New Class Of Electrolytes Research Articles

Non-Combustible Electrolyte for Fast Charging Lithium-Ion Batteries

Lithium ion batteries (LIBs)-powered electric vehicles have been increasing their share in the market. Currently, the commercially available charging rate is 0.3C, which takes more than 3 hours to fully charge. This is a factor that causes inconvenience to customers. In the case of fast charging, however, lithium dendrites are formed in the battery, which deteriorate battery life and cause battery short circuits leading to fire and explosions. In the event of an electric vehicle fire, the combustible organic solvent in the electrolyte acts as fuel. Although it is evident that safety of transportation should be guaranteed, electric vehicles fires occur frequently and users are concerned about this. Addressing battery safety issue, herein, we report development of a new class of electrolyte that is non-combustible and capable of 10 times faster charging than the commercial one. In this meeting, the effects of non-combustible electrolyte on anode and cathode interfaces under fast charging condition will be discussed. Acknowledgements This research was supported by the National Research Foundation grant funded by the Ministry of Science and ICT (RS-2023-00217581, RS-2023-00260261) of Korea.

Intelligent Nano‐Colloidal Electrolytes for Stabilizing Lithium Metal Anodes: A Review

AbstractAlthough Li‐metal has been revisited as the most attractive anode in building high‐energy‐density batteries owing to its superiority, such as ultimate theoretical capacity and lowest working voltage, notorious Li dendrite growth has plagued its practical uses. Since dendritic Li electroplating is mostly caused by poor Li+ transport and inferior stability of solid‐electrolyte interphase (SEI), an innovative reframing of the electrolyte is crucial to the success of Li‐metal anodes (LMAs). This review presents a new class of electrolytes, nano‐colloidal electrolytes (NCEs), providing a new avenue for next‐generation Li‐metal batteries (LMBs). Without searching for new salts/solvents or their compositional tuning, NCEs exploiting multi‐functional nanoparticles dispersed in liquid electrolytes can promote Li+ transport and reinforce the SEI of liquid electrolytes that are solely used. This review discusses various types of nanoparticles and their key roles in demonstrating excellent suppression of Li dendrite growth and enhancing the cycling stability of LMBs. Unraveling the underlying design principles of NCEs offers practical solutions for stabilizing LMAs, paving the way for developing intelligent battery systems.

Continuous medium approach to approximate the high concentrated aqueous electrolyte with different types of electrochemical structure.

Superconcentrated aqueous electrolytes have recently emerged as a new class of electrolytes, called water-in-salt electrolytes. They are distinguished, in both weight and volume, by a quantity of salt greater than water. Currently, these electrolytes are attracting major interest, particularly for application in aqueous rechargeable batteries. These electrolytes have only a small amount of free water due to an ultrahigh salt concentration. Consequently, the electrochemical stability window of water is wider than the predicted thermodynamic value of 1.23V. Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been shown to be shifted to more negative and positive potentials, respectively. The decrease in free water population is recognized as being involved in the increase in the electrochemical stability window of water. Here, we study the quantitative contribution of the decrease in the free water molecule concentration to the permittivity of the solution and of the activity of water to the OER and HER overpotentials when the salt concentration increases. We compare our model with that of Kornyshev and get three types of electrolyte structures: diluted, gradient of water contents, and aggregation. The theoretical calculation of the redox potentials of the OER and HER is compared with the experimentally determined electrochemical properties of aqueous LiTFSI electrolytes.

(Invited) Modeling of the Bulk and Electrical Double-Layer Structures of Localized High-Concentration Electrolytes

