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Combining highly concentrated electrolytes with a polymer network is a valid approach to simultaneously achieve fast Li+ ion transport, high thermal stability, and a wide electrochemical window in a quasi-solid-state form. In this work, flexible gel electrolytes comprising commercially available poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) and highly concentrated electrolytes of Li salts/sulfolane (SL) were prepared by a simple solution casting method. The anionic effects of the gel electrolytes on the Li-ion conductivity and charge transfer kinetics at the gel/electrode interface were investigated. The SL-based gel electrolyte with lithium bis(fluorosulfonyl)amide (LiFSA) showed an ionic conductivity of 0.7 mS cm−1 and a high Li transference number (>0.5) at 30 °C. The charge transfer resistance in a [Li/gel/LiCoO2] cell with LiFSA was lower than that of the cells with lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) or LiBF4, indicating faster interfacial charge transfer kinetics in the gel electrolyte with FSA. The Li/LiCoO2 cell with the LiFSA/SL gel electrolyte exhibited a higher capacity than that of the cells with the LiTFSA/SL and LiBF4/SL gel electrolytes. Hence, rationally designed gel electrolytes containing highly concentrated SL-based electrolytes enable the high rate performance of Li batteries.

The performance of a sodium-ion (Na) battery is significantly influenced by its electrolyte characteristics. In particular, the transport properties of the electrolyte have considerable effects on the discharge rate capability. During discharging of a Na battery at high current densities, a concentration gradient of Na salt develops because both cations and anions are mobile in the liquid electrolyte. Concentration polarization can be suppressed by increasing the Na+ transference number (tNa+) of the electrolyte. This study demonstrates that highly concentrated NaN(SO2F)2 dissolved in 3-methylsulfolane (MSL) exhibits a high tNa+ value of >0.6 under anion-blocking conditions. Raman spectroscopy revealed that Na+ ions formed complexes with MSL and anions in the electrolyte. Na+ ions exchange ligands dynamically and move faster than the ligands, resulting in a high tNa+. The high tNa+ enables a high-rate discharge of the Na battery, despite the low ionic conductivity of the highly concentrated electrolyte.

Ionic liquids (ILs) possess low volatility and low flammability and are promising electrolytes for thermally stable Li-ion batteries (LIBs). Among ILs, bis(fluorosulfonyl)imide (FSI−) anion-based ILs have low viscosity and high ionic conductivity and FSI-based electrolytes are useful for achieving a high power density LIB. In this study, we investigated the effects of LiFSI concentration in IL electrolytes on the performance of LIBs. We prepared electrolytes composed of 1-ethyl-3-methyl imidazolium bis(fluorosulfonyl)imide (EMImFSI) and LiFSI. The ionic conductivity of the electrolyte decreased with increasing LiFSI concentration due to an increase in viscosity; however, the Li+ transference number increased with increasing LiFSI concentration. The IL electrolyte was tested in a LiNi0.5Mn0.3Co0.2O2/graphite pouch cell. The discharge rate capability of the cell was improved by increasing the LiFSI concentration. The higher LiFSI concentration was effective in suppressing the depletion of Li+ in the vicinity of the cathode during the high current discharge. Furthermore, we demonstrated that cells with IL electrolytes can be stably operated over 500 charge-discharge cycles at 25 °C and 60 °C.

For the rapid charge-discharge performance of Li-ion batteries (LIBs), ionic conductivity (σ) and Li ion transference number (t+) are important parameters of electrolytes. Electrolytes with high t+ alleviate the concentration polarization upon fast charge-discharge, and prevent the diffusion-limited mass transfer of Li+ ions. Recent studies have suggested that certain highly concentrated electrolytes exhibit better rate performances than conventional organic electrolytes despite their lower σ. However, the relationship between the transport properties (t+ and σ) of highly concentrated electrolytes and the enhanced rate performance of LIBs is yet to be elucidated. To evaluate the rate performance of LIBs with highly concentrated electrolytes in terms of transport properties, we investigated the discharge rate capability of LiCoO2 (LCO) half-cells using highly concentrated lithium bis(fluorosulfonyl)amide (Li[FSA]) electrolyte in γ-butyrolactone (GBL), acetonitrile (AN), dimethyl carbonate (DMC), and 1,2-dimethoxyethane (DME) solvents. There was a remarkable solvent dependence of t+, and the highest tLi+current of 0.67 was observed for GBL-based electrolyte measured using the very-low-frequency impedance spectroscopy (VLF–IS) method. The LCO half-cell with GBL-based electrolyte delivered higher discharge capacities than the cells with DMC- and DME-based electrolytes at high current densities. The improved rate performance in GBL-based electrolytes was attributable to enhanced Li+ ion mass transfer derived from the high tLi+current. We demonstrated the importance of tLi+current on the rate capability of LCO half-cells with highly concentrated electrolytes for high-rate battery performance.

Highly concentrated Li salt/aprotic solvent solutions are promising electrolytes for next-generation batteries. Understanding the Li+ ion transport process is crucial for designing novel battery electrolytes. In this study, we systematically investigated the phase behavior, solvate structures, and Li+ transport properties of binary mixtures comprising lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and various sulfones, such as sulfolane (SL), 3-methyl sulfolane (MSL), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), and ethyl isopropyl sulfone (EiPS). Except for the MSL system, the [LiTFSA]/[sulfone] = 1/2 mixtures remained in a liquid state at room temperature, thus enabling a systematic comparison of the Li+ transport properties in the highly concentrated electrolytes. In highly concentrated liquid electrolytes, Li+ ions diffuse by exchanging ligands (sulfone and TFSA). Li+ ions diffuse faster than TFSA in all electrolytes except the EiPS-based electrolyte at a composition of [LiTFSA]/[sulfone] = 1/2, resulting in high Li+ transference numbers. SL-based electrolytes show higher ionic conductivity and Li+ transference numbers than other sulfone-based electrolytes. Consequently, sulfone solvents with compact molecular sizes and low energy barriers of conformational change are favorable for enhancing the Li+ ion transport in the electrolytes.

Nanocomposite electrolytes comprising molten Li salt solvates (MLSs) and inorganic fillers provide liquid-like processing and reasonably high Li ion transport properties. Thus, they can be potentially used as thermally-stable and mechanically-robust electrolytes. In this study, nanocomposite electrolytes exhibiting two distinct non-Newtonian rheological responses, i.e., shear thinning and shear thickening behaviors, were prepared using glyme- and sulfolane-based molten Li salt solvates and hydrophilic fumed silica without any surface modification of the silica. The rheological responses strongly depended on the anionic structure of the MLSs. The MLS-silica composites containing bis(trifluoromethanesulfonyl)amide (TFSA) and BF4 anions formed a shear thinning gel and shear thickening fluid, respectively. The characteristic rheological properties (elastic modulus for the shear thinning gel and the maximum peak viscosity and critical shear rate for the shear thickening system) were extensively tailored by the silica content in addition to the chemical structure of the MLSs, while the changes in their ion transport properties were moderate even in the presence of silica fillers.

Ion gels, soft materials that contain ionic liquids (ILs), are promising gel electrolytes for use in electrochemical devices. Due to the recent surge in demand for flexible and wearable devices, highly durable ion gels have attracted significant amounts of attention. In this review, we address recent advances in the development of ion gels that can heal themselves when mechanically damaged. Light- and thermally induced healing of ion gels are discussed as stimuli-responsive healing strategies, after which self-healable ion gels based on supramolecular and dynamic covalent chemistry are addressed. Tough, highly stretchable, and self-healable ion gels have recently been fabricated through the judicious design of polymer nanostructures in ILs in which polymer chains and IL cations and anions interact. The applications of self-healable ion gels to electrochemical devices are also briefly discussed.

ABSTRACT: In recent research, the importance of electrolytes with high Li+ transference number (tLi) and ionic conductivity (σion) has been emphasized to realize rapid charge for Li secondary batteries. Simultaneously fulfilling high tLi and σion is still unsolved in liquid electrolytes; however, highly concentrated electrolytes (HCEs) of weakly coordinating solvents and Li salts will be promising for addressing this challenge. This idea is inspired by a recent study by Angell et al. on superprotonic ionic liquids comprising a weak Brønsted base and a superacid; highly labile and exchangeable H+ can be formed between significantly weak proton accepting sites. Here, we studied weakly coordinating fluoroethylene carbonate (FEC)-based electrolytes with lithium bis(fluorosulfonyl)amide (Li[FSA]) and compared with ethylene carbonate (EC)-based electrolytes. Experimental and computational studies indicated that solvent and ion exchange is more pronounced in the FEC-based HCE, resulting in higher tLiPP (0.73) and ionic conductivity (1.02 mS cm−1) compared to those of the EC-based HCE (tLiPP= 0.53 and σion= 0.84 mS cm−1). However, the FEC-based HCE exhibited lower electrochemical stability due to the intrinsically lower reductive stability of FEC and the oxidative decomposition of the liberated solvent in the HCE. Despite the superior transport properties, the Li/LiCoO2 cell with the FEC-based electrolyte showed lower discharge capacities and lower Coulombic efficiencies at higher current densities due to side reactions of the electrolyte. This study demonstrates that weak Li-solvent interactions can simultaneously enhance tLi and σion of HCEs, but they have the potential to sacrifice the electrochemical stability.

Abstract Polarisation‐state conversion from parallel linear polarisation to orthogonal linear polarisation was successfully demonstrated using a birefringence crystal for the two longitudinal oscillation modes of a dual‐mode Nd:YVO4 microchip laser. The laser emitted two longitudinal oscillation modes simultaneously in the vertical linear polarisation state with a frequency difference of 101 GHz. In the experiment, it was shown that by using a 17‐mm‐long LiNbO3 birefringence crystal, it was possible to almost perfectly convert the polarisation state of the two oscillation modes by providing a π‐rad difference in phase retardations between the two oscillation modes. The residual elliptic component was eliminated using a pair of waveplates.

The high dispersibility of single-walled carbon nanotubes (SWCNTs) in supporting media is a challenge for maximizing the mechanical and electrical properties of SWCNT-based composite materials. Herein, we demonstrate that highly concentrated lithium-salt electrolytes (HCEs) can disperse SWCNTs without using any other dispersing agents. Incorporating SWCNT-dispersed HCEs into a polymer matrix allows the fabrication of mechanically stable, electronically and ionically (Li+) conductive composite gels. Due to its high electronic conductivity and good dispersion of the electrolyte, the SWCNT/HCE composite gel is a promising electrode material for energy storage devices. As a demonstration, the composite gel is applied as a gel cathode for a Li-sulfur battery by incorporating molecular sulfur into the gel, resulting in stable cycling performance. Keywords: Concentrated electrolyte, Single-walled carbon nanotube, Polymer, Conducting material, Li-S battery

Abstract We experimentally show a quantum interference in phase space by interrogating photon number probabilities (n = 2, 3, and 4) of a displaced squeezed state, which is generated by an optical parametric amplifier and whose displacement is controlled by amplitude of injected coherent light. It is found that the probabilities exhibit oscillations of interference effect depending upon the amplitude of the controlling light field. This phenomenon is attributed to quantum interference in phase space and indicates the capability of controlling quantum interference using amplitude. This remarkably contrasts with the oscillations of interference effects being usually controlled by relative phase in classical optics.

The development of suitable separation technologies for the separation of carbon dioxide is a pressing technological requirement. The application of ion gel membranes for this purpose continues to stimulate a great deal of research, and in this study we focus on the chemical structure of the ionic liquid component in the ion gel, and its interactions with the sulfonated polyimide polymer. Whilst such membranes are known to give promising carbon dioxide separation properties together with mechanical strength and thin-film-processability, we further elaborate on how changing the cation of the ionic liquid from a typical imidazolium cation to a protic variant effects the physicochemical, thermal, and structural properties of the membranes, and how these changes further influence the carbon dioxide separation properties. We compare and contrast our findings with our earlier study on protic and aprotic ammonium-based ionic liquids, and highlight that for CO2 absorption behavior in the imidazolium systems, the importance of directionality of interactions (ion pairs exhibit a large energy stabilization only for a specific geometrical arrangement of cation and anion, e.g., hydrogen bonding rather than Coulombic interaction) between cation and anion applies not only to the protic system, but also to the nominally aprotic cation. Finally, we demonstrate that the phase separation behavior in the ion gels is an important factor in determining the carbon dioxide separation behavior.

Abstract The demand for innovative batteries with high specific energy densities has increased. Li‐metal batteries employing Li‐metal anodes, regarded as the ultimate anodes with a high theoretical capacity, have been extensively studied over the past few decades. However, the poor reversibility and safety concerns regarding Li‐metal anodes remain unresolved. The importance of the electrode/electrolyte interface, especially the solid electrolyte interphase (SEI), for achieving reversibility of Li metal anodes has been extensively studied. Herein, we focused on the impact of the Li ion transport properties in oligoether (glyme)‐based electrolytes on the deposition/dissolution efficiency of Li metal anodes. Analysis of the low‐frequency impedance spectra of Li‐plated Cu/Li cells revealed that the diffusion resistance of Li ions (Rdiffusion) may be a dominant contributor to the internal resistance of the cells employing glyme‐based electrolytes. A higher Rdiffusion in poor‐mass‐transport electrolytes with a lower Li ion transference number resulted in larger polarization during Li deposition/dissolution, leading to more pronounced unfavorable side reactions and lower Coulombic efficiency. Rdiffusion rather than interfacial resistance affected the reversibility of the Li metal anode. Enhancing the Li ion mass transport ability of electrolytes is important for achieving highly reversible charge‐discharge performance of Li metal anodes at high current densities.

Li–S batteries have attracted attention as the next-generation secondary batteries. While substantial progress is made in understanding Li–S chemistry at a fundamental level, only a limited number of studies are dedicated to achieving high energy density at the practical pouch cell level. The challenge lies in attaining high-energy-density Li–S batteries under harsh conditions, which involve a minimal amount of electrolyte and a relatively high areal S-loading cathode. This discrepancy creates a substantial gap between fundamental material research and comprehensive cell-level investigations. In this study, it is investigated how the morphology and properties of two carbon materials, namely Ketjen black (KB) and mesoporous carbon nano-dendrites (MCND), influence the composite cathode architecture and determine the performance of Li–S batteries. Unlike KB, MCND allows for a higher sulfur-loading cathode without evident cracks in the composite cathode. This achievement can be attributed to the high porosity, excellent wettability, and high conductivity exhibited during an identical electrode preparation procedure. Furthermore, large-format Li–S pouch cells incorporating MCND/S cathodes are successfully fabricated. These cells demonstrate an energy density surpassing 250 Wh kg−1 and an initial discharge capacity of 3.7 Ah under challenging conditions (S-loading > 5 mg cm−2 and E/S < 3.5 μL mg−1). [ABSTRACT FROM AUTHOR]