Concentrated Electrolyte Solutions Research Articles

Kinetics of Macroion Adsorption on Silica: Complementary Theoretical and Experimental Investigations for Poly-l-arginine.

A comprehensive approach enabling a quantitative interpretation of poly-l-arginine (PARG) adsorption kinetics at solid/electrolyte interfaces was developed. The first step involved all-atom molecular dynamics (MD) modeling of physicochemical characteristics yielding PARG molecule conformations, its contour length, and the cross-section area. It was also shown that PARG molecules, even in concentrated electrolyte solutions (100 mM NaCl), assume a largely elongated shape with an aspect ratio of 36. Using the parameters derived from MD, the PARG adsorption kinetics at the silica/electrolyte interface was calculated using the random sequential adsorption approach. These predictions were validated by optical reflectometry measurements. It was confirmed that the molecules irreversibly adsorbed in the side-on orientation and their coverage agreed with the elongated shape of the PARG molecule predicted from the MD modeling. These theoretical and experimental results were used for the interpretation of the quartz crystal microbalance measurements carried out under various pH conditions. A comprehensive analysis unveiled that the results stemming from the hydrodynamic theory postulating a lubrication-like (soft) contact of the macroion molecules with the sensor adequately reflect the adsorption kinetics. The range of validity of the intuitively used Sauerbrey model was also estimated. It was argued that acquired results can be exploited to control macroion adsorption at solid/liquid interfaces. This is essential for the optimum preparation of their supporting layers used for bioparticle immobilization and shell formation at nanocapsules in targeted drug delivery.

Investigation of Influencing Factors on Power Generation Performance in Reverse Electrodialysis

The importance of meeting energy demands from renewable sources is growing daily. Reverse electrodialysis (RED) is a membrane-based technology that produces energy using electrolyte solutions with different salinities. This study has generated energy from the RED system using the commercial Fujifilm Type II ion exchange membranes (IEMs). Many parameters affect the power generation performance of the RED system. This study systematically investigated the parameters, the presence of divalent ions and organic molecules, the electrolyte solution concentration, and the flow velocity. The flow velocity results indicated that energy efficiency increased with increasing flow velocity of the electrolyte solutions. The presence of divalent ions created uphill transport. The results showed that increasing the mole ratio of divalent ions in the feed electrolyte solutions dramatically decreased the RED system performance due to increasing resistances. The organic fouling test of the anion exchange membranes (AEMs) was carried out using a real humic and fulvic acid mixture under static conditions. The results indicated that fouling layers formed in the AEMs structure, and these layers decreased by 30% of RED performance. Lastly, the RED system's long-term performance was tested for 4 hours at a constant current density of 8 A/m2 before and after AEM fouling experiments. The results revealed the fouling layers severely reduced the power generation performance of the RED system.

Beyond the Debye-Hückel limit: Toward a general theory for concentrated electrolytes.

The phenomenon of underscreening in concentrated electrolyte solutions leads to a larger decay length of the charge-charge correlation than the prediction of Debye-Hückel (DH) theory and has found a resurgence of both theoretical and experimental interest in the chemical physics community. To systematically understand and investigate this phenomenon in electrolytes requires a theory of concentrated electrolytes to describe charge-charge correlations beyond the DH theory. We review the theories of electrolytes that can transition from the DH limit to concentrations where charge correlations dominate, giving rise to underscreening and the associated Kirkwood Transitions (KTs). In this perspective, we provide a conceptual approach to a theoretical formulation of electrolyte solutions that exploits the competition between molecular-informed short-range (SR) and long-range interactions. We demonstrate that all deviations from the DH limit for real electrolyte solutions can be expressed through a single function ΣQ that can be determined both theoretically and numerically. Importantly, ΣQ can be directly related to the details of SR interactions and, therefore, can be used as a tool to understand how differences in representations of interaction can influence collective effects. The precise function form of ΣQ can be inferred through a Gaussian field theory of both the number and charge densities. The resulting formulation is validated by experiment and can accurately describe the collective phenomenon of screening in concentrated bulk electrolytes. Importantly, the Gaussian field theory predictions of the screening lengths appear to be less than ∼1nm at concentrations above KTs.

Electrostatic Aspect of the Proton Reactivity in Concentrated Electrolyte Solutions.

