Highly Conductive Ionic Liquid Electrolytes for Potassium-Ion Batteries

1. Introduction Lithium secondary batteries have been widely used as power sources for small electronic devices. However, there are still many challenges for the widespread use as large storage batteries, such as the volatility and flammability of the organic-solvent-based electrolytes, and the uneven distribution and scarcity of lithium and cobalt resources.Therefore, we have been developing sodium and potassium-ion secondary batteries using FSA-based ionic liquid (IL) electrolytes (FSA = bis(fluorosulfonyl)amide) because the FSA-based ILs have excellent electrochemical stability and ionic conductivities, and sodium and potassium resources are abundant in the Earth’s crust [1,2].In this study, we focus on FTA-based ILs (FTA = (fluorosulfonyl)(trifluoromethylsulfonyl)amide) as promising electrolytes for alkali metal-ion batteries. The FTA-based ILs have lower melting points and higher thermal stability than the FSA-based ones, which is advantageous for broadening the operating temperature range of batteries [3,4]. The physicochemical properties of M[FTA]–[C4C1pyrr][FTA] ILs (molar fraction x(M[FTA]) = 0.20; M = Li, Na, K, Rb, Cs; C4C1pyrr = N-butyl-N-methylpyrrolidinium) were investigated to discuss the effect of alkali metal-ion species. 2. Experimental All reagents were handled under argon atmosphere. The M[FTA]–[C4C1pyrr][FTA] (x(M[FTA]) = 0.20; M = Li, Na, K, Rb, Cs) ionic liquids were prepared, and their ionic conductivities, viscosities, densities, and electrochemical windows were measured. The electrochemical windows were determined by cyclic voltammetry (CV) measurements using a three-electrode cell. The components of the three-electrode cell were as follows; a copper disk electrode and a glassy carbon disk electrode were used in the negative and positive potential region as the working electrodes, respectively, a platinum mesh electrode was used as the counter electrode, and an Ag+/Ag electrode was used as the reference electrode. 3. Result and discussion Fig. 1 shows the Arrhenius plots of the ionic conductivities for M[FTA]–[C4C1pyrr][FTA] ILs. The order of the ionic conductivities (mS cm−1) is Na(1.7) < Li(2.0) < K(2.2) < Rb(2.3) < Cs(2.6) at 298 K. In terms of ion size, the smallest Li+ is considered to be the most favorable for the ionic conduction. However, its ionic conductivity is lower than those of K+, Rb+, and Cs+-based systems. One possible explanation is that the higher charge densities of Li+ and Na+ lead to the strong ion interaction with FTA−, resulting in the lower ion mobilities of alkali-metal ion complexes. We also measured their viscosities and densities of the FTA-based ILs at 273–368 K and constructed a Walden plot, which suggested that all the FTA-based ILs do not have a special ion conduction mechanism such as the Grotthuss mechanism.Fig. 2 summarizes the results of the CV measurements for M[FTA]–[C4C1pyrr][FTA] ILs. The order of their electrochemical windows (V) is Na(5.33) < Li(5.45) < K(5.58) < Rb(5.64) < Cs(5.74) at 298 K. The redox peaks were observed in the negative potential regions for all the electrolytes, which corresponds to the deposition and dissolution of alkali metals. On the other hand, irreversible oxidation currents were observed in the positive potential region for all the electrolytes. Since there was little difference in the anode limits for all the electrolytes, these oxidation currents are considered to be the decomposition of FTA− anions [4]. The trends of the physicochemical properties obtained in this study are very similar to those for FSA-based ionic liquids reported by our group [1]. R eferences [1] T. Yamamoto, K. Matsumoto, R. Hagiwara, T. Nohira, J. Phys. Chem. C, 121, 18450 (2017).[2] R. Hagiwara, K. Matsumoto, J. Hwang, T. Nohira, Chem. Rec., 18, 1 (2018).[3] K. Kubota, T. Nohira, R. Hagiwara, H. Matsumoto, Chem. Lett., 39, 1303 (2010).[4] K. Kubota, H. Matsumoto, J. Phys. Chem. C, 117, 18829 (2013). Figure 1