A new class of electrolytes, localized high-concentration electrolytes (LHCE), have shown many benefits to high-capacity electrodes (lithium (Li)-metal, silicon, sodium, zinc, and potassium).[1] These electrolytes combine high-concentration electrolytes (HCE) with salt and solvent with low-viscosity diluents. The dilutes were added to increase ionic conductivity while the locally highly concentrated salt-solvent clusters will facilitate stable solid-electrolyte interphase (SEI) formation while preventing metallic-dendrite formation. For example, it was demonstrated that an LHCE based on lithium bis(fluorosulfonyl)imide (LiFSI) salt, Dimethoxyethane (DME) solvent, and tris(2,2,2-trifluoroethyl)orthoformate (TFEO) diluent (e.g., LiFSI-1.2DME-2TFEO by mol) forms inorganic-rich, monolithic SEI and shows excellent cycling performance for Li-metal batteries under practical conditions.[2] Here, the interactions among cations, anions, solvent molecules, and diluent molecules create a complex design space, making the trial-and-error empirical approach less efficient.Using density functional theory and classical molecular dynamics simulations, we reveal several important design principles:a) The dielectric constant of the pure solvent or diluent is not a good descriptor to describe the solubility of the salt in solvent and diluent.b) The single ion–solvent (diluent) binding energy is insufficient to predict the solubility, which also depends on the molecular structures and the corresponding solvation shell structure.c) The salt-solvent, salt-diluent, and diluent-solvent solubilities jointly determine the solvation structures in LHCE. For example, at certain concentrations, the Li+ solvation shells contain both anions and solvent molecules with minimal participation of the diluent molecules. The local salt concentration can be even higher than its counterpart in the HCE. These simulated solvation structures in bulk electrolytes compare well with Raman spectrum and SAXS data.d) Moreover, the solvation structures are temperature-sensitive. We revealed why the local salt concentration is higher at a certain temperature by MD simulations, which is further validated through Raman deconvolution analyses.e) The SEI formation is sensitive to the electrolyte structure near a charged surface. Therefore, the electrical double-layer (EDL) structure of LHCE needs to be resolved. Here we give a statistical representation of the LHCE in the EDL and show how it differs from the bulk structure and its impact on SEI formation.Reference:[1] J. Electrochem. Soc., 2021, 168, 010522[2] Nat. Energy 2019, 4, 796-805

Lithium Ion Battery Electrolytes Based on Deep Eutectic Solvents

Deep eutectic solvents (DESs) have emerged as an alternative to both common organic solvents and ionic liquids (ILs). DESs share physicochemical properties with ILs such as low vapor pressure, high thermal stability, while offering advantages such as low toxicity, lower cost, and ease of preparation. Moreover, DESs are attractive candidates for electrochemical applications due to their large voltage windows and solubility properties. DESs as a solvent class share a general composition of a hydrogen bond donor (HBD), typically a polyol, amide, or acid, and a hydrogen bond acceptor (HBA), usually a quaternary ammonium or phosphonium salt. At a specific molar composition of a HBD and HBA, the DES forms a eutectic mixture resulting in a large melting point depression.Despite being widely studied, the microscopic structures of DESs have remained largely uncharacterized. Herein, we present a multitechnique NMR study of ethaline (ethylene glycol + choline chloride). Pulsed field gradient diffusion, nuclear Overhauser effect spectroscopy (NOESY), 13C NMR relaxation experiments are deployed to sample a range of frequencies and modes of motion of the polyol and choline components of the DES. Generally, translational and rotational diffusion of polyols are more rapid than those of choline while short-range rotational motions observed from 13C relaxation indicate slow local motion of ethylene glycol at low choline chloride (ChCl) content.Additionally, we have investigated the solubility properties of several lithium salts (LiTFSI, LiFSI, LiBF4, and LiOAc) in these DESs and utilized the same suite of NMR techniques to understand how they act as solvents. One interesting observation is that the Li+ diffusivity exceeds that of the counterion for TFSI-, but not for FSI-. Finally, large changes in the structural organization of DESs that result from the presence of lithium salts may serve as a guide to the design of a new class of electrolytes for lithium-ion batteries.

Nanoscale structure of a hybrid aqueous-nonaqueous electrolyte.

