Organic Electrolyte Research Articles

Reinforcing an interfacial molecular dam through a multifunctional organic electrolyte additive for stable Zn anodes

Triazole obstructs water induced corrosion and modulates Zn ion flux through its hydrophobic and zincophilic properties.

Structural, morphological, electrical, and dielectric properties of Na2Cu5(Si2O7)2 for ASSIBs.

Solid inorganic electrolyte materials are fundamental components for constructing all-solid-state sodium-ion batteries. These solid electrolytes offer considerable benefits related to safety, electrochemical performance, and mechanical stability in comparison to liquid organic electrolyte systems. This study investigates the sodium ion conduction mechanism and relaxation kinetics in the sorosilicate material Na2Cu5(Si2O7)2, a potential solid electrolyte, using impedance spectroscopy. Analysis of the DC conductivity data demonstrates that sodium ion mobility follows Arrhenius behavior with a thermal activation energy barrier of 1.21 eV. This work highlights the importance of carefully choosing an appropriate equivalent circuit model to extract DC conductivity parameters from impedance data, given the contributions from both grain and grain boundary effects. Analysis of the AC conductivity and dielectric constant as a function of frequency and temperature demonstrates that ionic conduction takes place in this material through a process in which charge carriers overcome correlated energy barriers, known as correlated barrier hopping. The neutron diffraction patterns were analyzed using soft bond valence sum (BVS) techniques to map the possible ionic conduction pathways within the unit cell. Examination of the data points to obstructions in the sodium ion diffusion routes along the a-axis and diagonal of the bc plane within the triclinic unit cell. These bottlenecks likely contribute to the high activation energy and correspondingly low ionic conductivity observed. Analysis of dielectric properties by modulus verified that the ionic conduction relaxation phenomena exhibit thermal activation and a distribution of relaxation times. In summary, this work elucidates the microscopic ionic conduction mechanism in Na2Cu5(Si2O7)2 through extensive analysis encompassing DC/AC conductivity, electric modulus, and dielectric constant measurements. The insights gained into the ionic conduction mechanism will aid in engineering optimized ionic conductor materials for battery technologies.

Speciation of the proton in water-in-salt electrolytes.

Water-in-salt (WiS) electrolytes are promising systems for a variety of energy storage devices. Indeed, they represent a great alternative to conventional organic electrolytes thanks to their environmental friendliness, non-flammability, and good electrochemical stability. Understanding the behaviour of such systems and their local organisation is a key direction for their rational design and successful implementation at the industrial scale. In the present paper, we focus our investigation on the 21 m bis(trifluoromethanesulfonyl)imide (LiTFSI) WiS electrolyte, recently reported to have acidic pH values. We explore the speciation of an excess proton in this system and its dependence on the initial local environment using ab initio molecular dynamics simulations. In particular, we observe the formation of HTFSI acid in the WiS system, known to act as a superacid in water. This acid is stabilised in the WiS solution for several picoseconds thanks to the formation of a complex with water molecules and a neighboring TFSI- anion. We further investigate how the excess proton affects the microstructure of WiS, in particular, the recently observed oligomerisation of lithium cations, and we report possible notable perturbations of the lithium nanochain organisation. These two phenomena are particularly important when considering WiS as electrolytes in batteries and supercapacitors, and our results contribute to the comprehension of these systems at the molecular level.

Electrochemical reactivity and passivation of organic electrolytes at spinel MgCrMnO4 cathode interfaces for rechargeable high voltage magnesium-ion batteries

Contact ion pairs determine oxidative stability and interface layer formation.

The problems with solid-state sodium ion battery electrolytes and their solutions

In the context of the continuous growth of global demand for energy storage, electrochemical energy storage systems stand out among many energy storage technologies due to their excellent performance. At present, batteries as one of the most mainstream forms of electrochemical energy storage, such as fuel cells, lithium-ion batteries, and solid-state batteries, have been widely used. In particular, as the safety hazards existing in lithium-ion batteries due to the inclusion of organic electrolytes have gradually been recognized, solid-state batteries have received extensive attention and in-depth research for their higher safety performance. As an emerging electrochemical energy storage device, the most prominent feature of solid sodium-ion batteries is that they use solid electrolytes instead of traditional liquid electrolytes, which greatly improves the safety of batteries theoretically. Unfortunately, while solid electrolytes exhibit excellent chemical stability and good electrochemical performance, they still face a number of challenges in practical applications, including low ionic conductivity, poor interface contact, and short life span. In this paper, the characteristics, challenges, and solutions of electrolytes in solid-state sodium-ion batteries are discussed.

Conjugated polymer electrodes fabricated using rylene-based acceptors toward high energy and power density symmetric supercapacitors operable in an organic electrolyte environment

Conjugated polymer electrodes based on perylene diimide (PDI)–benzothiadiazole (BT) for symmetric supercapacitor device.

Development of a new electrodeposited AgSbS2/FTO electrode: Comparison of supercapacitance in Li-based aqueous and organic electrolytes

AgSbS2, or "miargyrite" material, could be a viable option for high-storage-capacity electrodes, guaranteeing exceptional performance. This document describes the production of AgSbS2/FTO thin films by the co-electrodeposition technique on Fluorine-doped-Tin-Oxide (FTO). To optimize the amount of silver, the films were deposited at a single potential −1.28/SCE, by varying [Ag+] between 0.01 and 0.03 M in aqueous conditions. Structurally, XRD-RAMAN analyses confirmed the formation of AgSbS2 thin films with cubic poly-crystallization. After elaboration, the thin films were analyzed morphologically, optically and electrochemically to better define their physico-chemical performances. This study proved through comparison that the co-electrodeposited AgSbS2/FTO electrode behaves as a pseudo-capacitor in aqueous and organic media based on LiOH (1 M) dissolved in water and acetonitrile within potential windows of [-0.9, 0 V] and [-0.8, 0.4 V]/SCE respectively. More precisely, using cyclical voltammetry (CV) analysis, the comparison revealed that the AgSbS2/FTO electrode presented a maximum specific capacity of about 1278 F/g in LiOH-water and 706 F/g in LiOH-acetonitrile. Finally, during the galvanostatic charge-discharge test, an 18 % and 4 % decrease in specific rate capacity was estimated as current density increased in LiOH-water and LiOH-acetonitrile respectively.

Strain induced electrochemical behaviors of ionic liquid electrolytes in an electrochemical double layer capacitor: Insights from molecular dynamics simulations.

Electrochemical Double Layer Capacitors (EDLCs) with ionic liquid electrolytes outperform conventional ones using aqueous and organic electrolytes in energy density and safety. However, understanding the electrochemical behaviors of ionic liquid electrolytes under compressive/tensile strain is essential for the design of flexible EDLCs as well as normal EDLCs, which are subject to external forces during assembly. Despite many experimental studies, the compression/stretching effects on the performance of ionic liquid EDLCs remain inconclusive and controversial. In addition, there is hardly any evidence of prior theoretical work done in this area, which makes the literature on this topic scarce. Herein, for the first time, we developed an atomistic model to study the processes underlying the electrochemical behaviors of ionic liquids in an EDLC under strain. Constant potential non-equilibrium molecular dynamics simulations are conducted for EMIM BF4 placed between two graphene walls as electrodes. Compared to zero strain, low compression of the EDLC resulted in compromised performance as the electrode charge density dropped by 29%, and the performance reduction deteriorated significantly with a further increase in compression. In contrast, stretching is found to enhance the performance by increasing the charge storage in the electrodes by 7%. The performance changes with compression and stretching are due to changes in the double-layer structure. In addition, an increase in the value of the applied potential during the application of strain leads to capacity retention with compression revealed by the newly performed simulations.

Secondary High-Temperature Treatment of Porous Carbons for High-Performance Supercapacitors

Supercapacitors are extensively used in urban rail transit, electric vehicles, renewable energy storage, electronic products, and the military industry due to its long cycle life and high power density. Porous carbon materials are regarded as promising anode materials for supercapacitors due to their high specific surface areas and well-developed pore structures. However, the over-developed pore structure often results in poor conductivity and reduced cycle stability due to the destruction of a carbon skeleton. Herein, we introduce an advanced strategy for preparing porous carbon with high specific surface areas (3333 m2 g−1), high electrical conductivity (68.6 S m−1), and fast ion transport channels through secondary high-temperature carbonization treatment. As a result, the fabricated porous carbon anode delivers a high specific capacitance (199.2 F g−1 at 1 A g−1) and outstanding rate performance (136.3 F g−1 at 20 A g−1) in organic electrolyte. Furthermore, the assembled symmetrical supercapacitor achieves an energy density of 43.2 Wh kg−1 at 625.0 W kg−1, highlighting the potential of a secondary high-temperature carbonization strategy in practical applications.

Evolution of Phases at the Surface and Interface of Mn Based Spinel Cathode with Coating Layer - a Spectroscopic Investigation