1. Introduction Most of the non-renewable energy resources such as coal and petroleum being used all over the world, are causing serious problems of climate change. Thus, the need of the hour is to reduce the usage of these resources and increase that of renewable ones, which is realized by bringing energy storage devices into picture. Batteries are the potential candidates of energy storage devices. The development of lithium-ion battery (LIB) revolutionized the electronic industry and has impacted the vehicle industry [1]. Although LIBs are predominant choices for many applications in day to day life, the depletion of cobalt and lithium resources is a matter of growing concern. In order to mitigate the concern, we need to find alternatives for LIBs. One of the promising ways to fulfill such demands is to analyze the practical use of other alkali metal-ion batteries, such as Na-ion battery (NIB) and K-ion battery (KIB) [2, 3].In the present paper, we have conducted comparative studies on graphite (Gr) and hard carbon (HC) negative electrodes for alkali metal-ion batteries, i.e., LIBs, NiBs and KIBs, using FSA-based ionic liquids (FSA: bis(fluorosulfonyl)amide). These carbon materials are the most common intercalation-type electrode materials. They are also cheap, easy to prepare, and environmental benign. Moreover, the organic solvent-based electrolytes that are primarily used for batteries are inherently very volatile, flammable and unsafe to use, whereas the ionic liquid electrolytes used in the present study are non-volatile and safe to use. We have focused on the FSA-based ionic liquids because they possess high electrochemical and thermal stability, which is advantageous for the rechargeable batteries operating at higher temperatures as well [4–6]. 2. Experimental The working electrodes (Gr and HC) coated onto a copper foil and a separator were vacuum impregnated with the electrolyte at 333 K overnight before assembling the cells. The mass loading of active materials for all the electrodes was around 3.8–4.2 mg cm−2. The electrolytes used were M[FSA] (M = Li, Na, K)–[C3C1pyrr][FSA] (C3C1pyrr: N-methyl-N-propylpyrrolidinium) ionic liquids. Molar fraction of M[FSA], x(M[FSA]), was 0.20 in all cases of LIB, NIB and KIB. A glass fiber filter (Whatman GF/A, 260 μm t ) was used as the separator, and metallic lithium, sodium and potassium were used as the counter electrodes for LIB, NIB and KIB, respectively. CR2032-type coin cells were fabricated in an argon filled glovebox and the operating temperature was set at 298–333 K. 3. Results and discussion The charge–discharge tests were performed at current rates from 0.1C to 2C (1C = 372 mA g−1) for graphite (Gr) electrodes and 20 mA g−1 to 200 mA g−1 for hard carbon (HC) electrodes.As shown in Fig. 1a, for Li/Gr cells at 333 K, we obtained a discharging capacity of 337 mAh (g-Gr)−1 at 0.2C (74.4 mA g−1) current rate. The cell exhibited good cycleability, retaining a discharging capacity of 348 mAh (g-Gr)‒1 and 99.9% coulombic efficiency even after 4 cycles. For the Na/Gr cell (Fig. 1c), a discharging capacity of only 3 mAh (g-Gr)−1 was obtained, being consistent with the well-known fact that graphite does not form intercalation compounds with sodium.For the Li/HC cell (Fig. 1b), the initial charging and discharging capacities were 447 and 361 mAh (g-HC)−1, respectively, at 20 mA (g-HC)−1 current rate. The coulombic efficiency was 80% for the first cycle. A discharging capacity of 330 mAh (g-HC)−1 was obtained after 5 cycles at 20 mA (g-HC)−1. For the Na/HC cell, as shown in Fig. 1d, the initial charging and discharging capacities were 305 and 263 mAh (g-HC)−1, respectively, at 20 mA (g-HC)−1. The coulombic efficiency was 86% for the first cycle and more than 99% for the rest of the cycles.In the presentation, more detailed results including the ones of KIB will be given. Acknowledgement A part of this study was supported by JSPS KAKENHI grant (JP18K14320). Graphite powder was supplied from SEC Carbon Ltd.

The development of new materials for secondary batteries is nowadays one of the most active fields in the international scientific panorama [1].The state of the art for liquid electrolytes in a lithium-ion cell is typically a mixture of organic carbonates such as ethylene carbonate (EC) or dimethyl carbonate (DMC). The mixture ratio varies depending upon the desired cell properties. These solvents contain solvated lithium ions. The latter are provided by lithium salts, most commonly lithium hexafluorophosphate (LiPF6)[2]. Despite the high conductivity of these electrolytes (s >10-3 S·cm-1 at RT), important drawbacks are associated with the volatility and flammability of liquid solvents and the chemical instability of the LiPF6 salt. The latter undergoes hydrolysis in the presence of water traces, releasing fluoride anions. [3]Ionic liquids (ILs) are salts with melting temperatures lower than 100°C. When they are liquid at room temperature, ILs are classified as room temperature ILs (RTILs). Some typical properties of ILs are: a) a low volatility, a high thermal stability and a negligible flammability; b) a high ion density and conductivity; c) a wide electrochemical stability window; and d) a simple synthesis, carried out by choosing the cation and anion which best comply with the requirements of the intended application. These features make ILs very suitable as solvents in electrolytes for Li batteries[4].Recently, a class of solid-state single-ion conducting materials based on lithiated fluorinated-TiO2 (LiFT) was proposed, which demonstrated its applicability as a nanofiller to obtain nanocomposite polymer electrolytes [5,6]. LiFT consists of fluorinated anatase nanoparticles that are directly surface-functionalized with Li+ through an innovative one-step reaction with molten metallic lithium[7]. The conductivity of LiFT is due to Li+hopping processes between coordination sites present at the nanoparticle grain boundaries. These latter events take place in a very effective way.The use of LiFT nanoparticles as the source of Li+ ions and ILs as the plasticizing agents allowed us to obtain innovative composite electrolytes for application in lithium batteries with a high thermal stability and conductivity. Indeed, the use of imidazolium ILs based on TFSI- and BF4 - anions allowed us to investigate the different ability of these anions to coordinate and dissociate the Li+cations present on the surface of LiFT nanoparticles. For these reasons it has to be highlighted that no conventional Li salts are used in the electrolytes here proposed.In this report, composite electrolytes based on LiFT nanopowder, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI) ILs are proposed. In details, LiFT nanopowder is doped with a known amount of both ILs to obtain two types of electrolytes with formula LiFT/EMImTFSI0.118 and LiFT/EMImBF4 0.200. The resulting electrolytes contain around 25% wt of ILs and show a powder-like consistence.The correlation between structure, thermal properties and conductivity mechanisms of the resulting LiFT/EMImTFSI0.118 and LiFT/EMImBF4 0.200electrolytes is investigated by a variety of techniques: (a) FT-MIR and FIR at different temperatures; (b) Differential Scanning Calorimetry (DSC); (c) Thermogravimetric Analysis (TGA); and (d) Broadband Electrical Spectroscopy (BES).The materials are thermally stable up to 250°C and their conductivities at 30 and 130°C are, respectively, of 1.2x10-2 cm-1 and 4.1x10-2 Scm-1 for LiFT/EMImTFSI0.118 and 1.7x10-3 Scm-1 and 1.7x10-2 Scm-1, for LiFT/EMImBF4 0.200. Finally, the performance of the proposed materials, tested in operating CR2032 coin cells by galvanostatic cycling in a Li4Ti5O12/{LiFT/EMImTFSI0.118}/LiCoO2configuration is shown in Figure 1. Figure 1 Discharge profiles (inset) and capacity vs. cycle number for a Li4Ti5O12/ {LiFT/EMImTFSI0.118}/LiCoO2, CR2032, coin cell (discharge plotted as negative current).

The physicochemical and electrochemical properties of the binary ionic liquid, K[FSA]–[C3C1pyrr][FSA] (FSA = bis(fluorosulfonyl)amide; C3C1pyrr = N-methyl-N-propylpyrrolidinium), were investigated at 253–393 K, with the aim of developing a new electrolyte for potassium-ion batteries (K-ion batteries; KIBs). A phase diagram was constructed from the results of differential scanning calorimetry measurements and revealed that the melting point of this ionic liquid is below room temperature for compositions of x(K[FSA]) = 0–0.25 (x(K[FSA]) = molar fraction of K[FSA]). The viscosity, ionic conductivity, and density were measured for x(K[FSA]) = 0–0.25. The ionic conductivity when x(K[FSA]) = 0.20 was 4.8 mS cm–1 at 298 K, which is higher than that for the equivalent sodium and lithium ionic liquids. Cyclic voltammetry measurements of M[FSA]–[C3C1pyrr][FSA] ionic liquids (x(M[FSA]) = 0.20; M = K, Na, or Li) indicated that potassium metal deposition/dissolution occurs at a more negative potential than that for li...

Ionic liquids (ILs) are salts possessing many properties that make them attractive for use in a wide range of applications including batteries. One of the biggest drawbacks of ILs is that they tend to be more viscous than conventional solvents, which means low ionic conductivity when used as electrolytes in batteries. One effective way to lower the viscosities is to mix ILs with low viscosity additives such as molecular solvents. An obvious disadvantage of mixing molecular solvents with ILs is that the extremely low volatility of the IL is compromised by the finite vapor pressure of the diluent. One strategy to overcome this is to mix ILs with molecular solvents that are themselves of very low volatility. One such class of compounds are the glymes, which are oligoethers having a CH3O-(CH2CH2O)n-CH3 structure. In addition to having low volatility, glymes are effective at dissociating salts because of the electron donating nature of their ether oxygen groups. They also tend to have high thermal and electrochemical stability, which has led many groups to investigate mixing glymes with alkali metal salts (most commonly Li+ [NTf2]) for use as electrolytes in batteries. The alkali metal cation tends to coordinate with the oxygen atoms of the glyme, which can significantly lower the melting point of the salt. Such systems usually retain the attractive properties of pure ILs but the transport properties are improved. They are considered a new class of ILs and have been termed “solvate ILs”. Tetraethylene glycol dimethyl ether (tetraglyme or G4) is a particularly promising glyme. While there are many studies devoted to the properties of Li-based solvate ILs, much less work has been done investigating the properties of mixtures containing glymes and more conventional ionic liquids. In the current work, the density and viscosity of the IL [C6mim][NTf2]) and its mixtures with tetraglyme were measured at different temperatures and concentrations. Molecular dynamics (MD) simulations were also carried out on the mixtures in order to compute the density, self-diffusivity, viscosity, ideal ionic conductivity and liquid structure. We find that both the density and viscosity drop with increasing temperature and G4 concentration. Detailed analysis of the simulation results suggests that G4 preferentially solvates the cations, thereby weakening the interactions with the anions and resulting in faster dynamics, particularly for the anions. Such behavior was previously observed in solvate ionic liquids. Based on the simulation results of a model G4 system, it was further revealed that the localized negative charges on the oxygen atoms of G4 are primarily responsible for the preferential solvation of cations. If G4 (or a similar solvent) instead had large localized positive charges, it would tend to preferentially solvate the anions, resulting in increased cation mobility. This suggests a strategy for selecting molecular solvents that will selectively enhance cation dynamics.

Lithium batteries are the most attractive candidate to replace the traditional energy resources due to their high working voltage, high specific energy and long cycle life [1,2]. However, the widely use have been limited by their safety issues, especially under the condition of abusing or overcharging. In order to solve this issue, it is significant to screen a safe material as lithium batteries electrolyte.Room temperature ionic liquids (RTILs) have aroused much attention for use in lithium batteries, owing to their low volatility, inflammability, wide electrochemical window and high ionic conductivity [3]. Particularly, their excellent thermal stability makes them key to solve the safety issues of lithium batteries at high temperatures and their physicochemical properties can be tuned by introducing functionalized groups onto the cation or anion of RTILs. The functionalized task-special ionic liquids can reduce the viscosity and enhance their ionic conductivity of RTILs. In this study, a piperidinium-based ionic liquid, N-methyl-N-methoxycarbonylpiperidinium bis(trifluoromethanesulfonyl)imide ([MMOCPip][TFSI]), was synthesized by anion exchange reaction and used as an additive to electrolyte of Li-ion battery. The electrochemical performance of the electrolytes had been evaluated by electrochemical tests, such as the line sweep voltammetry, cyclic voltammetry and impedance spectroscopy.The N-methyl-N-methoxycarbonylpiperidinium bis(trifluoromethanesulfonyl)imide ([MMOCPip][TFSI]) ionic liquid was prepared by mixing equimolar N-methyl-N-methoxycarbonylpiperidinium bromide ([MMOCPip][Br]) and bis(trifluoromethanesulfonyl)imide lithium at room temperature in deionized water and by stirring for several hours until a hydrophobic [MMOCPip][TFSI] layer was formed below the water phase [4]. The ionic conductivity of [MMOCPip][TFSI] was 0.77 mS·cm-1 (25℃) and 2.41 mS·cm-1 (60℃), however, after adding 0.1 M LiTFSI, the ionic conductivity decreased to 0.51 mS·cm-1 (25℃) and 1.85 mS·cm-1 (60℃), respectively. The electrochemical window was 0.5 V~5.8 V (vs. Li+/Li), which was enough widely that could be used as common electrode material. The Li-ion transference number of ionic Liquid electrolyte containing 0.1 M LiTFSI was 0.56. The battery tests indicated that the [MMOCPip][TFSI] obviously improved the cyclability of the LiFePO4 cell. For the Li/ LiFePO4 half-cells, after 20 cycles at room temperature at 0.1 C, the discharge capacity was 109.7 mAh·g-1 with 98.7% capacity retention in the [MMOCPip][TFSI]/0.1 M LiTFSI electrolyte. The good electrochemical performance demonstrated that the [MMOCPip][TFSI] could be used as electrolyte additive for lithium batteries. Keywords: Ionic liquid; Li-ion battery; Ionic conductivity; Transference number Reference: [1] Wongittharoma N, Wang CH, Wang YC, Fey GTK, Li HY, Wu TY, Lee TC, Chang JK (2014). Charge-storage performance of Li/LiFePO4 cells with additive incorporated ionic liquid electrolytes at various temperatures. J Power Sources. 260: 268–275.[2] