Liquid-based Electrolyte Research Articles

On the Parasitic Surface Adsorption of Pyrrolidinium and Phosphonium-based Ionic Liquids Preventing Accurate Differential Capacitance Measurements

Abstract Differential capacitance measurements are known to provide vital information regarding electrical double layer charging as well as interfacial structuring of ionic liquids and ionic liquid-based electrolytes. Several hurdles have prevented these types of measurements from becoming widely used, including the fact that there exists no real consensus as to how the measurement needs to be performed and the results analyzed. To add to the difficulty, some ionic liquids are known to display a hysteresis process, thus inducing measurement variabilities. In this report, we study pyrrolidinium and phosphonium-based ionic liquid electrolytes and show that hysteresis processes indeed exist and that these are mostly the consequence of cationic adsorption on the surface. Atomic force microscopy experiments reveal that pyrrolidinium-based systems display a much denser degree of ionic compaction at the interface, compared to the phosphonium-based systems, a fact that we correlate with the much more intense hysteresis measured in pyrrolidinium-based systems. We further propose a new method for the measurement of differential capacitance and compare it with other methods in use. It is found that the proposed method allows to minimize hysteresis phenomena, thereby leading to better accuracy.

Solid polymer electrolytes with dual salts enhance lithium-metal interfacial stability for long cycle performance of lithium batteries

Solid-state lithium metal batteries (LMBs) are considered to be the ideal energy storage system for achieving higher energy density and high safety. However, poor physical contact at the interface between the solid-state electrolyte and lithium metal, as well as the growth of dendrites make the cycling stability of LMBs challenging. Therefore, we developed a multifunctional ionic liquid-based polymer electrolyte including montmorillonite (MMT) and double salts (NaFSI and LiTFSI). The self-concentration effect of MMT lithium ions, combined with the electrostatic shielding effect of the double salts, resulted in homogeneous ion deposition, reducing dendritic lithium generation and improving lithium battery performance, with lithium batteries achieving a stable cycling rate of 1000 cycles at 1 C. Moreover, Due to the integrated assembly of the battery assembly process using light curing, the physical interface between the positive electrode-electrolyte-negative electrode achieves good contact and wettability. NaFSI achieves the enhancement of solid electrolyte interface (SEI) by introducing NaF/LiF to SEI of lithium metal, and the optimization of ion deposition pattern at the interface can be achieved by electrostatic shielding effect. Ultimately, stable ion transport at the solid-solid interface for lithium metal solid-state batteries can be realized. Notably, the ionic liquid-based polymer electrolyte with high ionic conductivity (1.2 × 10−3 S cm−1) and high oxidative stability (5.2 V vs. Li/Li+) at room temperature. In addition, the good flame retardant properties of the electrolytes indicate that dual-salt polymer electrolytes are an effective strategy for achieving high safety and long cycle stability of LMBs.

A Rechargeable Solid-State Sodium-Oxygen Battery with Enhanced Energy Efficiency and Cycle Life

Sodium-oxygen (Na-O2) batteries offer a promising path for the advancement of high-energy-density inexpensive storage systems to replace current state of the art Li-based batteries owing to the natural abundance and low-cost Na metal. Despite numerous studies to improve the performance of liquid-based electrolyte Na-O2 batteries, this technology suffers from poor cycle life, electrolyte stability issues, and limited choice of cell design as well as growing safety concerns associated with liquid electrolytes. Recently, solid electrolytes received a great attention to substitute traditional liquid electrolytes used in Na-O2 batteries, due to their ability of improving safety and energy density. However, low ionic conductivity and high impedance in contact with the anode and cathode remain as major challenges for the development suitable solid-state electrolyte for Na-O2 batteries.In addressing these challenges, we recently have established a solid-state Na-O2 battery cell that comprises a highly conductive composite polymer-ceramic solid electrolyte with a conductivity of 0.7 mS/cm. This solid electrolyte works in synergy with vanadium phosphide (VP) nanoparticles, serving as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts at the cathode and Na metal anode for more than 500 reversible charge-discharge cycles at a capacity of 1000 mAh/g, achieving a low polarization gap of approximately 20 mV in the first cycle. Various electrochemical and physicochemical characterization techniques, such as Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), differential electrochemical mass spectrometry (DEMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), were employed to gain insight into the cell chemistry and solid-state electrolyte role in the formation and decomposition of sodium oxides components such as superoxide (NaO2), peroxide (Na2O2). The findings of this study underscore the significance of proper cell component design and possible mechanisms in solid-state Na-O2 battery technologies. This research represents a promising avenue in advancing energy conversion and storage systems, showcasing the potential of solid-state batteries with enhanced safety and performance characteristics.

A new ionic liquid-based electrolyte with both high conductivity and electrochemical stability

Ionic liquids with non-flammability and wide electrochemical window are the promising candidates for the next-generation high-energy lithium metal batteries (LMBs). However, their high viscosity and low ionic conductivity lead to a limited cycling performance, hindering their commercial application. Herein, a new ionic liquid-based electrolyte (ILE) composed of lithium bis(fluorosulfonyl)imide (LiFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI), ethyl methyl carbonate (EMC) and fluorinated ethylene carbonate (FEC) is designed to address this barrier. The new ILE exhibits high conductivity, which is twice that of pure ILE. In addition, FEC that is weakly coordinated to Li+ increases the combination between Li+ and FSI− indirectly, inducing a deeper co-decomposition of FSI− and FEC, thereby leading to a construction of LiF-rich solid electrolyte interphase (SEI). Consequently, Li/Cu battery maintains a higher lithium stripping/plating Coulombic efficiency (CE) of 96.3 % at 250 cycles and Li/LiFePO4 battery reaches a 93.2 % capacity retention at 150 cycles with an average CE of 99.8 %. The designed ILE with both high conductivity and electrochemical stability opens up a new insight for the rational design of electrolytes applied in next-generation LMBs.

Improving electrochemical sodium storage performance and insight into the sodium ion diffusion in the high-pressure polymorph β-V2O5

The high-pressure form of vanadium pentoxide, β-V2O5, possesses promising sodium storage properties, featuring reversible sodium intercalation of one Na+ per formula unit, yielding an appealing capacity of 147 mAh g−1. However, its short cycle life in conventional carbonate-based electrolytes remains a significant drawback. In this work, we demonstrate that using non-carbonate-based electrolytes markedly enhances key electrochemical performances. Additionally, reducing the particle size of β-V2O5 through milling significantly increases the specific capacity, particularly at high current rates. Milled V2O5 maintains a respectable capacity of 73 mAh g−1 at 1 C rate, compared to the negligible capacity observed in non-milled V2O5. The milling process also alters the energy storage mechanism. Interestingly, after milling, sodium diffusion coefficient (DNa+) increased from 1.78 × 10−13 to 1.73 × 10−11 cm2 s−1, likely due to induced near-surface defects. Sodium storage exhibits dominant faradaic behavior at slow current rates, while, at high current rates, capacitive processes predominate. The synergy of improved sodium diffusion and additional capacitive charge storage leads to significantly improved electrochemical performance at high current rates. Furthermore, ionic liquid-based electrolytes promote long-life cycling, advancing this material toward practical application as a cathode in sodium-ion cells.

Enhancing the Cycle Life of Zinc-Iodine Batteries in Ionic Liquid-Based Electrolytes.

Aqueous zinc-iodine (Zn-I2) batteries are gaining significant attention due to their low-cost, high safety and high theoretical capacity. Nevertheless, their long cycle and durability have been hampered due to the use of aqueous media that, over time, lead to Zn dendrite formation, hydrogen evolution reaction, and polyiodide dissolution. Xiao et al. recently reported the addition of an imidazolium-based ionic liquid (IL) to an aqueous electrolyte and found that the IL plays a key role in modifying the solvation of Zn2+ ions in the bulk electrolyte and the inner Helmholtz plane,repelling H2O molecules away from the Zn anode surface. UV/Vis and NMR spectroscopy also indicates a strong interaction between imidazolium cation [EMIM]+ and I3 -, thereby reducing polyiodide shuttling and enhancing the cycle life of the battery. Overall, a capacity decay rate of only 0.01 % per cycle after over 18,000 cycles at 4 A g-1, is observed, making the use of IL additives in aqueous electrolytes highly promising candidates for Zn-I2 batteries.

Thermal Warning and Shut-down of Lithium Metal Batteries Based on Thermoresponsive Electrolytes.

The thermal runaway issue represents a long-standing obstacle that retards large-scale applications of lithium metal batteries. Various approaches to inhibit thermal runaway suffer from some intrinsic drawbacks, either being irreversible or delayed thermal protection. Herein, this work has explored thermo-responsive lower critical solution temperature (LCST) ionic liquid-based electrolytes, which provides reversible overheating protection for batteries with warning and shut-down stages, well corresponding to an initial stage of thermal runaway process. The batteries could function stably below 70°C as a working mode, while demonstrating a warning mode above 80°C with a noticeable reduction in specific capacitance to delay temperature increase of batteries. In terms of 110°C as a critically dangerous temperature, a shut-down mode is designed to minimize the thermal energy releasing as the batteries are barely chargeable and dischargeable. Dynamically growing polymeric particles above LCST contributed to such an intelligent and mild control on specific capacitance. Larger size will occupy larger surfaces of electrodes and close more pores of separators, enabling a gradual suppressing of Li+ transfer and reactions. The present work demonstrated a scientific design of thermoresponsive LCST electrolytes with a superiorly precise and intelligent control of electrochemical performances to achieve self-adapted overheating protections.

Influence of anion structure on Li+ solvation and diffusion in ionic liquid-based electrolyte, and decomposition mechanism of anion

Ionic liquids (ILs) are promising electrolytes for lithium batteries. Particularly, the structure of anions plays a vital role in electrochemical performances. In this work, we chose two asymmetric anions ((fluorosulfonyl)(perfluoroethylsulfonyl)imide (FETI-) and 2,2,2-trifluoro-N-(trifluoromethylsulfonyl)acetamide (TSAC-)) and compared with the symmetric one (bis(trifluoromethanesulfonyl)imide (TFSI-)) to investigate the microcosmic mechanism of the effect of structure on Li+ diffusion through classical molecular dynamics (MD) simulations. We investigated the Li+ solvation structure in electrolytes and found that the asymmetry of anions facilitates the formation of monodentate configuration, but they are not effective in accelerating the Li+ diffusion. On the other hand, we found that the faster Li+ diffusion comes from both the higher diffusion coefficient of anions and the smaller size of Li+ aggregates in electrolytes. In addition, the decomposition mechanism of these anions was investigated by ab initio molecular dynamics (AIMD) simulations. The F directly attached to sulfonyl is unstable, leading to the earlier breaking of the S-F bond compared to S-O and S-N bond, forming early protective components of LiF in solid electrolyte interphase (SEI). This work provides guidance for the design of anions, revealing that the influence of anion structure on Li+ solvation and diffusion in IL-based electrolytes, and decomposition mechanism of anions.

High-performance flexible planner device featuring WS2 electrode and non-aqueous polymeric ionic electrolytes incorporated with ionic liquid and dual redox additives

Introducing redox-active species to enhance redox-activity at electrode–electrolyte interfaces, and designing the rational architecture of flexible supercapacitors comprising high-performance active materials and electrolytes with a wide potential window would be a key strategy to boost energy and power density. Herein, for the first time, we prepared an ionic liquid-based polymer electrolyte (IL/PE) by entrapping ionic liquid N-methyl-N-butyl pyrrolidinium bis (trifluoromethane sulfonyl) imide (P14TFSI)) in a polymer electrolyte Poly (diallyl dimethylammonium bis (trifluoromethane sulfonyl) imide (PDADMATFSI)) and blended with dual redox-additives (potassium iodide, KI and diphenylamine, DPA). The IL/PE with dual redox additives, demonstrates spectacular flexibility, high ionic conductivity (∼23.8 × 10−4 S cm−1), and stability in a wide potential window (∼5.9 V). A symmetrical interdigitated planner device is fabricated using dual redox-active IL/PE and flower-like WS2 electrode material. Benefiting from the synergistic effect of dual redox-active additive, the highest energy density of 47.86 µWh cm−2 at a power density of 3509 µW cm−2, and a high working potential (3 V) with excellent cycling stability upto 20,000 cycles has been achieved.

A Comprehensive Review of Novel Emerging Electrolytes for Supercapacitors: Aqueous and Organic Electrolytes Versus Ionic Liquid-Based Electrolytes

A Comprehensive Review of Novel Emerging Electrolytes for Supercapacitors: Aqueous and Organic Electrolytes Versus Ionic Liquid-Based Electrolytes

The influence of trihaloacetic acids on the hydrogen sorption properties of palladium nanoparticles-modified AB5 alloy in aprotic ionic liquid: Towards ionic liquid-based electrolytes for hydride batteries

Binary mixtures of acetic acid/trihaloacetic acids with aprotic ionic liquid – 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MS]) are used as electrolytes for hydrogen electrosorption measurements. Preliminary studies are performed with palladium limited volume electrode to determine optimum concentration of the acid additives for hydrogen capacity and physicochemical properties of the electrolytes. The results obtained for trichloro- and tribromoacetic acid indicate that their decarboxylation occurs after mixing with [EMIM][MS] and dissolution of palladium is observed in contact with the decomposed electrolyte. Research on hydrogen capacity of palladium nanoparticles-modified AB5-type alloy is performed in mixtures of acetic acid and trifluoroacetic acid of optimum concentration. The best electrochemical performance is demonstrated by 2 M acetic acid/[EMIM][MS] mixture. The determined value of specific capacity of the investigated hydrogen absorbing material reaches 230 mAh g−1 and is close to that previously obtained from aqueous solutions of acids or bases.

Unravelling solvation structure and interfacial mechanism of pyrrolidinium-based ionic liquid electrolytes in potassium-ion batteries

Ionic liquid-based electrolytes (ILEs) show great potential in mitigating the dissolution of organic electrode materials as well as manipulating the interfacial electrochemistry for long lifespan of potassium-ion batteries (PIBs). Herein, KFSI/Pyr13FSI ILEs with varying K+ and Pyr13+ ratios were designed to match a novel organic K-storage anode of p-toluic acid/CMK3 (PTA/CMK3). These ILEs exhibited facilely manipulated solvation structures, resulting into excellent compatibility with K-metal as well as promotion of the generation of robust solid-electrolyte interphase (SEI) for stable K-storage. As a result, the optimized PTA/CMK3||KFSI/Pyr13FSI K-storage system delivered a reversible capacity of 190 mAh/g(composites) alongside high coulomb efficiency of 99.7 % at a current density of 200 mA/g for 600 cycles. This work provides a fresh insight on rational design of ILEs-based advanced PIBs with high energy density and safety.

Ionic liquid-based self-healing gel electrolyte for high-performance lithium metal batteries

The gel electrolytes with self-healing function are being considered as promising replacement for traditional liquid electrolytes in lithium metal batteries due to their excellent battery safety, high energy density and minimum electrolyte damage. However, balancing self-healing, conductivity and mechanical properties remains a challenge for their practical application. Herein, a new ion liquid-based self-healing gel polymer electrolyte (IL-SHGPE) is introduced. The electrolyte was synthesized via UV-induced cross-linking of a polymer containing quadruple hydrogen bond units and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-TFSI) ion liquid. The resultant IL-SHGPE demonstrates exceptional self-healing ability (with 95% healing efficiency within 30 min), excellent thermal stability over a wide temperature range up to 410 °C. It also exhibits impressive mechanical strength with 41.3% elongation and 1.9 MPa tensile stress, room temperature ionic conductivity of 1.29 × 10−3 S/cm, and a wide electrochemical stability window of 5.18V (vs Li/Li+). Lithium metal batteries with this electrolyte showed an initial discharge capacity of 139 mAh g−1 at 1C rate, and a capacity retention of 88.3% after 200 cycles. Therefore, this work provides a significant exploration for balancing self-healing ability, mechanical attributes, and electrochemical performance of lithium batteries, and thus contributing valuable insights towards the development of high-performance self-healing gel electrolytes for lithium metal batteries.

Gel polymer electrolyte-based dual screen-printed electrodes for the headspace quantification of 4-ethylphenol and ethanethiol simultaneously in wines

The identification and correction of negative factors, such as 4-ethylphenol and ethanethiol, is important to comply with food safety regulations and avoid economic losses to wineries. A simple amperometric measurement procedure that facilitates the simultaneous quantification of both compounds in the gas phase has been developed using fullerene and cobalt (II) phthalocyanine-modified dual screen-printed electrodes coated with a room temperature ionic liquid-based gel polymer electrolyte. The replacement of the typical aqueous supporting electrolyte by low-volatility ones improves both operational and storage lifetime. Under the optimum conditions of the experimental variables, Britton Robinson buffer pH 5 and applied potentials of + 0.86 V and + 0.40 V for each working electrode (vs. Ag ref. electrode), reproducibility values of 7.6% (n = 3) for 4-ethylphenol and 6.6% (n = 3) for ethanethiol were obtained, as well as capability of detection values of 23.8 μg/L and decision limits of 1.3 μg/L and 9.2 μg/L (α = β = 0.05), respectively. These dual electrochemical devices have successfully been applied to the headspace detection of both compounds in white and red wines, showing their potential to be routinely used for rapid analysis control in wineries.Graphical

Effects of Ti3C2Tx MXene Addition to a Co Complex/Ionic Liquid-Based Electrolyte on the Photovoltaic Performance of Solar Cells.

Redox mediators comprising I-, Co3+, and Ti3C2Tx MXene were applied to dye-sensitized solar cells (DSCs). In the as-prepared DSCs (I-DSCs), wherein hole conduction occurred via the redox reaction of I-/I3- ions, the power conversion efficiency (PCE) was not altered by the addition of Ti3C2Tx MXene. The I-DSCs were exposed to light to produce Co2+/Co3+-based cells (Co-DSCs), wherein the holes were transferred via the redox reaction of Co2+/Co3+ ions. A PCE of 9.01% was achieved in a Co-DSC with Ti3C2Tx MXene (Ti3C2Tx-Co-DSC), which indicated an improvement from the PCE of a bare Co-DSC without Ti3C2Tx MXene (7.27%). It was also found that the presence of Ti3C2Tx MXene in the redox mediator increased the hole collection, dye regeneration, and electron injection efficiencies of the Ti3C2Tx-Co-DSC, leading to an improvement in both the short-circuit current and the PCE when compared with those of the bare Co-DSC without MXene.

From Molecular Simulations to Experiments: The Recent Development of Room Temperature Ionic Liquid-Based Electrolytes in Electric Double-Layer Capacitors.

Due to the unique properties of room temperature ionic liquids (RTILs), most researchers' interest in RTIL-based electrolytes in electric double-layer capacitors (EDLCs) stems from molecular simulations, which are different from experimental scientific research fields. The knowledge of RTIL-based electrolytes in EDLCs began with a supposition obtained from the results of molecular simulations of molten salts. Furthermore, experiments and simulations were promoted and developed rapidly on this topic. In some instances, the achievements of molecular simulations are ahead of even those obtained from experiments in quantity and quality. Molecular simulations offer more information on the impacts of overscreening, quasicrowding, crowding, and underscreening for RTIL-based electrolytes than experimental studies, which can be helpful in understanding the mechanisms of EDLCs. With the advancement of experimental technology, these effects have been verified by experiments. The simulation prediction of the capacitance curve was in good agreement with the experiment for pure RTILs. For complex systems, such as RTIL-solvent mixtures and RTIL mixture systems, both molecular simulations and experiments have reported that the change in capacitance curves is not monotonous with RTIL concentrations. In addition, there are some phenomena that are difficult to explain in experiments and can be well explained through molecular simulations. Finally, experiments and molecular simulations have maintained synchronous developments in recent years, and this paper discusses their relationship and reflects on their application.

A rechargeable calcium-oxygen battery that operates at room temperature.

Calcium-oxygen (Ca-O2) batteries can theoretically afford high capacity by the reduction of O2 to calcium oxide compounds (CaOx) at low cost1-5. Yet, a rechargeable Ca-O2 battery that operates at room temperature has not been achieved because the CaOx/O2 chemistry typically involves inert discharge products and few electrolytes can accommodate both ahighly reductive Ca metal anode and O2. Here we report a Ca-O2 battery that is rechargeable for 700 cycles at room temperature. Our battery relies on a highly reversible two-electron redox to form chemically reactive calcium peroxide (CaO2) as the discharge product. Using a durable ionic liquid-based electrolyte, this two-electron reaction is enabled by the facilitated Ca plating-stripping in the Ca metal anode at room temperature and improved CaO2/O2 redox in the air cathode. We show the proposed Ca-O2 battery is stable in air and can be made into flexible fibres that are weaved into textile batteries for next-generation wearable systems.

Zwitterionic Materials for Enhanced Battery Electrolytes.

Zwitterions (ZIs), which are molecules bearing an equal number of positive and negative charges and typically possessing large dipole moments, can play an important role in improving the characteristics of a wide variety of novel battery electrolytes. Significant Coulombic interactions among ZI charged groups and any mobile ions present can lead to several beneficial phenomena within electrolytes, such as increased salt dissociation, the formation of ordered pathways for ion transport, and enhanced mechanical robustness. In some cases, ZI additives can also boost electrochemical stability at the electrolyte/electrode interface and enable longer battery cycling. Here, a brief summary of selected key historical and recent advances in the use of ZI materials to enrich the performance of three distinct classes of battery electrolytes is presented. These include: ionic liquid-based, conventional solvent-based, and solid matrix-based (non-ceramic) electrolytes. Exploring a greater chemical diversity of ZI types and electrolyte pairings will likely lead to more discoveries that can empower next-generation battery designs in the years to come.

Theoretical Study on the Electronic Structure of Polymer-in-Salt/Ionic Liquid-Based Biodegradable Gel Polymer Electrolyte

Theoretical Study on the Electronic Structure of Polymer-in-Salt/Ionic Liquid-Based Biodegradable Gel Polymer Electrolyte

Investigating the efficacy of functionalized graphene oxide with polyhedral oligomeric silsesquioxane as an effective additive in sustainable ionic liquid-based electrolytes for dye-sensitized solar cells through experimental and DFT studies

The focus of the study has been on the first-ever use of functionalized graphene oxide with polyhedral oligomeric silsesquioxane (FGO-POSS) as an effective additive to ionic liquid-based electrolytes in dye-sensitized solar cells (DSSCs). The electrolytes consisted of binary ionic liquids (ILs), 1-ethyl-3-methylimidazolium iodide (EMII), and 1-butyl-3-methylimidazolium iodide (BMII). Different concentrations of the efficient additive FGO-POSS, ranging from 0% to 1%, were incorporated into the electrolytes.Under highly controlled conditions, a series of reactions was conducted to synthesize FGO-POSS. By reacting graphene oxide (GO) with L-phenylalanine, initially, GO-L-phenylalanine was obtained. In the next phase, GO-L-Phenylalanine reacted with SSQ-[3-(2-Aminoethyl) amino] propyl-Heptaisobutyl substituted to modify its structure with polyhedral oligomeric silsesquioxane (POSS). The ILs, namely EMII, and BMII, were synthesized using the scientific methodologies detailed in the referenced articles. Furthermore, BMII was functionalized with CuI (BMICuI-2) through a specific procedure.Five types of electrolytes were prepared to be employed in DSSCs using prepared ILs and FGO-POSS, and their results were reported to show the electrical and gelatin features of these types of electrolytes. According to this study's findings, using FGO-POSS as an innovative and efficient additive in ILs-based environmentally sustainable nanocomposite electrolytes in an amount of 0.75 wt% increased the value of the short circuit current density (JSC) from 9.433 mA.cm−2 to 15.592 mA.cm−2, the open circuit voltage (VOC) from 0.738 V to 0.762 V, and the overall efficiency (η) increased from 4.965 to 8.303 %. The FGO-POSS and ILs, EMII, and BMICuI-2 boost electron transport and electrolyte conductivity, resulting in increased JSC, VOC, and η. Results of the density functional theory (DFT) calculation indicated that the adsorption of the FGO-POSS electrolyte additives on the TiO2 electrode surface produces midgap states in the band gap of TiO2, resulting in the reduction of the total bandgap and less barrier electron transfer and a redshift in the adsorption edge and enhancement of DSSCs' efficiency.