issue 27, 2023

doi.org/10.1039/D3TA01379K

4: Mahroo Baharfar, Chemistry of Materials
2022
34 (23), 10761-10771

doi.org/10.1038/s41467-019-08824-8

Figure 1
Homoleptic and Heteroleptic Coordination Environment of Palladium Molecular Catalysts for Oxygen Reduction to Hydrogen Peroxide
Authors: Moges Endalkachew Asefa Asefa , Tsai Meng-Che , Su Wei-Nien , Hwang Bing Joe
Published: December 2024

Hydrogen peroxide (H2O2) serves a wide range of purposes in industries such as chemical manufacturing, energy production, and wastewater treatment, either alone or in combination with other oxidizers. The demand for H2O2 has seen a notable increase due to its heightened use in disinfection amid the COVID-19 pandemic. Currently, industrial synthesis of H2O2 relies on anthraquinone technology, a complex process involving multiple steps including the use of H2 gas, transfer of H2O2 between solvents, distillation of concentrated H2O2, and potentially hazardous transportation. Thus, advancements in developing efficient and selective electrocatalysts for the two-electron oxygen reduction reaction (2e- ORR) are crucial for promoting the adoption of electrochemical synthesis of H2O2 production. In our study, we synthesized single-atom electrocatalysts—Pd-N4-CO, Pd-S4-NCO, and Pd-N2O2-C through an in-situ synthesis approach involving heteroatom-rich ligands and activated carbon under mild reaction conditions. These catalysts feature both homoleptic (Pd-N, Pd-S) and heteroleptic (Pd-NO) coordination spheres, which are expected to demonstrate selectivity in the two-electron/four-electron pathway of the oxygen reduction rection (ORR). Moreover, the coordination of the Schiff base and poly pyridyl ligands to the palladium atom could be observed via the thiol ligand (Pd-S4-NCO), azomethine nitrogen and hydroxyl oxygen atoms (Pd-N2O2-C), and the pyridinic nitrogen atom of 1,10-phenathroline-5,6-dione (Pd-N4-CO). Notably, Pd-N4-CO shows promise as an electrocatalyst for two-electron ORR, facilitating green H2O2 production with high activity and selectivity in a basic electrolyte, exhibiting minimal onset overpotential and over 95% selectivity across various potentials. The electrocatalysts performance in ORR follows Pd-N4-CO > Pd-N2O2-C > Pd-S4-NCO, aligning with the Pull-Push mechanism. This mechanism underscores the significance of strong coordination of Pd with electronegative donor atoms like N and O, and weak coordination with intermediate *OOH, enhancing selectivity and green H2O2 production. Our findings, both experimental and DFT calculations, offer new insights into engineering heteroatom-rich ligands to tune the electronic structure of catalytic active sites. This understanding informs the atomic-level structure-activity and selectivity relationship, facilitating the development of more effective and efficient catalysts for the electrochemical synthesis of hydrogen peroxide.
Large-Scale DFT Calculations on Size and Site Dependences of Atomic and Electronic Structures in Metallic Nanoparticle Catalysts
Authors: Nakata Ayako , Li Shengzhou , Miyazaki Tsuyoshi
Published: December 2024

Size control of Pt nanoparticle catalysts is one of the key challenges in fuel cell development. Miniaturization of Pt nanoparticles is expected to increase activity and save the amount of Pt, while very small particles (e.g. sub-nano particles or clusters) have different electronic structures and stabilities from “nano” particles. To investigate the atomic and electronic structures of materials, first-principles density functional theory (DFT) calculation is a powerful tool. However, because of its high computational cost, the DFT applications have been limited mainly for small particles and clusters of tens to hundreds of atoms. In this study, by using our own large-scale DFT calculation method, we investigate the size and site dependences of atomic and electronic structures in Pt nanoparticles with the diameters of several nanometers, which are comparable to the sizes of the particles in practical use.

The computational cost of the conventional DFT calculation methods scale cubically to the system size, i.e., the number of the atoms in the target system and the number of local functions for each atom, which are used to express electronic density. We have developed the multi-site support function (MSSF) method [1,2], in which local functions are constructed as the linear combinations of the atomic orbital functions belonging to not only the target atom but also its neighboring atoms. The MSSF method enables us to reduce the number of local functions to be the minimal-basis size, leading the dramatical computational cost reduction. The MSSF method is implemented in our large-scale DFT code CONQUEST [3,4].

We optimized the structures of Pt nanoparticles with the diameters of 0.5 nm (13 atoms) - 5.5 nm (3871 atoms) and found that the Pt-Pt bond lengths inside the nanoparticle converge to those in bulk Pt when the nanoparticle size becomes large. The similar trend is found also in the electronic structures as shown in the figure. In the presentation, we compare the size dependence of the stability and atomic and electronic structures of Pt nanoparticle with other metallic nanoparticles. Site dependence of the electronic structures and reactivity with molecules are also investigated by using large-scale DFT together with statistical analysis.

[1] A. Nakata, D. R. Bowler, T. Miyazaki, J. Phys. Soc. Jpn., 91, 091011 (2022). [2] A. Nakata, D. R. Bowler, T. Miyazaki, Phys. Chem. Chem. Phys. 17, 31427 (2015). [3] http://www.order-n.org/ [4] A. Nakata, J. S. Baker, S. Y. Mujahed, J. T. L. Poulton, S. Arapan, J. Lin, Z. Raza, S. Yadav, L. Truflandier, T. Miyazaki, D. R. Bowler, J. Chem. Phys., 152, 164112 (2020).

Figure 1
Electrode-Level Modeling of Silicon Anodes for Improved Design
Authors: Shumway Edmund McKay , Hamedi Amir Sina , Wheeler Dean
Published: December 2024

Silicon is an ideal active material for lithium-ion battery anodes, due to its low potential and high theoretical capacity. However, extreme volume changes during lithiation and delithiation make reversibility and long cycle life difficult challenges. To properly understand these volume changes, a detailed electrochemical model is needed. Much previous modeling work has focused on particle-level effects such as intra-particle diffusion and cracking. Beyond this, some efforts have successfully utilized pseudo-2-dimensional (P2D) models to evaluate electrode-level phenomena — such as stress distribution and changes in electrode thickness and electrochemical potential. Nevertheless, some essential physics is still missing.

Here, we present a new P2D model with improvements that provide a deeper level of understanding of porous silicon anode property changes during lithiation, to enable improved electrode design. Important among these improvements are the use of local state of lithiation as opposed to electrode average state of lithiation to better capture porosity and ionic conductivity changes; an effective electrolyte reservoir that properly addresses electrolyte volume-change requirements; advection of electrolyte and solid-state Li; and an extensive electrode-level plastic deformation model that has a dramatic effect on the model’s predictions.

We use this model to test the efficacy of various electrode and cell design decisions. The model can make recommendations on casing design such as rigidity and thickness and the effect of other cell sandwich components e.g. different layers thickness on the electrochemical performance of the cell. Furthermore, using the revised swelling behavior predictions given by the mechanical model, we can provide recommendations for initial electrode porosity and binder volume fraction. Finally, the model as a whole allows us to provide recommendations that will accommodate particle expansion with the least detriment to ionic conductivity at various C-rates.

Figure 1
State of Charge When Cycling LiFeO4/Graphite Cells Affects Lifetime
Authors: Zsoldos Eniko , Thompson Daphne , Black William , Azam Saad , Dahn Jeff R.
Published: December 2024

Lithium iron phosphate (LFP) battery cells are used ubiquitously in electric vehicles and stationary energy storage because they are cheap and have a relatively long lifetime, but they have low energy and power density1. This work compares the LFP / Graphite pouch cells undergoing charge-discharge cycles over three state of charge (SOC) windows: 0 – 25%, 0 – 100%, and 75 – 100%. Cycling LFP cells across a lower average SOC provides longer cell lifetime than a higher average SOC, regardless of depth of discharge. There are two capacity fade degradation mechanisms that are prominent at high SOC: iron dissolution and deposition onto the negative electrode, and lithiated graphite reactivity with electrolyte increasing incrementally with SOC and with the amount of deposited Fe. It is commonly known that cell voltage and depth of discharge should be minimized to improve lifetime, but this is based on cell types that operate at higher voltages than 3.65 V in LFP/AG cells. Our results show that even low voltage LFP systems have this trade-off between state of charge and lifetime. We show that the average SOC of operation is more critical for capacity fade than the variables of electrolyte salt choice (LiPF6 vs LiFSI), graphite choice or temperature (40°C vs 55°C). This work employed isothermal microcalorimetry to investigate the heat flow from lithiated graphite-electrolyte reactivity2, scanning micro-xray fluorescence to quantify iron deposition on the negative electrodes3, and liquid electrolyte analysis techniques NMR and GC-MS to investigate electrolyte degradation products.

Figure 1: LFP/AG pouch cell cycling capacity fade across different SOC ranges in long term cycling over 2500 hours. For best comparison, only the C/20 checkup cycles are plotted, where all cells cycle 0-100% every 100 cycles or every ~300 hours. The regular cycles are at C/3 rate, and only 60 mAh out of 240 mAh nominal are cycled. Discharge capacity vs cycling time is plotted for (a) 40°C and (b) 55°C testing of LFP/AG cells with LiPF6 and LiFSI electrolyte salts at various SOC operation windows. The cell barcode IDs are indicated in the legends. The normalized discharge capacity fade per hour at (c) 40°C and (d) 55°C is summarized after 2500 hours of cycling for the different SOC windows cycled. Electrolyte is EC:DMC 3:7 2VC 1.5M LiFSI or LiPF6.

References:

[1] Safari, M. & Delacourt, C. Aging of a Commercial Graphite/LiFePO4 Cell. J. Electrochem. Soc.
158, A1123 (2011).

[2] Logan, E. R.; Dahn, J. R. Measuring Parasitic Heat Flow in LiFePO 4 /Graphite Cells Using Isothermal Microcalorimetry. J. Electrochem. Soc.
2021, 168 (12), 120526. https://doi.org/10.1149/1945-7111/ac405b.

[3] Eldesoky, A., Logan, E. R., Johnson, M. B., McFarlane, C. R. M. & Dahn, J. R. Scanning Micro X-ray Fluorescence (μXRF) as an Effective Tool in Quantifying Fe Dissolution in LiFePO 4 Cells: Toward s a Mechanistic Understanding of Fe Dissolution. J. Electrochem. Soc.
167, 130539 (2020).

Figure 1
A Discrete Element Analysis of the Mechanical Properties of Lithium-Ion Electrode Layers Linked to Mechanical Degradation
Authors: Lundkvist Axel , Larsson Per-Lennart , Olsson Erik
Published: December 2024

Lithium-ion batteries are a key player in the electrification of the transport sector. One of the main challenges of today’s lithium-ion batteries is the degradation of charge capacity over time. This capacity degradation stems from several phenomena, and chemical degradation has historically been the main focus of investigation. However, the mechanical degradation of the cell also contributes considerably to the charge degradation and is, therefore, a topic of interest. In this work, a framework for modelling the mechanical behaviour of a positive electrode layer within a lithium-ion battery cell has been developed. This framework uses the discrete element method (DEM), which accurately resolves the granular microstructure of the electrode's active layer. This study aims to characterize the electrode layer’s mechanical response, stemming from the active particles’ elastic-plastic nature and the viscoelastic binder domain. The DEM framework links the local contact behaviour of the particles and the binder and the global mechanical response of the full electrode layer. Understanding this link between length scales is a central first step to fully understanding the mechanical degradation behaviours of the electrode. The model is verified against experimental measurements of the electrode layers’ mechanical properties, measured through U-shape bend tests, by Gupta et al. [1]. The in-plane unloading stiffness and the relaxation of the layer were determined in the experiments, both in compression and tension. The experiments indicated that the in-plane stiffness of the layer differed in compression and tension, with an increasing stiffness at increased compression levels. The relaxation of the layer is also measured over a six-hour period. Through our modelling framework, we were able to capture the pressure-sensitive in-plane stiffness and relaxation of the electrode layer. This work lays an excellent foundation for further investigations of the mechanical properties of the active layer and its mechanical degradation mechanisms, such as swelling and fracture of the active particles due to charge cycling.

[1] P. Gupta, I. B. Üçel, P. Gudmundson, and E. Olsson, “Characterization of the Constitutive Behavior of a Cathode Active Layer in Lithium-Ion Batteries Using a Bending Test Method,” Exp. Mech., vol. 60, no. 6, pp. 847–860, 2020, doi: 10.1007/s11340-020-00613-5.
Evaluation of an Ag/AgF Reference Electrode for Electrochemical Measurements of Molten 2LiF-BeF2
Authors: Pickarski Timothy Ryan , Williams Haley , Scarlat Raluca O. , Borrello Michael
Published: December 2024

Despite the wide application of molten fluoride salts, such as 2LiF-BeF2 (FLiBe), as heat transfer fluids, fuel solvents, and fusion blanket materials in advanced nuclear power concepts, the mechanisms of ion transport, speciation, and reaction kinetics in these systems have not been comprehensively characterized. Though electrochemical methods are powerful tools for probing these properties of molten fluorides, current studies are limited by the lack of a reliable thermodynamic reference electrode (TRE) compatible with the fluoride environment. The reference electrode designs used in fluorides can be classified into three main categories: quasi-reference electrodes (qREs), dynamic reference electrodes (DREs), and thermodynamic reference electrodes. qREs and DREs are not well suited to in-line measurements of molten fluorides since the reference redox couple of the noble qRE material cannot be assumed to be constant and the time scale of the DRE’s relaxation of the transient redox system is too short.

Therefore, explorations of the FLiBe system have pursued the development of a TRE which can hold a thermodynamically stable reference potential for an extended time. Current designs using the H2/HF or Ni/Ni2+ couples suffer from either difficult handling of gas electrodes at high temperatures [1] or long equilibriation times. Since pure NiF2 does not melt at reactor operating temperatures (~500-1000°C), the NiF2 used must dissolve into a reservoir of supporting FLiBe, a process which takes over 30 hours. In this study, the performance of a reference electrode using the Ag/Ag+ redox couple is assessed for long-term electrochemical stability. The Ag/AgF system was chosen to address the limitations of the Ni/Ni2+ TRE, as the low melting point of AgF (Tmelt = 435°C) allows for the direct use of the pure salt in the electrode, eliminating the time-consuming dissolution step required for NiF2.

The Ag/AgF TRE was constructed by melting AgF salt into a boron-nitride crucible fitted with a LaF3 fluoride membrane and inserting a silver wire into the salt reservoir. The stability and reproducibility of the electrode potential were evaluated through long-term open circuit potential measurements against a platinum qRE in a FLiBe melt at 600°C. The reversibility of the Ag/Ag+ reaction was assessed using a linear polarization study. Finally, the location of the redox potential was found by comparing the open circuit potential of the Ag/AgF TRE against a beryllium rod electrode. The development of a reliable and easy-to-operate thermodynamic reference electrode will facilitate future studies on the thermochemical properties of molten FLiBe while laying the foundation for advancing in-line monitoring and redox control in nuclear technologies.

[1] Jenkins, Howard W., "Electrochemical Measurements in Molten Fluorides. " PhD diss., University of Tennessee, 1969. https://trace.tennessee.edu/utk_graddiss/3072
Al Electroplating on Etched CFRP Surfaces in AlCl3-EmImCl Ionic Liquids
Authors: Kishi Naoki , Matsushima Hisayoshi , Ueda Mikito
Published: December 2024

Carbon fiber-reinforced plastics (CFRP) are composite materials of carbon fibers and resin. Since it is low in density, high in strength, and high in rigidity, it is used in many applications such as sports fields and automobiles. However, its surface wear resistance is not enough, and it is limited to using it as a material for friction. To improve wear resistance, CFRP surface modification by Al electroplating and surface anodizing were used in this study. Electroplating is one of the low-cost Al plating methods with easy control of plating film thickness. Since the surface consists of highly conductive carbon fibers and low conductive resin, only the carbon fibers are electroplated. In this study, to increase the occupancy of carbon fibers on the surface, the resin in CFRP was dissolved and removed by acid treatment. Then, Al electrodeposition experiments in ionic liquids were also conducted for the surface.

CFRP (PEEK resin) was cut into 2 cm x 5 cm pieces and used as substrates. Surface etching treatments were performed under 5 molL-1 sulfuric acid at 373 K for 10 to 120 seconds. The ionic liquid used in the electrodeposition experiments was a mixture of 1-ethyl-3-methylimidazolium chloride (EmImCl) and AlCl3 at a molar ratio of 1: 2. As an additive, 1,10-phenanthroline was added to the ionic liquid to a concentration of 20 mmolL-1. In the Al electrodeposition experiments, a CFRP plate (before and after surface etching) was used as the working electrode; Al mesh and Al wire were used as the counter and reference electrodes, respectively. For electroplating, the condition was current pulse electrolysis at 20 mA cm-2, duty ratio 0.83, and temperature at 333 K. In the electroplating, applied electric charge corresponds to a targeted theoretical film thickness of 20 µm. The surface morphology of the electrodeposit before and after electrodeposition was observed by Scanning Electron Microscopy (SEM). Surface roughness was also measured using Confocal Laser Scanning Microscopy (LSCM).

In surface observation after the etching of CFRP in 5 molL-1 sulfuric acid at 373 K, the surface became rougher as the etching time was increased. The surface roughness showed little change when the etching time was 60 and 120 s. The Al electrodeposits on the untreated CFRP surface were smooth with a roughness of 0.43 μm. Al deposits on the surface after etching treatment were 2.25 μm for 60 s treatment and 2.27 μm for 120 s treatment. From the SEM observation of the Al electrodeposits, the electrodeposits were formed along the carbon fibers. In addition, some parts with large gaps between carbon fibers were not covered by Al electrodeposits. It was considered this was due to the difficulty of electrolytes with high viscosity to penetrate into the gap.
Dependence of Cation Structures on Electrochemical Polymerization of Aniline in Phosphonium Ionic Liquids
Authors: Hori Katsuki , Ito Daiki , Nawate Shoki , Matsumoto Mitsuhiro , Tsuchida Yusuke , Tsunashima Katsuhiko , Yamada Hirohisa
Published: December 2024

Ionic liquids (ILs) are known to possess unique physicochemical and abundant design properties. When ILs are used as electrolytes in the electropolymerization reactions of aromatic compounds to form conducting polymers, the grown film properties are significantly dependent of the combination of cations and anions. Typical researches on the IL-based electrolytes have been described for nitrogen-based ILs;1) on the other hand, phosphonium-based ILs have also attracted attention in recent years. We have reported the preliminary electrochemical investigation for electropolymerization of aniline (ANi), indicating that the phosphonium ILs were able to be employed as potential electrolytes.2) In this work, various phosphonium ILs ( Fig. 1) including typical two phosphonium ILs such as triethylpenthylphosphonium bis(trifluoromethanesulfonyl)amide (P2225-TFSA) and tributylmethylphosphonium bis(trifluoromethanesulfonyl)amide (P4441-TFSA) 3) are selected for the electrooxidative polymerization of ANi, in order to investigate the influence of the physicochemical properties of the phosphonium ILs on the electropolymerization processes and the grown polyaniline (PANi) films.

The phosphonium ILs were synthesized and purified according to a previously published paper.3) The electrolytes were prepared by adding 2.0 M of ANi monomer and 1.0 M of 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide (HTFSA) as a proton source. The electropolymerization was carried out by cyclic voltammetry (CV) using a three-electrode cell with a platinum disc or an indium tin oxide (ITO) as a working electrode, a Ag/Ag+ as a reference electrode and a platinum wire as a counter electrode (potential sweep rate: 0.1 V s-1, potential range: -0.5~+1.5 V). The morphology of the electropolymerized PANi films on the ITO electrode were observed by scanning electron microscopy (SEM).

Fig. 2 shows the cyclic voltammograms for electrooxidative polymerization of ANi in typical P2225-TFSA and P4441-TFSA. It was found that the P4441-TFSA based electrolyte tended to give relatively low oxidation currents, forming the uniform PANi film on the electrode surface as shown in Fig. 3. The voltammograms for the electropolymerization measured in various phosphonium ILs will be discussed, demonstrating the influence of the transport property of the phosphonium IL electrolytes.

References

[1] K. Sekiguchi, M. Atobe and T. Fuchigami, J. Electroanal. Chem., 557, 1 (2003).

[2] K. Tsunashima, D. Ito, M. Matsumiya and Y. Ono, ECS Meet. Abstr., MA2016-01 1889.

[3] K. Tsunashima and M. Sugiya, Electrochem. Commun., 9, 2353 (2007).

Figure 1
Electrodeposition of Aluminum-Silicon Films in Chloroaluminate Ionic Liquids
Authors: Venkatesh Krishna , Ispas Adriana , Bund Andreas
Published: December 2024

Aluminum and its alloys are interesting materials for the automotive industry due to their relative low density compared to steel. The weight of vehicles can be drastically reduced by utilizing aluminum and its alloys in the construction of their body parts instead of steel. Moreover, we could previously prove in our group that some aluminum alloys, such as Al-Zn, showed improved resistance against corrosion compared to pure aluminum (1) when electrodeposited onto steel substrates. Aluminum-silicon alloys manufactured by casting have excellent mechanical properties and corrosion resistance. However, one of the problems that can occur during the cooling/solidifying phase in casting is the formation of micro- and macropores or the growth of Al-dendrites (2).

An alternative technique to obtain Al-Si alloys is the electrodeposition technique. Due to the negative reduction potentials of both Al and Si, they cannot be electrodeposited from aqueous solution. They can be obtained by electrolysis in molten salt electrolytes at temperatures above 960°C (3).

In this study we investigated the deposition Al-Si alloys at room temperature in 1-ethyl-3-methylimidazolium chloride, [EMIm]Cl: AlCl3 (1:1.5). Different precursors for Si such as SiCl4, SiBr4 and SiI4 were studied. We found that the type of precursor and its concentration influenced the maximum amount of Si in the alloy, as well as the morphology of the layers. Furthermore, the deposition technique (direct current plating or pulse plating) had a significant effect on the quality of the deposits.

Acknowledgments: The authors gratefully acknowledge the financial support of the Federal Ministry for Economic Affairs and Climate Action, BMWK, Germany, within the project CastCo (FKZ 03LB2046E).

R. Böttcher, A. Ispas, and A. Bund, Metals
13(2) (2023) 377

P.D. Lee, A. Chirazi, and D. See, J. Light Met.
1 (2001) 15

O. Awayssa, G. Saevarsdottir, R. Meirbekova, and G. M. Haarberg, J. Electrochem. Soc.
168 (2021) 046506
Ion Transport Properties in Glyme-Based Highly Concentrated Electrolyte with Asymmetric Li Imide Salts
Authors: Matsuyama Yuna , Philippi Frederik , Sudoh Taku , Tsuzuki Seiji , Watanabe Masayoshi , Ueno Kazuhide
Published: December 2024

The spread of electric vehicles is being expanded around the world with the aim of reducing carbon dioxide emissions toward carbon neutrality by 2050. This trend requires even higher performance for Li secondary batteries. Previous research has focused on increasing ionic conductivity of the electrolyte. It is now clear that the Li ion transference number is equally important to further improve the performance of batteries for automotive applications[1]. However, the relationship between the structure of Li salts and ion transport properties is not understood well, and there is no established method to systematically increase the Li ion transference number. Here we show how the structure of the Li salt affects the ion transport properties for an equimolar mixture of a novel Li salt and tetraglyme (G4). We have synthesized a new Li imide salt, Li (N-(trifluoromethyl)sulfonyl)acetamide) (Li[TfNAc]), having both sulfonyl and carbonyl groups. For the novel highly concentrated electrolyte [Li(G4)][TfNAc], we observed a high Li ion transference number of 0.65 at the cost of a low ionic conductivity of 0.21 mS cm−1. This trade-off between ionic conductivity and transference number is in line with previous empirical observations made in our group[2][3]. Ab initio molecular orbital calculations of lithium affinity in comparison with anions in established electrolytes revealed the order [TFSA]− < [BF4]− < [TfNAc]− < [TFA]−, consistent with the qualitative order observed in ionic transport properties. Thus, ion transport is affected significantly by small changes to the anion structure. We observed that the solvate structure of [Li(G4)][TfNAc] is dominated by correlated motion in ion pairs and larger aggregates, in line with previous studies.[3] Based on the concepts of ionicity (inverse Haven ratio) and Onsager transport coefficients[4], we were able to quantify the impact of ion interactions on the macroscopic transport properties.

[1]K. M. Diederichsen et al, ACS Energy Lett., 2017, 2, 2563.

[2]K. Shigenobu, et al., Phys. Chem. Chem. Phys., 2020, 22, 15214.

[3] K. Shigenobu, et al., Phys. Chem. Chem. Phys., 2021, 23, 2622.

[4] Dong, D.; Sälzer, F.; Roling, B.; Bedrov, D., Phy. Chem. Chem. Phy., 2018, 20, 29174.
The Cations Effect on Polymer-Assisted Anti-Crystallization of Alkali Metal Salts
Authors: Goto Takashi , Sudoh Taku , Watanabe Masayoshi , Ueno Kazuhide
Published: December 2024

To realize carbon neutrality, expanding the use of electric vehicles and stationary storage batteries for renewable energy is one of the effective procedures. The demand of rapid charging and discharging of Li-ion batteries continues to grow, but to achieve this, it is essential to improve Li+ transference number (t
Li) of electrolytes as well as improving ionic conductivity (σ
ion)1. Molten Li salts, consisted only of ions, do not cause concentration polarization, so that high Li+ transfer numbers (t
Li ~ 1) have been reported under anion-blocking condition2. Although most Li salts have high melting point (T
m > 100 °C) and are crystalline solids at room temperature, molten Li salt can facilitate formation of interface between electrode and electrolyte owing to the liquid state. Recently, the addition of a small amount of polymers was found to suppress crystallization and produce supercooled liquid (Li-Deeply Supercooled Salt, Li-DSS) that is stable for a long time at room temperature. Li-DSS achieved high t
Li similar to the molten Li salts. In this study, DSSs were prepared with various alkali metal salts (Li, Na, K salts) and polymer to elucidate the effects of cationic and anionic structure on the formation of DSSs. The salts consisting of alkali metal cations and perfluoroamide anions such as (fluorosulfonyl)(trifluoromethansulfonyl)amide (FTA−) and bis (fluorosulfonyl)amide (FSA−), which have a relatively low melting point and low crystallinity, were selected. For polymer, we selected poly (methyl methacrylate) (PMMA), which is an amorphous polymer and has coordination sites with alkali metal cations. We could obtain Li-, Na-, and K-DSS with the addition of a small amounts of PMMA, but the stability (lifetime) of the supercooled state was in the order Li-, K-, Na-DSS, which did not follow the order of the ionic radius. The effects of cation on the thermal properties and ionic conductivity were also discussed.

Acknowledgement

This study was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA-Next) of the Japan Science and Technology Agency (JST).

References

M. Diederichsen, E. J. McShane and B. D. McCloskey, ACS Energy Letters, 2017, 2, 2563-2575.

Kubota and H. Matsumoto, The Journal of Physical Chemistry C, 2013, 117, 18829-18836.
Enhancing Interfacial Capacitance Using Anionic Amphiphiles in Ionic Liquid Electrolyte Blends
Authors: Tupkar Hrishikesh , Verich Jack , Alemdar Sila , McAlpine Jack , Gebbie Matthew A.
Published: December 2024

The acceleration of climate change due to carbon emissions has generated an imminent need to transition towards renewable energy sources. However, the intermittent nature of renewable sources like wind or solar energy necessitates breakthroughs in energy storage devices that can rapidly charge and discharge. This demand creates a new role for high power density supercapacitors. While supercapacitors can quickly discharge electricity, they are limited by low energy densities. This limitation in energy density has generated research interest into charge storage mechanisms at interfaces and new types of supercapacitor electrolytes. An ideal supercapacitor electrolyte has a wide electrochemical stability window and high capacitance to maximize the energy density. Ionic liquids (ILs) show potential for this role with their wide electrochemical stability windows, nonflammability, and nonvolatility. Problematically, strong ion correlations present in ILs result in low capacitances. I will discuss our work aimed at tuning ionic correlations in binary IL blends to provide pathways towards higher energy density capacitive interfaces. We show how the addition of surface-active amphiphilic anions weakens these correlations increasing the interfacial charge density and capacitance of these IL blends. Notably, we find that mixing surface-active amphiphilic anions with nonamphiphilic ILs doubles the capacitance at negative surfaces. We hypothesize that polarity-dictated anion-anion van der Waals interactions serve to weaken IL cation-anion interactions and ultimately drive molecular assembly at negative surfaces, increasing capacitance. I will also present our complementary investigations of non-amphiphilic binary IL mixtures and provide spectroscopic insight into bulk ion correlations within these systems. Our study ultimately paves the path towards fundamental investigations into the chemical nature of additives in ionic liquid blends to boost performance within next-generation supercapacitors.
Ionic Liquid and Plastic Crystal Battery Electrolytes Utilising New Cation and Anion Structures
Authors: Pringle Jenny , Vallana Federico , Azad Faezeh Makhlooghi , Sourjah Sithy M , Warrington Anna , Forsyth Maria
Published: December 2024

It is well known that the nature of the cations and anions used to make ionic liquid (IL) electrolytes can have a significant impact on their chemical and physical properties and on their performance in devices, for example when used in lithium or sodium batteries. The same is true for organic ionic plastic crystals (OIPCs); these salts are structurally analogous to ILs, but they are solid at room temperature and display dynamics that can allow their use as solid state electrolytes. However, the structure-property relationships are arguably even less well understood in OIPCs. Furthermore, the addition of different lithium or sodium salts to ILs and OIPCs, to enable their use in lithium or sodium batteries, introduces further complexities in terms of understanding and optimising the thermal, electrochemical and transport properties.

To advance the understanding and application of IL and OIPC-based electrolytes it is important to continue to design and investigate new cation and anion structures. For example, we have recently developed new families of IL and OIPC electrolytes using cations such as the hexamethylguanidinium, cyano- or ether-functionalised ammoniums, oxazolidiniums and morpholiniums, in combination with a range of fluorinated and non-fluorinated anions. Furthermore, a new and seldom explored family of materials can be created by tethering the cation and anion together to form zwitterions.

This presentation will give an overview of our recent work making new families of non-volatile electrolytes based on ILs, OIPCs and zwitterions and understanding the impact of structure on device performance. Highlights will include the excellent properties and performance imparted by small oxygen-containing cations, and the promising new results using more environmentally friendly, non-fluorinated salts for Li and Na batteries.

References

[1] A. Warrington, M. Hasanpoor, A. Balkis, P. C. Howlett, O. E. Hutt, M. Forsyth, J. M. Pringle, Energy Storage Materials 2023, 63, 102984

[2] A. Sourjah, C. S. M. Kang, C. M. Doherty, D. Acharya, L. A. O’Dell, J. M. Pringle, Phys. Chem. Chem. Phys., 2023, 25, 16469

[3] F. Makhlooghiazad, L. A. O’Dell, L. Porcarelli, C. Forsyth, N. Quazi, M. Asadi, O. Hutt, D. Mecerreyes, M. Forsyth, J. M. Pringle, Nat. Mater., 2022, 21, 228