Water-in-salt electrolytes with a surprisingly large electrochemical stability window of ≤3 V have revived interest in aqueous electrolytes for rechargeable lithium-ion batteries. However, recent reports of acidic pH measured in concentrated electrolyte solutions appear to be in contradiction with the suppressed activity of the hydrogen evolution reaction (HER). Therefore, the fundamental thermodynamics of proton reactivity in concentrated electrolyte solutions remains elusive. In this work, we have used density functional theory-based molecular dynamics (MD) simulations and the proton insertion method to investigate how the HER potential shifts in concentrated LiCl solutions under both acidic and alkaline conditions. Our results show that the intrinsic HER activity increases significantly with the salt concentration under acidic conditions but remains relatively constant under alkaline conditions. Moreover, by leverage over finite-field MD simulations, it is found that a determining factor for the HER activity is the Poisson potential of the liquid phase, which increases in concentrated electrolyte solutions with comparable values from both density functional theory and point-charge models.

Anodic Dissolution Behavior of Si Electrode in HF Solution Containing H2O2

Silicon is expected to be as anode materials for lithium-ion batteries because the battery performance can be improved by increasing surface area1). Metal-assisted chemical etching (MACE) 2) is a low-cost method to form the nano-silicon structures on Si electrode, which is called silicon nanowires (SiNWs). Though this method enables the fabrication of SiNWs to increase the surface area on Si electrode, the mechanisms on MACE have not been clarified yet. This study aimed to investigate the anodic dissolution behavior of Si electrode to understand the effect of electrolyte concentrations on MACE by electrochemical methods in the HF solution containing H2O2.Electrochemical measurements were carried out by a three-electrode system. An electrochemical cell was made of a polypropylene (PP) to use HF as the electrolyte. The counter electrode was a platinum wire, and the reference electrode was a KCl-saturated Ag/AgCl electrode (SSE) fabricated by the polycarbonate that can be used in the HF solution. The Si, Ag, and Si with deposited Ag particles were used as working electrodes. The Si electrode was made from n-type silicon wafers with a (100) surface. The electrode of Si with deposited Ag particles was prepared using an electroless Ag plating. A mixture of HF and H2O2 was used as the electrolyte solution. To investigate MACE behavior, the measurements of the electrode potential, polarization curve, and electrochemical impedance were carried out at each electrode. The electrode potential of Si with deposited Ag particles was measured for arbitrary time in the electrolyte solution. The potentiostatic polarization of Si electrode was performed to investigate anodic dissolution behavior. The electrochemical impedance measurements were carried out with an AC potential amplitude of 10 mV at arbitrary DC potential. The frequency range was 100 kHz to 0.01 Hz at five frequencies per decade.In the electrolyte solution of HF containing H2O2, the electrode potential of the Si with deposited Ag particles shifted to the less noble potential at the initial stage during MACE regardless of the concentrations of electrolyte solution. The cathodic polarization curve of Ag indicated that the cathodic reactions on Ag electrode were affected by the H2O2 concentrations. The anodic polarization curve of Si electrode demonstrated that the dissolution and film formation may occur on Si electrode, which was depended on the HF concentrations. Based on these results, the electrochemical impedance measurement was performed on the Si electrode. The dissolution and oxide film formation as the anodic reactions and the reduction reactions as the cathodic reactions during MACE were discussed to determine the suitable conditions for fabrication of SiNWs on the Si electrode. References Haibin Li, Shinya Kato, Yosuke Ishii, Yasuyoshi Kurokawa and Tetsuo Soga, Nano Ex., 3, 045010 (2023).Ming-Liang Zhang et al, J. Phys. Chem. C, 112, 4444 (2008).

Improvement of LiNi0.8Co0.1Mn0.1O2 Positive-Electrode Properties by Introducing Fluorinated Propionic Acid Ester-Based Solvent to Highly Concentrated Lin(SO2F)2 Electrolyte Solutions

IntroductionFurther improvement in energy density and safety of lithium-ion batteries is required to expand the spread of EVs. A LiNi0.8Co0.1Mn0.1O2 (NCM811) positive-electrode is drawing attention because it can deliver a high discharge capacity of about 220 mAh g-1 or more by raising the charging upper limit potential to 4.6 V (vs. Li/Li+). In general, however, the electrolyte solution is oxidized and decomposed at about 4 V (vs. Li/Li+) or more, and cracks of the NCM811 particles occur, which results in a significant decrease in charge and discharge performance. Accordingly, highly concentrated electrolyte solutions are attracting attention because of their high stability against oxidation and thermal stability1, while the problem is that the viscosity is high and the ion conductivity is low.In this study, flame-retardant tris (2,2,2-trifluoroethyl) phosphate (TFEP)-based electrolyte solutions containing high concentrations of LiN(SO2F)2 (LiFSI) were prepared, and methyl 2,3,3,3-tetrafluoropropionate (4FMP) as a co-solvent and methyl perfluoropropionate (5FMP) as a diluent were introduced to reduce the viscosity and improve the ion conductivity. The charge-discharge characteristics of NCM811 positive-electrodes were investigated by conducting charge-discharge tests over 100 cycles in a voltage range of 3.0-4.6 V using a half-cell with an NCM811 working electrode and a lithium metal counter electrode.ExperimentalThe nearly saturated 2.2 M LiFSI/TFEP (TFEP/Li+=1.7 by mol) electrolyte solution, and the highly concentrated LiFSI/TFEP+4FMP (TFEP:4FMP=1:1 and 2:1 by vol.) and LiFSI/TFEP+5FMP (TFEP/Li+=1.7 by mol, TFEP:5FMP=1:1, 2:1 and 3:1 by vol.) electrolyte solutions were prepared. An NCM811 composite electrode (13 mmf) was used as a working electrode and a Li foil (14 mmf) was used as a counter electrode, and each electrolyte solution was used to prepare a Li|NCM811 cell. Charge-discharge tests were conducted between 3.0 and 4.6 V. The charge/discharge rate in the first cycle was set to C/10, which corresponds to a current that can theoretically complete each charge (discharge) process in 10 h under the presumption that the theoretical specific capacity of NCM811 is 278 mAh/g. In addition, the NCM811 working electrode after 100 cycles was washed with dimethyl carbonate, dried, and then analyzed by a field emission scanning electron microscope (FE-SEM)/energy dispersive X-ray spectroscopy (EDX). To evaluate the oxidation resistance of the electrolyte solutions, linear sweep voltammetry (LSV) was performed by using three-electrode cell having a Pt working electrode (12 mmf).Results and DiscussionFigure 1 shows the changes in discharge capacity of Li|NCM811 cells in 100 cycles. 2.1 M LiFSI/TFEP+4FMP (TFEP: 4FMP=2:1 by vol., (TFEP+4FMP)/Li+=2.3 by mol., 4FMP electrolyte) and 1.6 M LiFSI/TFEP+5FMP (TFEP: 5FMP=2:1 by vol., 5FMP-diluted electrolyte) showed the highest performance among the 4FMP- and 5FMP-diluted electrolyte solutions, respectively. After 100 cycles, the discharge capacity retention was 92.5% and 93.1% in the 4FMP- and 5FMP-diluted electrolytes, respectively. In addition, the average Coulomb efficiency reached 99.0% and 99.3%, respectively. The 4FMP electrolyte showed the highest discharge capacity in the 100th cycle (209.0 mAh/g), and the 5FMP-diluted electrolyte showed the highest discharge capacity retention and average Coulomb efficiency. After the 100 charge-discharge cycles, the F atomic concentrations on the surface of NCM811 were 11.6% and 10.1% in 4FMP- and 5FMP-diluted electrolytes, respectively, which was the lowest among the 4FMP and 5FMP-diluted electrolyte solutions. LSV of Pt showed a large anodic current due to the oxidative decomposition of the 4FMP electrolyte, suggesting that the charge-discharge performance of NCM811 is improved by forming a thin and uniform protective film on it. On the other hand, since the oxidation decomposition current of the 5FMP-diluted electrolyte was kept at the lowest level, the charge-discharge performance of NCM811 should be improved by the high stability against oxidation of the electrolyte solution. Figure 1

Probing Electrochemical Reactions at the Electrode-Electrolyte Interface in Lithium Metal Battery, Combining Experimental Approach and Computational Calculation

Lithium-ion batteries have attracted significant attention for applications such as energy supply for electric vehicles, large-scale stationary power sources, and energy storage for renewable energy. Research and development of various electrode materials continue for further increasing charge / discharge capacity, expanding operation lifetime. Theoretical capacity of lithium metal is 3860 mAh/g, which is approximately 10 times larger than that of graphite negative electrode (372 mAh/g), which is commonly used in conventional lithium-ion batteries. Therefore, lithium metal batteries, which combine lithium metal negative electrode with a commonly used Lithium nickel manganese cobalt oxides (NCM) positive electrode, are expected to significantly increase energy density and considered to be one of the promising next-generation batteries. Improving the performance of the electrolyte solution is essential to fully utilize the newly developed electrode materials for both positive and negative electrodes. As lithium metal exhibits the most negative potential (-3.04 V v.s. SHE), the electrolyte solution must possess high reduction stability. At the same time, passivation film, solid electrolyte interface (SEI), formed on lithium metal also plays an important role to prevent further decomposition of electrolyte solution. Meanwhile, positive electrodes have oxidation potentials of 4.2 V or higher, and the reactivity at the positive electrode (cathode) and the electrolyte interface (CEI) is also a crucial factor influencing the performance of lithium metal batteries. Thus, controlling the reactions of the electrolyte solution at the electrode interface is a critical factor for operating lithium metal batteries stably and reliably over the long term.In recent years, research and development of electrolyte solutions have focused on enhancing reduction and oxidation stability by exploring various types of solvents, electrolyte salts, and controlling their concentrations. Ether-based electrolyte solutions are known for their higher reduction stability comparing commercially available carbonate-based electrolyte solutions. However, the oxidative stability of conventional concentration ether-based electrolyte solution is quite low, leading the decomposition at oxidation potentials over 4 V. Strategies to improve the oxidative stability of ether-based electrolyte solutions have been extensively studied, and one of the candidates is increasing electrolyte salt concentration.In this study, we have conducted electrochemical performance tests on lithium metal batteries using a concentrated electrolyte solution of ether-based solvents and LiFSI (Lithium bis(trifluoromethanesulfonyl)imide), with lithium metal and NCM positive electrode. As the solvation structures in the electrolyte solution directly affect the formation mechanism of SEI and CEI, the solvation structures are estimated by Raman spectroscopy, and their chemical stability and decomposition mechanisms are estimated by DFT calculations. We have conducted detailed analyses of reduction and oxidative decomposition reactions occurring at the electrode surface, and confirmed the applicability of the prediction combining Raman spectroscopy and DFT calculation. Figure 1

Nano-structured and High-performance Mn-based Positive Electrode Materials for Lithium-ion Batteries

Towards widespread adoption of electric vehicles, Co/Ni-free and high energy density positive electrode materials for lithium-ion batteries are necessary. Among the various positive electrode materials, stoichiometric “zigzag”-type layered LiMnO2 with orthorhombic space-group symmetry has been extensively studied as potential high-energy and low-cost positive electrode materials. Although orthorhombic LiMnO2 delivers a large reversible capacity of over 200 mA h g-1 thorough a phase transition from layered to spinel-like phase during charging and discharging, over 30 cycles are required to obtain such a large reversible capacity due to the sluggish phase transition kinetics. In this study, nanostructured LiMnO2 with both orthorhombic and monoclinic layered domains is synthesized, and its electrochemical performance as positive electrode materials is examined. The nanostructured LiMnO2 delivers a maximum reversible capacity of >200 mA h g-1 within 5 cycles, indicating that the phase transition kinetics to the spinel-like phase upon electrochemical cycling are faster when compared with orthorhombic LiMnO2. Moreover, a significant improvement of cycle performance, i.e., ~90% retention after 100 cycles, is achieved by using a highly concentrated electrolyte solution coupled with lithium phosphate coating through suppression of Mn dissolution into electrolyte. From these results, the feasibility of practical Co/Ni-free high-energy positive electrode materials will be discussed in detail.

Corrosion Inhibition of Stainless Steel in Highly Concentrated Lin(SO2F)2 Electrolyte Solutions with Organophosphate Esters

Introduction To improve the energy density of lithium-ion batteries, various kinds of electrode materials have been developed. Silicon and lithium metal are considered promising as novel high-capacity negative-electrode materials, while the practical use of them is limited due to the significant morphological changes during charging and discharging. Lithium bis(fluorosulfonyl)imide (LiFSI) has been attracting attention as an alternative salt to LiPF6 as it formed a superior solid electrolyte interphase (SEI) on the negative electrodes. However, LiFSI-based electrolyte solutions cause corrosion of cell components at high voltages; i.e., an aluminum current collector (Al) (>3.7 V)[1] and a stainless steel (SS) case used in cylindrical and coin cells (>3.8 V)[2]. In general, SS corrodes more severely than Al. The SS corrosion can be inhibited in the highly concentrated electrolyte solutions.[2] However, to our best knowledge, there are no reports on the additives and solvents that can effectively inhibit the corrosion. In this study, we focused on organophosphate ester solvents, and investigated effects of LiFSI concentration on the inhibition of SS corrosion. Experimental The highly concentrated electrolyte solutions used were 3.8 M LiFSI dissolved in triethyl phosphate (TEP) (TEP/Li=0.95 by mol., TEP electrolyte), and 2.2 M LiFSI dissolved in tris(2,2,2-trifluoroethyl) phosphate (TFEP) (TFEP/Li=1.7 by mol., TFEP electrolyte). 6 M LiFSI dissolved in dimethyl carbonate (DMC) (DMC/Li=1.1 by mol., DMC electrolyte) was also used as a reference. The corrosion behaver of SS electrodes was examined by cyclic voltammetry (CV) for 100 cycles in a voltage range of 3.0-4.6 V (vs. Li/Li+) using a three-electrode cell, with a SUS316L (SS316) working electrode, and lithium metal as both the counter and reference electrodes. The electrode surface after CV was observed by an optical microscope. Result and Discussion Figure 1 shows cyclic voltammograms (CVs) of SS316 electrodes in each electrolyte solution. In DMC electrolyte, an anodic current due to the corrosion was clearly observed in the 10th cycle at ca. 4.1-4.2 V (vs. Li/Li+), and further increased in subsequent cycles, indicating the progression of SS corrosion. In contrast, such a corrosion current peak in TEP electrolyte significantly reduced to less than one-tenth (<1.5 μA cm-2) compared to the DMC electrolyte. Moreover, no corrosion peak was observed in TFEP electrolyte. After 100 cycles in the DMC electrolyte, a number of corrosion pits and widespread corrosion products were observed, as shown in Figure 2. Similarly, corrosion pits were observed for the TEP electrolyte, while no corrosion products were seen. In contrast, neither corrosion pits nor corrosion products were obvious in the TFEP electrolyte. These results indicate that the organophosphate esters, TEP and TFEP, can effectively inhibit the corrosion of SS. More detailed analysis of the SS surface film was conducted through X-ray photoelectron spectroscopy. We will discuss how it contribute to the corrosion inhibition in our presentation. Reference [1] E. Svensson et al., J. Phys. Chem. C, 127, 7921-7928 (2023).[2] C. Luo et al., Electrochem Acta., 419, 140353 (2022). Figure 1

Energy-conversion efficiency for producing oxy-hydrogen gas using a simple generator based on water electrolysis

Producing hydrogen efficiently through water electrolysis could greatly reduce fossil fuel consumption. As well as this renewable energy source will also help combat global warming and boost economic investment opportunities. This paper studied some factors affecting the performance of oxy-hydrogen/hydroxy (HHO) gas generator, such as applied voltage (from 10.5 to 13.0 V) and electrolyte solution concentration (from 0.05 to 0.20 M), using a dry fuel cell based on the electrolyzing technique of water. The results revealed that the HHO gas production rate, power consumption, and temperature change of electrolyte solution increased significantly with increasing the tested applied voltage and electrolyte concentration. This study concluded that the optimum conditions for producing HHO gas ranged from 11.5 to 12.0 V for applied voltage and from 0.05 to 0.10 M for KOH concentration according to the lowest specific energy and highest HHO gas generator efficiency. Under the previous optimum conditions, the highest productivity, specific energy, and efficiency of the HHO gas generator were 343.9 cm3 min−1, 3.43 kW h m−3, and 53.79%, respectively, using 12.0 V for applied voltage and 0.10 M for electrolyte solution concentration. These findings provide an unambiguous direction for adjusting the operational factors (applied voltage and electrolyte concentration) for efficient HHO gas production and use in different applications. Furthermore, the required energy to operate the HHO gas generator can be obtained from renewable sources.

Antioxidant Activity of Asphaltene and Resinous Components in the Magnetic Field

Using the voltammetric method of oxygen electroreduction, an analysis of the antioxidant activity of resin-asphaltene components isolated from 2 crude oils of different compositions before and after exposure to a magnetic field was carried out. For the studied asphaltenes, weakly polar and polar resins, an increase or decrease in antioxidant activity is observed with increasing sample concentration in the background electrolyte solution. Petroleum antioxidants are part of a complex colloidal structural system and are associated with it by associative interactions that arise as a result of changes in the size and activity of associates of the petroleum system as a whole.

Experimental study on the preparation of superalloy Inconel718 heat exchanger channels by electrochemical etching method

The nuclear energy field requires the construction of heat exchangers that can withstand sufficiently high temperatures. In this paper, the etching technique was utilized to fabricate heat exchange channels on Inconel718 plates, and experiments were carried out in NaCl-ethylene glycol solution, three temperature conditions of 35 °C, 40 °C, and 45 °C, and two concentrations of electrolyte solutions, 0.5 mol/L and 1 mol/L, with the addition of 50 kHz ultrasound for comparison. The experimental results show that the etching rate can be as high as 2.894 mm/h, and the inter-electrode current is as high as 908 mA. The roughness characterization of the etching channel Ra and Rq measured by the aspheric surface measuring instrument can be as low as 2.416 μm and 2.647 μm, respectively. In the images generated by SEM scanning, it is found that uneven distribution of pits and bumps exist in the etching channel, but their diameters are all less than 0.1 μm, which means the etched channel is acceptably smooth.

Development of a consistent geochemical model of the Mg(OH)2–MgCl2–H2O system from 25°C to 120°C

The formation of magnesium chloride-hydroxide salts (magnesium hydroxychlorides) has implications for many geochemical processes and technical applications. For this reason, a thermodynamic database for evaluating the Mg(OH)2–MgCl2–H2O ternary system from 0 °C–120 °C has been developed based on extensive experimental solubility data. Internally consistent sets of standard thermodynamic parameters (ΔGf°, ΔHf°, S°, and CP) were derived for several solid phases: 3 Mg(OH)2:MgCl2:8H2O, 9 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2: 2H2O(s), brucite (Mg(OH)2), bischofite (MgCl2:6H2O), and MgCl2:4H2O. First, estimated values for the thermodynamic parameters were derived using a component addition method. These parameters were combined with standard thermodynamic data for Mg2+(aq) consistent with CODATA (Cox et al., 1989) to generate temperature-dependent Gibbs energies for the dissolution reactions of the solid phases. These data, in combination with values for MgOH+(aq) updated to be consistent with Mg2+-CODATA, were used to compute equilibrium constants and incorporated into a Pitzer thermodynamic database for concentrated electrolyte solutions. Phase solubility diagrams were constructed as a function of temperature and magnesium chloride concentration for comparisons with available experimental data. To improve the fits to the experimental data, reaction equilibrium constants for the Mg-bearing mineral phases, the binary Pitzer parameters for the MgOH+ — Cl− interaction, and the temperature-dependent coefficients for those Pitzer parameters were constrained by experimental phase boundaries and to match phase solubilities. These parameter adjustments resulted in an updated set of standard thermodynamic data and associated temperature-dependent functions. The resulting database has direct applications to investigations of magnesia cement formation and leaching, chemical barrier interactions related to disposition of heat-generating nuclear waste, and evaluation of magnesium-rich salt and brine stabilities at elevated temperatures.

Unlocking Electrode Performance of Disordered Rocksalt Oxides Through Structural Defect Engineering and Surface Stabilization with Concentrated Electrolyte

Abstract Li‐excess cation‐disordered rocksalt oxides can boost the energy density of rechargeable batteries by using anionic redox, but the inferior reversibility of anionic redox hinders its use for practical applications. Herein, a binary system of Li3NbO4–LiMnO2 is targeted and the systematic study on factors affecting electrode reversibility, i.e., percolation probability, electronic conductivity, defect concentrations, and electrolyte solutions, is conducted. A Mn‐rich sample, Li1.1Nb0.1Mn0.8O2, delivers a smaller reversible capacity compared with a Li‐rich sample, Li1.3Nb0.3Mn0.4O2, because of the limitation of ionic migration associated with insufficient percolation probability for disordered oxides. Nevertheless, a larger reversible capacity of Li1.3Nb0.3Mn0.4O2 originates from excessive activation of anionic redox, leading to the degradation of electrode reversibility. The superior performance of Li1.1Nb0.1Mn0.8O2, including Li ion migration kinetics and electronic transport properties, is unlocked by the enrichment of structural defects for nanosized oxides. Moreover, electrode reversibility is further improved by using a highly concentrated electrolyte solution with LiN(SO2F)2 through the surface stabilization on high‐voltage exposure. Superior capacity retention, &gt;100 cycles, is achieved for nanosized Li1.1Nb0.1Mn0.8O2. The electrolyte decomposition and surface stabilization mechanisms are also carefully examined, and it is revealed that the use of highly concentrated electrolyte solution can effectively prevent lattice oxygen being further oxidized and transition metal ion dissolution.

Giant Thermoelectric Response of Confined Electrolytes with Thermally Activated Charge Carrier Generation.

The thermoelectric response of thermally activated electrolytes (TAEs) in a slit channel is studied theoretically and by numerical simulations. The term TAE refers to electrolytes whose charge carrier concentration is a function of temperature, as recently suggested for ionic liquids and highly concentrated aqueous electrolyte solutions. Two competing mechanisms driving charge transport by temperature gradients are identified. For suitable values of the activation energy that governs the generation of charge carriers, a giant thermoelectric response is found, which could help explain recent experimental results for nanoporous media infiltrated with TAEs.

Unified understanding and mitigation of detrimental phase transition in cobalt-free LiNiO2

Ni-enriched layered materials are used as electrode materials of Li-ion batteries for electric vehicle applications. Stoichiometric LiNiO2 with cationic Ni3+/Ni4+ redox is the ideal electrode material, but the gradual loss of capacity at the high voltage region, associated with Ni ion migration, hinders its use for practical applications. Therefore, to improve electrode reversibility of LiNiO2, less abundant Co ions and/or other electrochemically inactive ions, e.g., Al3+ ions, are in part substituted for Ni ions. Nevertheless, a unified understanding of improvement by metal substitution is as yet not established. In this study, the origin causing detrimental phase transition in LiNiO2 is discussed through the detailed analysis on LiNiO2 integrated with nanosized Li3PO4 derived from a metastable and rocksalt LiNiO2–Li3PO4 solid solution sample. LiNiO2 derived from the metastable rocksalt oxide has approximately 6 % anti-site defects, and the particle size growth is suppressed by uniformly dispersed nanosized Li3PO4. In low crystallinity LiNiO2 with partial structural disordering, the Ni ion migration to tetrahedral sites is effectively suppressed because of repulsive electrostatic interaction from Ni ions in Li layers. Moreover, from these findings, non-stoichiometric Li0.975Ni1.025O2 with smaller particle size has been directly synthesized without high-energy milling and Li3PO4 integration, and significant improvement of electrode reversibility is achieved. Electrode reversibility of non-stoichiometric Li0.975Ni1.025O2 is further improved through surface stabilization in a highly concentrated electrolyte solution. The unified understanding of deterioration mechanisms for LiNiO2 offers a new criterion to design Co-free LiNiO2 without metal substitution, leading to full utilization of a reversible capacity for layered materials.

Transformations in crystals of DNA-functionalized nanoparticles by electrolytes.

Colloidal crystals have applications in water treatments, including water purification and desalination technologies. It is, therefore, important to understand the interactions between colloids as a function of electrolyte concentration. We study the assembly of DNA-grafted gold nanoparticles immersed in concentrated electrolyte solutions. Increasing the concentration of divalent Ca2+ ions leads to the condensation of nanoparticles into face-centered-cubic (FCC) crystals at low electrolyte concentrations. As the electrolyte concentration increases, the system undergoes a phase change to body-centered-cubic (BCC) crystals. This phase change occurs as the interparticle distance decreases. Molecular dynamics analysis suggests that the interparticle interactions change from strongly repulsive to short-range attractive as the divalent-electrolyte concentration increases. A thermodynamic analysis suggests that increasing the salt concentration leads to significant dehydration of the nanoparticle environment. We conjecture that the intercolloid attractive interactions and dehydrated states favour the BCC structure. Our results gain insight into salting out of colloids such as proteins as the concentration of salt increases in the solution.

Electrical conductivity of heterogeneous ion exchange membranes in solutions of mono-, di- and tricarboxylic acids and its effect on the process of electrodialysis of solutions containing organic acids

In this study, the electrical conductivity of cation-exchange and anion-exchange membranes was studied in solutions containing both strong (sodium chloride and acetate) and weak (acetic, succinic and citric acids) electrolytes. The results obtained indicate that the concentration dependence of the electrical conductivity of membranes in weak electrolytes differs significantly from that observed for solutions of strong electrolytes. In the case of an acetic acid solution, the electrical conductivity of the membranes is higher than that of the equilibrium solution over the entire range of concentrations that were studied. It has been shown that existing models of the transport and structural organization of membranes allows describing the structural parameters of ion-exchange membranes in contact with strong electrolytes. In sodium chloride and sodium acetate solutions, the obtained dependences were processed within the framework of microheterogeneous and three-wire models to establish the influence of the nature of the electrolyte on the transport and structural characteristics of the membranes. The dependence of electrical conductivity on the concentration of a weak electrolyte solution does not allow the use of either microheterogeneous or extended three-wire models for the description of the structure-property relationship of ion-exchange materials. It has been shown that in acetic acid and partially succinic acid solutions, the solution provides the main contribution to the resistance of the electromembrane system. Based on the results obtained from measuring electrical conductivity, changes in the design of a laboratory electrodialyzer were proposed and experiments were carried out on desalting a solution of acetic acid. It has been shown that the use of thinner intermembrane separators in the desalting chamber leads to an increase in the integral current efficiency (from 0.32 to 0.44 at 0.6 A/dm2 and the same degree of desalination) and a reduction in specific energy consumption (from 3.0 to 1.9 kWh/mol at 0.6 A/dm2) during desalination of acetic acid. The results obtained can be further used to improve the parameters of the process of obtaining weak acids by bipolar electrodialysis.

Development of Durable Large-Sized CO2 Electrolysis Cells for Industrial Applications

Utilization of carbon dioxide (CO2) as a feedstock of valuable chemicals is necessary to achieve carbon neutrality. Toshiba is developing the low-temperature zero-gap type CO2 electrolysis cells to produce carbon monoxide (CO) [1,2]. CO can further be converted into various chemicals and fuels by catalytic reactions with hydrogen. To make the CO2 electrolysis technology industrially feasible, it is necessary to establish high-throughput system by expanding the electrode area and stacking the cells. Large-sized cells and stacks often suffer from low Faradaic efficiency for the CO production, which is related to insufficient and nonuniform supply of reactant CO2 gas to the cathode reaction sites. This time we focused on the development of large-sized single cells and fabricated an electrolysis cell with 400 cm2 electrodes. With properly designed gas flow plates and gaskets, the cell voltage and the CO Faradaic efficiency of the fabricated cell at a current density of 400 mA cm-2 were comparable to those of the previously developed smaller cells with 4 cm2 electrodes. The CO concentration in the cathode outlet gas reached ca. 80% by controlling the inlet CO2 flow rate. Stability is another essential property of CO2 electrolysis cells required for the industrial application. Cathode flooding and salt precipitation are major stability issues characteristic of relatively short-term operations, whose detailed mechanism is still in debate [3]. To mitigate those stability issues, we focused on the cathode inlet humidity and the pressure difference between the cathode and the anode. The former is related to the salt concentration in electrolyte solution around the cathode reaction sites, and the latter is related to the convection of electrolyte from the anode side to the cathode side. By controlling those parameters, stable performance over 100 h was achieved.Part of this work was commissioned by Ministry of the Environment, Government of Japan.[1] Y. Kofuji, A. Ono, Y. Sugano, A. Motoshige, Y. Kudo, M. Yamagiwa, J. Tamura, S. Mikoshiba, and R. Kitagawa, Chem. Lett., 50, 482-484 (2021).[2] Y. Kiyota, Y. Kofuji, A. Ono, S. Mikoshiba, and R. Kitagawa, 242nd ECS Meeting, I05-1942 (2022).[3] M. Sassenburg, M. Kelly, S. Subramanian, W. A. Smith, and T. Burdyny, ACS Energy Lett., 8, 321-331 (2023).

Spectroscopic and Computational Evaluation of Electrochemical Stability of Electrolyte Solutions; Solvents, Electrolytes and Their Concentration Dependence

Since the introduction of Lithium-ion batteries (LIBs) into commercial use, great improvements have been achieved in their performance such as energy density, durability, and safety. However, there still remain many technical issues to meet the increasing demands for a longer driving range of electric vehicles, a larger storage for renewable energy. Research and development of electrode active materials are extensively progressing to respond those market needs, and R&D for electrolyte solutions are also active in order to utilize the fullest extent of the newly developed electrode materials.Various kinds of characteristics are required for electrolyte solutions in LIBs. Ideally, the electrochemical stability in a wide potential range is needed, but almost all the electrolyte solutions reductively decompose on negative electrodes, and the decomposition products precipitate on the electrode to form a protective surface film, which is referred to as SEI (solid electrolyte interphase). Because the nature of SEI is influenced by chemical structures of electrolyte solutions, the solvents and lithium salts need to be combined properly to realize LIBs with better performance. Although the conventional electrolyte solutions show satisfactory performance to some extent, there still remain some disadvantages; instability against moisture and temperature, and volatility and flammability of carbonate ester solvents. Great efforts have been made to overcome those disadvantages in the conventional electrolyte solutions, for example, utilization of ionic liquid, polymer electrolytes and inorganic solid state electrolytes, and recently, highly concentrated electrolyte solution gathers a lot of attention.Based on these background, solid electrolyte interphase (SEI) formed on graphite in conventional and highly concentrated electrolyte solutions was thoroughly characterized by a combined experimental and computational study. The comprehensive understanding revealed that a chemical composition of SEI, as well as the solvation structures unstable to reductive potential, can be predicted by a profound understanding of density functional theory (DFT) calculation results of the solvates containing a counter anion. The solvation structures were determined by Raman spectroscopy to evaluate electron affinity (EA) and LUMO of the solvates containing an anion by DFT calculation. The chemical composition of SEI was quantitatively analyzed by X-ray photoelectron spectroscopy (XPS), and the results were compared with a prediction based on the calculation. The formation mechanism of SEI during charge and discharge process can be partly estimated by the combination of experiment and theoretical calculation. These results indicate that electrolyte solutions can be efficiently designed by predicting the physicochemical properties of SEI through the more effective utilization of DFT calculation. Thus, a combination of DFT prediction and experimental analysis is proved to be an effective approach to reveal SEI formation mechanisms, and can be utilized as a versatile approach to develop new solvents, electrolyte salts, and additives, and to design electrolyte solutions with appropriate concentration.It is expected that the oxidative stability and reaction mechanism of electrolyte solutions at the positive electrode can be estimated using similar approaches. Here, it is necessary to predict oxidative stability using ionization potentials (IP), rather than EA. In the same way, other solvents than carbonate, such as ethers and sulfones, which have been difficult to put into practical use in conventional electrolytes, can also be the target to be studied. By analyzing the solvation structure and estimating its chemical stability, we believe it will be possible to get many insights on the reactions that proceed at the interface between the electrode and the electrolyte. Figure 1