Surface modifications, commonly termed coatings or artificial interphases, are known to mitigate secondary reactions of charged cathodes with organic electrolyte and limit surface reconstruction. As a result, better electrochemical stability has been observed for coated cathodes in both liquid and solid electrolyte-based Li ion batteries (LIBs). However, these coatings, in contact with electrolyte, can be dynamic and evolve during processing stages or electrochemical cycling.In this work we investigate the interphases between spinel cathodes and two coating layers, LiNbO3 and Al2O3. The spinel LiMn2O4 (LMO) cathode and its doped variant LiMn1.5Ni0.5O4 (LMNO), owing to their three-dimensional structure, have high-rate and high-power capability with moderate energy density. With conventional electrolytes, the surface transition metal undergoes reduction forming thin binary or layered ternary oxides when charged beyond 4.2V (vs Li), restricting Li ion transport, and thereby compromising accessible capacity. This along with dissolution of manganese by HF (generated at the liquid electrolyte-electrode interface) restricts long-term applicability in practical LIBs thus necessitating surface coating or doping. In our experiments we choose epitaxial thin-film cathodes and thin-film coating materials. These provide large interface, and hence interphase areas, of well-defined crystal orientation, facilitating characterisation to deepen our understanding of the surface reactions occurring. We form an epitaxial film of cathode material using pulsed laser deposition (PLD) followed by controlled deposition of Al2O3 via atomic layer deposition (ALD) or LiNbO3 via PLD.We will present the detailed characterisation analysis of coated and uncoated spinel thin films. The epitaxial nature and crystal structure of deposited thin films are confirmed using thin film X-ray diffraction. Structurally, the phase diagram of Li-Mn(Ni)-O is complicated with many possible crystal structures with varying lithium content as well as different oxidation states of manganese. Hence, we employ a combination of X-ray absorption and photoelectron spectroscopies (XAS/XPS) to look at the chemical states of Mn ion in the cathode and Nb and Al ions in LiNbO3 and Al2O3 coating layers. For the as deposited fresh samples, the effect of deposition conditions is evaluated using XAS of the Mn L-edge and Al K-edge. XPS depth profiles of elemental distribution in the thin film heterostructures are obtained at three different incident X-ray energies (up to 6.6 kV) – thus providing chemical information from the surface, coating and at the interface of coating and cathode layers. Subsequently we electrochemically cycled these films in organic electrolyte against Li metal anode and further spectroscopic investigations were carried out. The effect of Al2O3 vs LiNbO3 coatings on retaining the structure of cathode material is probed and we will discuss the understanding thereby developed.

New Low Cost Sulfide Electrolytes for All Solid State Batteries

The low cost, safe and high energy storage technology is needed to ensure a continuous energy supply from renewal energy sources. However, current Li-ion batteries (LiBs) are facing challenges to fulfil the safety and high energy and power demands of fast-growing market of electric vehicles (EVs). In particular, liquid organic electrolytes used in conventional LIBs have raised the safety issues due to serious fire risk. Solid state batteries (SSBs) are considered to provide better safety as compared to LIBs because of solid electrolytes (SEs) are used in SSBs instead of flammable organic liquid based electrolytes [1-4].The various types of solid electrolytes have already been reported for SSBs which can be divided into oxides, sulfides, halides and polymers based on their properties, advantages and disadvantages [5]. Among these solid electrolytes, sulfide solid electrolytes have advantages over other due to high conductivity and ductile nature of sulfides [6]. The discovery of Li10GeP2S12 solid electrolyte called LGPS structured sulfide electrolyte have shown great potential to replace liquid electrolyte as ionic conductivity of LGPS was found 1.2×10-2 S cm-1 at room temperature comparable to the conductivity of organic liquid electrolyte [7]. However, Li10GeP2S12 electrolyte suffers with poor cyclability in solid state batteries due to reduction of Ge+4 ions to Ge0, and instable against lithium metal anode. Moreover, germanium (Ge) is a rare and expensive element, which limits the industrial application of Li10GeP2S12 [8, 9].Therefore, in the present work, we have developed LGPS structured based new Ge free solid electrolytes with high conductivity and better electrochemical stability. The phase identification of newly synthesized solid electrolytes is done by X-ray diffractometer technique along with Rietveld refinement analysis. The conductivity of prepared solid electrolytes is determined by electrochemical impedance spectroscopy. The ionic conductivity of newly synthesised electrolytes has reached upto 0.67 mS cm-1 at room temperature. The electrochemical analysis of prepared solid electrolytes is done using Li-metal in both side (in symmetric cell) as well as using standard cathode and anode materials (full cell).

Lignin-Based Electrolytes for Redox Flow Batteries

Redox flow batteries (RFBs) are promising candidates for long duration energy storage applications thanks to their unique feature of independent scaling of energy and power. Organic electrolytes and an alternative to the present metal-based have been proposed as potentially low-cost and environmentally friendly electrolytes to alleviate the capital costs of RFBs. Lignin, the second most abundant bio-based polymer in nature, demonstrates the advantages of high carbon content, rich in aromatic groups and is a potential electrolyte basefor RFBs [1] [2] [3] [4]. In this work, soda lignin was considered as redox species modified in optimum oxidative conditions. The cyclic voltammetry analysis confirmed its electrochemical reversibility, so that for RFB tests, modified soda lignin was used on the negative side versus ferrocyanide on the positive at highly alkaline media.Following RFB cycling tests, a substantial improvement was achieved in the charge/discharge capacities and coulombic efficiency of RFB using modified soda lignin compared to pristine. For further performance optimization, it was found that the flow ratehas a substantial influence. This is more likely due to the thixotropic behaviour of the lignin electrolyte. Further explorations are under way of studying different membranes/electrolyte additives and cycling with higher concentration of lignin towards enhancing the RFB performance by improving the conductivity thus voltage efficiencies. Thecurrent approach of introducing bio-based electrolytes could enlighten a new path in the future research direction of organic RFBs and add a valuable point towards the carbon neutralization. Keywords: Lignin, Bio-based electrolyte, Organic redox flow battery, Sustainability, Energy storageAcknowledgement:The authors acknowledge Miscancell, Hondiusstraat 28, 6827 DE Arnhem, Netherlands for providing the lignin material for this work.

(Invited) Revealing Charge Storage Processes at the Interfaces of Supercapacitor Electrodes

The fast development of electrochemical energy storage devices has revolutionized almost every aspect of modern life by enabling portable electronic devices, electric vehicles, and grid storage of renewable energy. To satisfy the growing industrial and consumer needs for energy storage systems with high output power and short recharge time, the electrode materials should have excellent high-rate performance.1 Electrical double-layer (EDL) capacitors exhibit high-rate capability and long-cycling life as they store charges electrostatically. Using ionic liquid (IL) as the electrolyte leads to a large voltage window but low capacitance. In this first session of the presentation, I will introduce a mathematical model to simulate the IL ion packing structure in nanopores. This model is capable of estimating the EDLC capacitance based on pore size distribution. Then, we further revealed that mixture IL ions can be selectively driven into the pores of different confinement levels, which was confirmed by solid-state NMR, and further explained by DFT simulation2.In the second part of the presentation, I will shift to pseudocapacitors, which are expected to have a much higher charge storage capacity than EDL capacitors and a much higher rate than batteries as they store energy through fast surface redox reactions.3 The emerging 2D material family, 2D transition metal carbides/nitrides MXenes, shows outstanding pseudocapacitive performance due to their ionophilicity, metallic conductivity, and highly reactive surfaces. The proper coupling between electrolyte and electrode is critical to increase energy and power density. In the organic electrolyte, we found that the solvent has a strong impact on the ion/solvent arrangement in 2D MXene material and hence the charge storage capability.4 In the aqueous electrolytes, we successfully introduced surface redox reactions to MXene electrodes by using the water-in-salt electrolytes and by adjusting the initial valence of Ti in Ti3C2 MXenes, which dramatically increases the capacitance of MXene in the neutral aqueous electrolytes5.References Simon, P.; Gogotsi, Y., Nat. Mater. 2020, 19 (11), 1151-1163. Wang, X.; Mehandzhiyski, A. Y.; et al., J. Am. Chem. Soc. 2017, 139 (51), 18681-18687. Fleischmann, S.; Mitchell, J. B.; et al., Chem. Rev. 2020, 120 (14), 6738-6782. Wang, X.; Mathis, T. S.; et al., Nat. Energy 2019, 4 (3), 241-248. Wang, X.; Mathis, T. S.; et al., ACS Nano 2021, 15 (9), 15274-15284.

Structure-Controlled Prussian Blue Analog as a Cathode Material for Long-Life Seawater Batteries

Nowadays, as the use of fossil fuels is suppressed for achieving carbon neutrality, rechargeable battery is considered as a key factor to lead sustainable society. As far, the most developed and already commercialized batteries are lithium-ion batteries (LIBs). However, as the demand for LIBs is increasing, there are also several issues in the process of obtaining high-performance batteries. First, as the price of raw materials in LIB rises rapidly, a cost issue arises. In addition, as the fire accidents have occurred consistently due to overcharging or use of organic electrolyte, safety concerns are being raised. Finally, the environmental issues are emerging in the process of mining raw material and disposal of waste batteries. Therefore, a cheap, safe, and environmentally friendly battery system is needed as an alternative to LIBs.In this situation, a battery system called seawater battery (SWB) using seawater as a raw material is attracting attention. Since seawater is super-abundant resource, accounting 97% of the earth’s water, the material and manufacturing cost can be effectively reduced. Also, since it is operated in seawater, it is free from fire hazard and environmentally benign. In addition, as natural seawater can be used without additional treatment, energy can be reduced used for refining raw materials in LIBs.Likely to other battery systems, SWB consists of anode, cathode and separator. In anode part, Na-ions originated from NaCl in seawater are plated and stripped during cycling process. For facile metal plating, the anode part is filled with organic electrolyte, which also broaden the operation voltage window of overall cell. The ceramic solid electrolyte is used as separator, which is called Na-ion selective membrane, NASICON. The cathode part contains seawater which can act as an electrolyte or cathode as well (catholyte).The reaction mechanism mechanisms of cathode part can be sorted into three types―Na-intercalation, oxygen evolution/reduction reaction, and Cl-capturing. Herein, we have focused on the intercalation cathode to realize long-life and stable SWB, which is critical properties for large-scale energy storage systems. For intercalation cathode material, Prussian blue analog (PBA) was selected. PBA is an analog form of Prussian blue (PB). Since PB/PBAs have frame-like structures consist of metal nodes and cyanide ligands, the big alkali ions including Na-ions can be inserted and released through interstitial sites. By substituting the iron of PB to other transition metals, various form of PBAs can be synthesized. Among them, Ni-based PBA (Na2Ni[Fe(CN)6] when fully sodiated) was selected, because it is known as stable in seawater and undergoing small volume change during repeating ion (de)insertion, which is advantageous properties for stable SWB application.However, during synthetic process of PBAs, when metal ions and ligands meet rapidly, vacancies are easily created inside the structure. In these empty sites, the water molecules tend to coordinate, becoming crystal water. Since crystal water negatively affects the electrochemical performance of PB/PBAs, it should be controlled. Therefore, we have controlled the structure of Ni-based PBAs by chelation and improved the electrochemical performance of SWBs.By aid of chelating agent, well-structured Ni-based PBA was successfully synthesized. The defect ratio was effectively reduced from 40% to 6%, followed by less crystal water and more Na-ions inside the structure. When applied to SWB system, the cycle performance of chelated PBA was superior to untreated PBA, exhibiting capacity retention of 92.8% after 2000 cycles at 5 C. In conclusion, showing stable and reversible operation during 2000 cycles at the first time in SWB field, PBA-based SWB showed potential to be a promising next-generation battery. Figure 1

Tuning the Interfacial Chemistry for Stable and High Energy Density Aqueous Sodium-Ion/Sulfur Batteries

The environmental-related issues arising from the fossil fuel assorted industrial revolution and worldwide development have prompted the quest for rechargeable batteries. In these predicaments, lithium-ion batteries (LIBs) took ownership to reshape our lives. However, the limited abundance, non-uniform geographical distribution and severe flammability of organic electrolytes, increase the uncertainty over their large-scale application. Recently, aqueous rechargeable sodium-ion batteries (ARSIBs) have gained considerable curiosity for large-scale energy storage due to their much-assured safety, environment friendliness, high-rate capacity, and low cost. However, the prospects of ARSIBs seeing commercial success remained remote due to the narrow water stability window (1.23 V), which translates into low cell voltage (< 1.6 V), low energy density (< 70 Wh Kg-1), and compromised cycling stability. The aforesaid dilemmas can be resolved by generating a protective layer known as a solid electrolyte interface (SEI) like in organic electrolytes. However, the SEI concept in aqueous electrolytes is relatively unexplored, as water dissociation leads to O2 and H2, and will enhance the parasitic reactions. The SEI formed in WiSE due to salt reduction is often inhomogeneous with a porous mosaic structure and is susceptible to mechanical cracking, and increase the overall cost. Hence, high-capacity electrodes and high voltage electrolytes capable of forming a stable SEI are urgently required to fulfill the dream of the large-scale application of ARSIBs.Recently low cost, highly abundant sulfur-based electrode material has attracted significant research attention due to its high theoretical capacity (1675 mA h g-1) and energy density. However, sluggish sulfur redox kinetics, acute polysulfide shutting, dendritic growth on the metal-based anode and low conductivity of sulfur and its discharge products proves to be a major roadblock for its commercialization. Utilizing abundant sulfur in an aqueous electrolyte along with abundant Na+ can resolve the kinetics and conductivity anxieties and leads to a new greener and safer Na-ion/S batteries chemistry. However lower order polysulfide dissolution in water is more feasible, leading to the rapid capacity decay and active sulfur loss due to H2S formation. Polysulfide dissolution is an interfacial mechanism occurring at the electrode-electrolyte interface and depends on both electrode and electrolyte merits. Therefore, an effective approach will be to couple efficient sulfur host with an electrolyte capable of generating a stable SEI on the electrode surface to prevent the direct attack of water on polysulfide.Herein we have explored urchin-like CoWO4 as a sulfur host coupled with Na-W-U-D electrolyte. The CoWO4 exhibits high conductivity, strong chemical interaction for sulfur and its discharge products, and urchin-like morphology having exposed edges facilitate the charge transport results in excellent polysulfide redox kinetics. The high voltage Na-W-U-D electrolyte was prepared by mixing NaClO4, urea, and N, N-dimethylformamide DMF in 1:2:1 ratio in water. Each component in the electrolyte plays an important role. Urea has very high water solubility and tends to form stable SEI, while DMF has a high dielectric constant, good solvation ability, and develop stabilize SEI. As a result, Na-W-U-D shows a stability window close to the 3.1 V regime due to reduced water activity resulting from complex ion solvent interaction and stable and uniform SEI formation, consisting of Na2CO3, polyurea, and reduction products of DMF. Despite the addition of DMF, non-flammable features of aqueous electrolytes remain well maintained. Herein for the first time, the SEI concept was successfully used for the aq. Na-ion/S battery. We discovered that the lower water activity of Na-W-U-D electrolyte hindered polysulfide dissolution and stable SEI prevent the direct attack of water on polysulfide and results in extended cycling stability. At the same time, the urchin-like CoWO4 host enhances the sluggish polysulfide redox kinetics and provides an abundant anchoring site for polysulfide adsorption. We investigate the effect of time, C-rate, depth of discharge, and dissolved oxygen on polysulfide dissolution and self-discharge of the negative electrode. The high electrode capacity combined with the safety and stable SEI of Na-W-U-D electrolyte translated into a record high initial capacity of 834 mA h g-1 w.r.t sulfur, with remarkable cycling stability up to 500 cycles @ 0.5 C. Post analysis by SEM and XPS, evident that the stable SEI consists of Na2CO3, polyurea, and reduced products of DMF (CO and NHMe2), which also prevent the negative electrode from self-discharge by mitigating the parasitic reaction of dissolved oxygen in the electrolyte. Moreover, a full cell assembled by integrating S@CoWO4 anode and Na0.44MnO2 cathode showed remarkable stability and a high energy density of 119 Wh kg-1, making it a promising candidate for a future energy storage system. Figure 1

Proposal and Fundamental Investigation of Energy Storage and Hydrogen Supply System Using the Lithium

In recent years, variable renewable energy such as solar power and wind power spreads rapidly. At the same time, taking measures against output fluctuations and utilization of surplus electricity become important issues. Conversion of electricity to hydrogen is considered as one of the utilizations of surplus electricity [1]. The hydrogen is stored and can be supplied to the fuel cell vehicles according to demand, regardless of weather or time. However, the disadvantage of hydrogen is its low energy density. Although several methods have been investigated for high-density storage of hydrogen, there are still issues about safety, energy loss, cost, and durability [2].In this study, we propose a new energy storage and hydrogen supply method using lithium (Figure 1). The surplus electricity can be converted by the following reaction, and the energy is stored as the lithium.Li+ + e- → Li (-3.04 V vs. SHE) (1)4LiOH → 4Li+ + O2 + 2H2O + 4e- (0.41 V vs. SHE) (2)The lithium can be stored at room temperature and pressure, and its volumetric energy is higher than that of conventional hydrogen storage methods. When hydrogen is needed, the system can be discharged to produce hydrogen by the following reaction.Li → Li+ + e- (-3.04 V vs. SHE) (3)2Li+ + 2H2O + 2e-→ 2LiOH + H2 (-0.82 V vs. SHE) (4)Since the lithium is highly reactive, discharge reaction with water occurs, and hydrogen can be produced without energy input from the outside. As shown in Equation (2) and Equation (4), charge and discharge reactions at the cathode are different, and this system combines the characteristics of lithium-air cell [3] and lithium-water cell [4]. This system has a potential to utilize the surplus electricity; but it has not been fully evaluated from the viewpoint of hydrogen production [5]. Therefore, present study investigated the characteristics of the discharge reaction and hydrogen production behavior.Figure 2 shows experimental cell. The composite anode was water-stable and had a multilayer structure [6]. LATP (Li1+x+yAlxTi2-xSiyP3-y, Ohara Co., Kanagawa, Japan), which is a water-stable lithium-ion-conducting glass ceramic, was used, along with PEO18LiTFSI as the organic electrolyte. The lithium foil and polyethylene oxide (PEO) membrane were sealed inside the cell to prevent direct contact with water vapor and oxygen. Since the cell resistance depends on the temperature, the composite anode was kept at 70°C. For the cathode, glassy carbon rod was used.Figure 3 shows current-voltage (I-V) characteristics. The cathode potential at low-current discharge is higher than theoretical value (-0.82 V). It was caused by reaction with dissolved oxygen in the electrolyte. As the current value is increased, the cathode potential drops sharply, and many bubbles were observed on the cathode end face. It is thought that oxygen concentration overvoltage increased significantly and the discharge reaction with water (hydrogen production as shown in Equation (4)) was occurred.The volume of the produced bubble was measured with using a sealed cathode and adding a liquid level gauge (not shown in Figure 2). As a result, the measured volume showed good agreement with the theoretical hydrogen volume produced by the reaction of Equation (4). It is considered that the reaction shifts to hydrogen production and the effect of dissolved oxygen can be negligible at sufficiently low cathode potential (i.e. high current discharge).The efficiency of this system was estimated by using the obtained experimental results. Generated electricity and enthalpy of produced hydrogen was calculated. When a 20 μA discharge test was conducted by using experimental cell, the discharge efficiency and conversion rate to hydrogen were 30% and 39%, respectively. For comparison, the experimental cell was converted to the lithium-air battery mode and discharged at 20 μA. The discharge efficiency was 56%. Considering the conversion ratio of lithium to electricity and hydrogen, the proposed hydrogen supply system using the lithium can utilize the variable renewable energy.

Design of High-Entropy Electrolytes Enabled By the High-Throughput and Autonomous Procedure

Electrolytes in Li-ion batteries play a significant role as they influence different aspects directly related to the battery performance, such as safety, voltage window, electrochemical stability, and the formation of solid-electrolyte interphase (SEI). Conventionally, these electrolytes are composed of a lithium salt dissolved in an organic solvent such as ethylene carbonate and propylene carbonate. Regarding safety, these organic electrolytes can be replaced by room-temperature ionic liquids (RTILs), which present lower vapor pressure and non-flammability.1 Moreover, adding polymer to these liquid electrolytes to form polymer gel electrolytes has proven to be a good strategy to avoid dendritic growth and increase electrolyte stability.2 The properties of RTIL electrolytes containing Li salts have been studied in the last decade. Still, the scope has been limited primarily to simple RTILs consisting of one cationic and one anionic species. Inspired by the success of high-entropy alloys (HEAs) for forming stable solid solutions with excellent mechanical properties,3 the concept of high-entropy materials has been recently transferred to electrolytes, where the effect of mixing multiple Li salts is explored.4 However, the number of compositional combinations increases rapidly when multiple salts, cationic and anionic species are introduced, and the explorable compositional space increases even more when polymers are added to the mixture.Automating the electrolyte preparation and characterization can be the key feature to allow the exploration of all the possible electrolyte combinations. In this work, we explain the first preliminary results obtained from an autonomous preparation and characterization of high-entropy electrolytes composed of a mixture of two different lithium salts in ionic liquids consisting of multiple anionic and cationic species. In addition, the adaptation of the autonomous system of preparation and characterization of liquid electrolytes to polymer gel electrolytes is also proposed and explained. References. (1) Niu, H.; Wang, L.; Guan, P.; Zhang, N.; Yan, C.; Ding, M.; Guo, X.; Huang, T.; Hu, X. Recent Advances in Application of Ionic Liquids in Electrolyte of Lithium Ion Batteries. J. Energy Storage 2021, 40, 102659. https://doi.org/10.1016/j.est.2021.102659.(2) Chen, J.; Wu, J.; Wang, X.; Zhou, A.; Yang, Z. Research Progress and Application Prospect of Solid-State Electrolytes in Commercial Lithium-Ion Power Batteries. Energy Storage Mater. 2021, 35, 70–87. https://doi.org/10.1016/j.ensm.2020.11.017.(3) Yeh, J.-W.; Chen, S.-K.; Lin, S.-J.; Gan, J.-Y.; Chin, T.-S.; Shun, T.-T.; Tsau, C.-H.; Chang, S.-Y. Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes. Adv. Eng. Mater. 2004, 6 (5), 299–303. https://doi.org/10.1002/adem.200300567.(4) Wang, Q.; Zhao, C.; Wang, J.; Yao, Z.; Wang, S.; Kumar, S. G. H.; Ganapathy, S.; Eustace, S.; Bai, X.; Li, B.; Wagemaker, M. High Entropy Liquid Electrolytes for Lithium Batteries. Nat. Commun. 2023, 14 (1), 440. https://doi.org/10.1038/s41467-023-36075-1.

Molecular Design for Organic Redox Flow Batteries

Redox flow batteries have in recent years become an increasingly researched alternative to lithium-ion batteries for stationary energy storage, stabilizing fluctuations between demand and the intermittent electricity production from solar and wind. The most common vanadium redox flow battery technology suffers from high market volatility for vanadium metal. As a potentially more sustainable alternative to the electrolytes based on metal-ions used in e.g. the vanadium RFB, organic redox active species are being developed to store charge. The organic electrolytes used in aqueous organic redox flow batteries (AORFBs) are reaching closer to economic viability in terms of stability and electrochemical properties but is still inferior to its vanadium counterpart in long-term performance.[1]The degrees of freedom when designing organic electrolytes are endless. However, to improve strategies to designing new electrolytes more systematic studies on the working principles behind what makes organic compounds accept and store charge has to be made. Using less electronegative organo-metallic compounds, radical stabilization and multiple electron reactions, are some of these strategies that can be utilized. Figure 1 shows how examples of current parent molecules with functional groups modifications to tailor stability, solubility and electrochemical properties and in various pH regions.[Image]Molecular design can be divided into three important factors that will impact the performance of the electrolyte; electrochemical properties, solubility and stability. The electrochemical properties of the redox active species are essential for the application towards RFBs, regarding potential, electrochemical reversibility, coulombic- and voltaic efficiencies. The second criteria to maintain a reasonable operating energy density of the RFB is to optimise the water solubility, being proportional to capacity and energy density. The organic compounds solubility is highly pH dependent, thus pairings of posolyte and negolyte will need to operate within the same pH range. By substituting different functional groups to the parent molecule, the operating pH of the species can be tailored. Electrolyte conductivity is also an important factor when altering pH or co-electrolytes in terms of efficiency. Stability or capacity decay is the main focal point for AORFBs and limitation of the redox active species. These decay mechanisms can be further categorized into three different types of degradation, all which result in loss of active electrolyte. First, radical-induced reactions given rise to disproportionation or dimerization reactions, second, pH dependent chemical reactions such as hydrolysis, addition, substitution and elimination reactions and third, physical reactions dependent on molecular size and charge, that can supress or promote crossover through the membrane.As of designing structurally novel molecules, the electrochemical properties are the first property that must be assessed followed by solubility and stability. Since there are already some well explored compounds such as anthraquinones and viologens, much research has been put into increasing the solubility and stability for these.[2] The poster aims to highlight the interconnection between the parameters that make these compounds viable for use in AORFBs. Issues such as what has been explored in terms of posolytes, negolytes, alkaline, neutral and acidic electrolytes and what important components are missing for development of AORFB will be discussed.[1] J. Luo, A. P. Wang, M. Hu, and T. L. Liu, “Materials challenges of aqueous redox flow batteries,” MRS Energy and Sustainability, 9, 1–12, 2022, doi: 10.1557/s43581-022-00023-1.[2] Z. Li, T. Jiang, M. Ali, C. Wu, and W. Chen, “Recent Progress in Organic Species for Redox Flow Batteries,” Energy Storage Materials, 50, 105–138, 2022. doi: 10.1016/j.ensm.2022.04.038. Figure 1

Meaningful Metrics for an Efficient Solvent-Free Formulation of Polymer – Argyrodite Hybrid Solid Electrolyte

Solid-state batteries generate huge excitement with the promise of higher energy density than current Li-ion technology, thanks to the use of lithium metal at the anode1. Recent advancements in ceramic electrolytes demonstrate comparable conductivity with liquid ones2. However, the brittleness of ceramics results in mechanical limitations, during both assembly and cycling3, constraining the scale-up of pure-ceramic batteries. Hybrid solid electrolytes (HSE) can overcome this hurdle by combining the superior ionic conductivity of inorganic fillers with the scalable process of polymer electrolytes in a unique material. Depending on the amount of ceramic electrolyte, two types of HSE can be prepared: a ceramic-in-polymer approach, in which the inorganic filler disturbs the polymer crystallinity; and a polymer-in-ceramic system where the organic electrolyte mainly acts as a binder. Many parameters such as polymer molar mass, type and concentration of Li salt, chemistry and size of ceramic particles and the mixing route, make the HSE formulation an intricate process. As a result, there is a large disparity in the reported formulations and performances of HSE4. In particular, most approaches focus on a slurry-assisted preparation, which becomes a limiting factor when using sulfide-based electrolytes, as these ceramics degrade in common solvents used for binder processing5.To circumvent these issues, we propose a novel, solvent-free HSE preparation, combining an organic matrix based on poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide (PEO:LiTFSI), with the highly conductive argyrodite-type Li6PS5Cl. The optimization of the HSE formulation is driven by key metrics, defined as sufficient ionic conductivity (σion ≥ 10-4 S.cm-1 @25°C) and adequate mechanical characteristics (self-standing property and ability to process as thin membrane <100 µm). Through rational screening, we elucidate the impact of formulation parameters and find the organic-to-inorganic ratio, the polymer molar mass and the ratio of mixed polymer lengths to be factors of paramount importance. Our methodology leads to an optimized formulation of the HSE with high ceramic content (75 wt.%) that meets the fixed criteria. Furthermore, we introduce an activation mechanism fitting (Arrhenius or Vulger-Tammann-Fulcher) as a new and effective metric to unravel the ionic pathway within the HSE. A shift in both ionic conductivity, mechanical cohesion and type of activation mechanism is observed at a unique threshold of 75 wt.% ceramic content. We show that our optimized polymer-in-ceramic HSE provides enhanced conduction through the ceramic network (10-4 S.cm-1 @25°C), displaying an Arrhenius activation, compared to ceramic-in-polymer HSEs, which behave as conventional PEO:LiTFSI following a VTF model. This gain in conductivity coincides with a higher mechanical resistance, as confirmed by tensile test on HSE membranes. Probing the compatibility of the organic and inorganic phases, using electrochemical impedance spectroscopy (EIS) alongside solid-state nuclear magnetic resonance (ssNMR), reveals the formation of an interphase, the quantity and resistivity of which grow with time and temperature. Finally, electrochemical performances are evaluated by assembling an HSE-based battery, which displays comparable stability as pure-ceramic ones (> 100 cycles before reaching 20% capacity loss at C/5) but still suffers from higher polarization and thus lower capacity (130 vs 150 mAh.g-1 at C/20). Janek, J. et al., Nat Energy 1, 16141 (2016).Abakumov, A. et al., Nat Commun 11, 4976 (2020).Doux, J.-M. et al., J. Mater. Chem. A 8, 5049–5055 (2020).Horowitz, Y. et al., J. Electrochem. Soc. 167, 160514 (2020).Ruhl, J. et al., Adv. Ener. Sust. Res. 2, 2000077 (2021).

Intercalated Redox-Active Anions in Layered Double Hydroxides: Toward New Electrode Designs

Layered Double Hydroxides (LDHs) are a versatile class of 2D materials, which consist of layered di- and trivalent metal cation hydroxides with intercalated anions (1). They are used in many applications including energy storage electrodes, water purification or drug delivery (2, 3).In this new study, Anthraquinone-2-sulfonate (AQS) intercalated in the LDH structure of Mg2Al(OH)6, has been investigated and a charge capacity of 100 mAh g-1 has been measured. However, the dissolution of reduced AQS into the aqueous electrolyte occurs from the first reduction leading to a drastic capacity fade upon cycling.To get around the dissolution issue, we synthesize a new intercalated LDH using ferrocene as the redox active moiety. Electrodes with this new LDH material Mg2Al(OH)6-Fc (Figure 1A) showed more stable cycling when used in combination with aqueous or organic electrolytes. However, the most significant increase in cycle life was achieved by operating this electrode in highly concentrated, highly viscous ionic liquid based electrolytes such as Pyr13TFSI. Over 97 % capacity retention was achieved after 200 cycles with a coulombic efficiency close to 100 % (Figure 1B). The higher stability of redox active anions working at positive redox potentials like ferrocene in the LDH structure is a key parameter to improve cycling ability. Moreover, the limited solubility of the intercalated redox anions into the high concentrated ionic liquid electrolyte is also a key factor for improving cycle life of this new electrode.Figure 1: A) Schematic structure of Mg2Al(OH)6-Fc, C) Improved cycling stability of Mg2Al(OH)6-Fc based electrodes in ionic liquid electrolyte Pyr13TFSI. Figure 1