A new class of electrolytes have been reported, hybridizing aqueous with non-aqueous solvents, which combines non-flammability and non-toxicity characteristics of aqueous electrolytes with the superior electrochemical stability of non-aqueous systems. Here, we report measurements of the structure of an electrolyte composed of an equal-mass mixture of 21m LiTFSI-water and 9m LiTFSI-dimethyl carbonate using high-energy x-ray diffraction and polarized neutron diffraction with isotope substitution. Neutron structure factors from partially and fully deuterated samples exhibit peaks at low scattering vector Q that we ascribe to long-range correlations involving both solvent molecules and TFSI- anions. We compare both sets of measurements with results of molecular dynamics simulations based on a polarizable force field. The structures derived from simulations are generally in agreement with those measured, except that neutron structure factors predicted for two partially deuterated samples show very intense scattering increasing up to the low-Q limit of simulation, indicating a partial segregation between the two solvents not observed in experimental measurements.

Understanding the Capacity Decay of Si/NMC622 Li-Ion Batteries Cycled in Superconcentrated Ionic Liquid Electrolytes: A New Perspective.

Silicon-containing Li-ion batteries have been the focus of many energy storage research efforts because of the promise of high energy density. Depending on the system, silicon generally demonstrates stable performance in half-cells, which is often attributed to the unlimited lithium supply from the lithium (Li) metal counter electrode. Here, the electrochemical performance of silicon with a high voltage NMC622 cathode was investigated in superconcentrated phosphonium-based ionic liquid (IL) electrolytes. As a matter of fact, there is very limited work and understanding of the full cell cycling of silicon in such a new class of electrolytes. The electrochemical behavior of silicon in the various IL electrolytes shows a gradual and steeper capacity decay, compared to what we previously reported in half-cells. This behavior is linked to a different evolution of the silicon morphology upon cycling, and the characterization of cycled electrodes points toward mechanical reasons, complete disconnection of part of the electrode, or internal mechanical stress, due to silicon and Li metal volume variation upon cycling, to explain the progressive capacity fading in full cell configuration. An extremely stable solid electrolyte interphase (SEI) in the full Li-ion cells can be seen from a combination of qualitative and quantitative information from transmission electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and magic angle spinning nuclear magnetic resonance. Our findings provide a new perspective to full cell interpretation regarding capacity fading, which is oftentimes linked almost exclusively to the loss of Li inventory but also more broadly, and provide new insights into the impact of the evolution of silicon morphology on the electrochemical behavior.

(Digital Presentation) Fundamentals of Deep Eutectic Solvents As Electrolytes for Lithium-Ion Batteries

Deep eutectic solvents (DESs) have emerged as an alternative to both common organic solvents and ionic liquids (ILs). DESs share physicochemical properties with ILs such as low vapor pressure, high thermal stability, high viscosity while offering advantages such as low toxicity, lower cost, and ease of preparation. Moreover, DESs are attractive candidates for electrochemical applications due to their large voltage windows and solubility properties. DESs as a solvent class share a general composition of a hydrogen bond donor (HBD), typically a polyol, amide, or acid, and a hydrogen box acceptor (HBA), usually a quaternary ammonium or phosphonium salt. At a specific molar composition of a HBD and HBD, the DES forms a eutectic mixture resulting in a large melting point depression due to extensive hydrogen bonding between the components.Despite being widely studied, the microscopic structures of DESs have remained largely uncharacterized. Herein, we present a multitechnique NMR study of two DESs: glyceline (glycerol + choline chloride) and ethaline (ethylene glycol + choline chloride). Fast-field cycling 1H relaxometry, pulsed field gradient diffusion, nuclear Overhauser effect spectroscopy (NOESY), 13C NMR relaxation, and pressure-dependent NMR experiments are deployed to sample a range of frequencies and modes of motion of the polyol and choline components of the DES. Generally, translational and rotational diffusion of polyols are more rapid than those of choline while short-range rotational motions observed from 13C relaxation indicate slow local motion of glycerol at low choline chloride (ChCl) content. We show how the additional hydroxyl group present in glycerol contributes to not only higher viscosities, but a larger perturbation of the hydrogen bonding network by the addition of ChCl.Additionally, we have investigated the solubility properties of several lithium salts (LiTFSI, LiFSI, LiPF6, LiBF4, and LiOAc) in these DESs and utilized the same suite of NMR techniques to understand how they act as solvents. We observe that due to anion effects, the heterogeneities present in DES result in differential solvation for some species where there is a distinction of lithium salts co-existing in these holes as well as the bulk. The large changes in the structural organization of DESs that result from the presence of lithium salts will serve as a guide to the design of a new class of electrolytes for lithium-ion batteries.

Glyoxal-based electrolytes for potassium-ion batteries

In this study we reported for the first time the use of an electrolyte containing 1.5 M KFSI (potassium(bis)-fluorosulfonylimide) dissolved in a mixture of propylene carbonate (PC), tetraethoxy-glyoxal (TEG) and vinyl-ethylene carbonate (VEC) in potassium-ion batteries (KIB). We showed that this electrolyte displays good transport properties, high thermal stability and broad electrochemical stability. Graphite and Prussian White (PW) electrodes used in combination with 1.5 M KFSI in PC/TEG display high capacity, even at high C-rates, and remarkable cycling stability. These electrodes can be successfully combined in a KIB displaying high efficiencies and high stability for more than 500 cycles. Considering these results, glyoxal-based electrolytes can be therefore considered as an attractive new class of electrolyte for KIBs.

Soft X-ray Emission Studies on Hydrate-Melt Electrolytes.

Highly salt-concentrated aqueous solutions are a new class of electrolytes, which provide a wide potential window exceeding 3 V and, hence, realize possibly inexpensive, safe, and high-energy-density storage devices. Herein, we investigate the evolution of the coordination structure and electronic state depending on the salt concentration through soft X-ray emission spectroscopy and first-principles molecular dynamics calculations. Close to the concentration limit, categorized as a "hydrate melt," a long-range hydrogen-bond network of water molecules disappears with emerging localized electronic states that resemble those in the gas phase. Such localized electronic states are attributed not only to their geometrically isolated nature but also to their dominant electrostatic interaction with Li+ cations. Therefore, the electrical properties of water in the hydrate melt can be more gaslike than liquidlike.

Organosulfide‐Based Deep Eutectic Electrolyte for Lithium Batteries

AbstractDeep eutectic electrolytes (DEEs) are a new class of electrolytes with unique properties. However, the intermolecular interactions of DEEs are mostly dominated by Li⋅⋅⋅O interactions, limiting the diversity of chemical space and material constituents. Herein, we report a new class of DEEs induced by Li⋅⋅⋅N interactions between 2,2′‐dipyridyl disulfide (DpyDS) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The strong ion‐dipole interaction triggers the deep eutectic phenomenon, thus liberating the Li+ from LiTFSI and endowing the DEEs with promising ionic conductivity. These DEEs show admirable intrinsic safety, which cannot be ignited by flame. The DEE at the molar ratio of DpyDS:LiTFSI=4:1 (abbreviated as DEE‐4:1) is electrochemically stable between 2.1 and 4.0 V vs. Li/Li+, and exhibits an ionic conductivity of 1.5×10−4 S cm−1 at 50 °C. The Li/LiFePO4 half cell with DEE‐4:1 can provide a reversible capacity of 130 mAh g−1 and Coulombic efficiency above 98 % at 50 °C.

Organosulfide-Based Deep Eutectic Electrolyte for Lithium Batteries.

Deep eutectic electrolytes (DEEs) are a new class of electrolytes with unique properties. However, the intermolecular interactions of DEEs are mostly dominated by Li⋅⋅⋅O interactions, limiting the diversity of chemical space and material constituents. Herein, we report a new class of DEEs induced by Li⋅⋅⋅N interactions between 2,2'-dipyridyl disulfide (DpyDS) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The strong ion-dipole interaction triggers the deep eutectic phenomenon, thus liberating the Li+ from LiTFSI and endowing the DEEs with promising ionic conductivity. These DEEs show admirable intrinsic safety, which cannot be ignited by flame. The DEE at the molar ratio of DpyDS:LiTFSI=4:1 (abbreviated as DEE-4:1) is electrochemically stable between 2.1 and 4.0 V vs. Li/Li+ , and exhibits an ionic conductivity of 1.5×10-4 S cm-1 at 50 °C. The Li/LiFePO4 half cell with DEE-4:1 can provide a reversible capacity of 130 mAh g-1 and Coulombic efficiency above 98 % at 50 °C.

A Safer, Wide-Temperature Liquefied Gas Electrolyte Based on Difluoromethane

Development of safe electrolytes that are compatible with both lithium metal anodes and high-voltage cathodes that can operate in a wide-temperature range is a formidable, yet important challenge. Recently, a new class of electrolytes based on liquefied gas solvents has shown promise in addressing this issue. Concerns, however, have been raised on the pressure, flammability and low maximum operating temperature of these systems. Here, we endeavor to mitigate safety and practicality concerns by demonstrating an enhanced safety feature inherent in liquefied gas electrolytes and by showing the viability of using difluoromethane as a liquefied gas solvent which has lower pressure, lower flammability, and improved maximum operation temperature characteristics compared with fluoromethane. We create a custom-built setup to enable liquefied gas electrolyte characterization through Raman spectroscopy and supplement this with molecular dynamics (MD) simulations. The electrolyte shows good conductivity through a wide temperature range and compatibility with both the lithium metal anode and 4 V class cathodes. The demonstrated use of such alternative liquefied gas solvents opens a path towards the further development of high-energy and safe batteries that can operate in a wide-temperature range.

Electrochemistry of PdCl2 at glassy carbon electrode in 1-Ethyl-3-methylimidazolium chloride ionic liquid

Electrodeposition of palladium from ionic liquids has not been actively studied although this new class of electrolytes offer certain important advantages. Further, the application of rotating disc technique for kinetic studies in ionic liquids is scarce, and absent from the studies on Pd. In this work, the rotating disc electrode (RDE) technique was used to study the electrochemistry of PdCl2 dissolved in 1-ethyl-3-methylimidazolium chloride [EMIM][Cl] ionic liquid. Glassy carbon (GC) served as working electrode. The standard electrochemical techniques, such as cyclic voltammetry(CV), linear sweep voltammetry(LSV), chronopotentiometry(CP) and chronoamperometry(CP) were used under rotating and stationary conditions, at standard 100C. CV revealed two cathodic (C1 and C2) and two anodic (A1 and A2) current peaks. We are proposing that both cathodic current peaks belong to the same reduction of PdCl42− reaction, split into two by electrode surface morphology changes; C1 and C2 representing electroreduction of Pd on GC and Pd on Pd, respectively. The first anodic current peak (A1) is not well understood, but the second (A2) clearly distinguishes electrodissolution of Pd with thin film geometry. According to Levich and Levich-Koutecky analysis the first reduction step (C1) is the mixed kinetics, while the second (C2) is the mass transfer controlled. Diffusion coefficients estimated are of ~10−7cm2/s order.Concerning the stages of nucleation and growth of Pd, for the nucleation stage a 2D-instantatneous nucleation mechanism is proposed. The growth is aggregative, made of numerous Pd nanoclusters, consequently not fitting any of the 2D and 3D-growth models.

Polyeutectic-based stable and effective electrolytes for high-performance energy storage systems

Polyeutectic electrolyte, as a new class of electrolytes, was proposed for various high-energy storage systems.

Deep Eutectic Solvents As Sodium-Ion Battery Electrolytes with Increased Durability at Higher Temperatures

Sodium-ion batteries (SIBs) are a potential cost-effective alternative for lithium-ion batteries (LIBs) in applications which require large-scale energy storage. In these applications, low cost and sustainability are of prime importance. The extensive use of LIBs for large-scale storage would drive up lithium prices because of the latter’s limited production. As the lightest and smallest alkali metal after lithium, sodium is abundant and widely available, and is therefore more cost-efficient and sustainable. SIBs can use light and inexpensive aluminum current collectors for both the anode and cathode, as opposed to LIBs, which usually require more expensive copper current collectors for the anodes. This further increases the SIB's viability in applications where cost and sustainability are the most crucial factors.Viable battery electrolytes should have sufficient ionic conductivity, be electronically insulating, have a large electrochemical and thermal stability window, and not show reactivity with the other components of the battery. They should be safe, non-toxic, and inexpensive. Ionic liquids, defined as materials which consist entirely out of ions and which remain liquid below 100 °C, were previously studied as electrolytes for SIBs as they have a high intrinsic ionic conductivity, can dissolve high amounts of salt, are non-flammable and have a high thermal and (electro)chemical stability. Ionic liquids are typically expensive due the difficulty of their synthesis. Deep eutectic solvents (DESs) are closely related to ionic liquids and consist of a mixture of Lewis/Brönsted acids and bases, where the melting temperature of the mixture is below that of the individual components. Whereas DESs and ionic liquids can have similar physical properties, DESs can have additional advantages such as ease of preparation and wide availability of reagents, although this depends on the exact composition. Binary and ternary mixtures of different XFSI (FSI = bis(fluorosulfonyl)imide) and XTFSI (TFSI = bis(trifluoromethanesulfonyl)imide) inorganic salts were previously applied as DES electrolyte in sodium-ion half cells, which were constrained to operation at 80 °C or higher because of their relatively high melting points.1,2 These cells showed high reversibility and high Coulombic efficiency.Other DESs may also offer an increase of the stability of battery operation, and may be used at less stringent temperature conditions (with acceptable ionic conductivity even at room temperature). This stability problem is particularly pronounced at 55 °C or higher for conventional electrolytes, where battery performance rapidly degrades when linear carbonates are used as electrolyte solvent.3 Our series of DESs as SIB electrolytes were based on the dissolution of NaTFSI in an amide which is solid at room temperature. For each electrolyte, the effect of the solution structure on its electrochemical properties was studied. The amide was spontaneously reduced when contacted with sodium metal. By increasing the salt concentration, we observe a lower reactivity with sodium metal, a broader electrochemical stability window and a decreased ionic conductivity due to the strong Coulombic interactions among the amide molecules, Na+, and TFSI- ions (Figure). The sample containing 10 mol% of NaTFSI shows an anodic stability limit of ~3.6 V vs Na+/Na and a conductivity of 10.3 mS cm-1 at 55 °C. A DES with 30 mol% NaTFSI is stable up to ~4.6 V vs Na+/Na and has a conductivity of 3.8 mS cm-1 at 55 °C. The variation of conductivity with temperature of both DESs could be fitted with the Vogel-Tamman-Fulcher equation. At 55 °C, (Na3V2(PO4)3/C)/(Na2+x Ti4O9/C) full cells containing DES as electrolyte demonstrate a considerably higher durability and Coulombic efficiency than cells containing a conventional organic solvent-based electrolyte. As such, these DESs form a new class of electrolytes for application in sodium-ion batteries, offering a more durable performance at 55 °C than conventional systems.References(1) Nohira, T.; Ishibashi, T.; Hagiwara, R. Properties of an Intermediate Temperature Ionic Liquid NaTFSA – CsTFSA and Charge – Discharge Properties of NaCrO2 Positive Electrode at 423 K for a Sodium Secondary Battery. J. Power Sources 2012, 205, 506–509.(2) Fukunaga, A.; Nohira, T.; Kozawa, Y.; Hagiwara, R. Intermediate-Temperature Ionic Liquid NaFSA-KFSA and Its Application to Sodium Secondary Batteries. J. Power Sources 2012, 209, 52–56.(3) Yan, G.; Dugas, R.; Tarascon, J. The Na3V2(PO4)2F3/Carbon Na-Ion Battery: Its Performance Understanding as Deduced from Differential Voltage Analysis. J. Electrochem. Soc. 2018, 165 (2), 220–227. Figure 1

(Invited) Designing New Electrolytes for High-Energy Lithium Metal Batteries

Lithium (Li) metal batteries with conventional nickel-rich transition metal oxide cathodes have been regarded as one of the next-generation high-energy rechargeable battery systems because the Li metal anode has an ultrahigh theoretical specific capacity (3860 mAh g-1) and a very low standard electrochemical redox potential (-3.040 V). However, two major problems associated with Li metal anode ¾ Li dendrite growth during repeated cycling and low Li Coulombic efficiency still hinder the application of rechargeable Li metal batteries, although great progresses have been made in stabilizing Li metal anode in the past decade, including smoothening Li deposition morphology and increasing Li Coulombic efficiency. Among these progresses, the development of novel electrolytes is one of the most important things, which can not only enable Li metal anode to reach high Li Coulombic efficiency of 99.5%, but also stabilize high voltage cathodes up to 4.5 V. In this presentation, the designing principles of solvating solvents and diluents in a new class of electrolytes called localized high-concentration electrolytes for high-energy Li metal batteries will be reported. The mechanisms for the performance advancements by the new electrolytes will also be discussed, especially through the Li/electrolyte and cathode/electrolyte interphases.

Impact of Water on the Properties of Superconcentrated Electrolytes

Superconcentrated electrolytes are a new class of electrolyte that is of interest to the scientific community for battery applications. These electrolytes consist of an amount of salt greater than the amount of solvent, while remaining liquid. It is currently accepted that the reduction of the solvation sphere under these conditions results in a greater electrochemical stability of the solvent and a higher Li+ transport number. These properties, are widely used in the literature For instance, superconcentrated electrolytes employing acetonitrile as the solvent have been applied in lithium metal batteries while acetonitrile with moderate salt concentration decomposes on lithium. Despite the attractiveness of the field to these electrolytes, their properties are still poorly understood, and the methods of analysis used vary between different studies. There is no standard protocol for their use and it becomes difficult to establish correlations between different studies. Our goal is to establish the required methods to standardize the methodology and fill the gaps in the field.To do so, we firstly studied superconcentrated electrolytes based on LiTFSI and acetonitrile. The approach taken highlights the factors that have a significant impact on the properties of electrolytes. One of these factors is the water content. The results demonstrate that the presence of water in the solutions has a limited impact on the physical properties of viscosity and density of the mixtures as long at the concentration remains at and below 1000 ppm. The water content has a significant impact on the electrochemical window of stability of the electrolyte, reducing it to less than 2 V at 1000 ppm. The solvating structure of superconcentrated electrolytes is also studied via the electrochemistry of the Ferrocene/Ferrocenium couple to probe the impact of the electrolyte properties on electron transfer reactions. These results highlight the importance of structure and composition in the development of superconcentrated electrolytes.

Ion transport in topological all‐solid‐state polymer electrolyte improved via graphene‐oxide

AbstractDesigning and constructing novel topological all‐solid‐state polymer electrolyte (SPE) matrices can improve the ionic conducting ability of the prepared SPEs compared with the linear ones. Here, we construct a novel topological polymer electrolyte matrix using triphenylene as core and block poly(methyl methacrylate)‐poly(poly[ethylene glycol] methyl ether methacrylate) as arm. Specifically, the arm is attached onto the core via sequential atom transfer radical polymerization. The molecular weight of the polymers is well controlled via adjusting the inventory rating of monomers, the optimal SPE obtained via solution casting has an ambient temperature ionic conductivity of 3.69 × 10−5 S cm−1, which is higher than typical linear poly(ethylene oxide)‐based SPE (usually 10−6–10−8 S cm−1). The electrochemical performance is further improved through adding given contents of graphene‐oxide into the SPE. Thus, we believe, through molecular designing and the widely used composite tactics, new class of electrolytes with high‐electrochemical performance for all‐solid‐state Li‐ion batteries can be developed.

A new double layer super-capacitor made by free-standing activated carbon membranes and highly concentrated potassium acetate solutions

Water in salt solutions are a new class of electrolytes developed with the aim of increasing the electrochemical stability of aqueous electrolytes without decreasing the transport properties. Among them, aqueous solutions of potassium acetate (CH3COOK, AcK) have received little attention, despite its large solubility in water at room temperature (25 mol kg−1) and the very low cost. With the idea of developing cost-effective and good performing Electrochemical Double Layer Capacitors (EDLCs), a symmetric device based on a low-cost coal derived carbon (F400) and highly concentrated AcK solutions as electrodes and electrolytes, respectively, was fabricated and optimized. The best results are obtained with the system F400/20 mol kg−1 AcK/F400 able to deliver a gravimetric energy density of 26 Wh kg−1 at an average power of 1.4 kW kg−1.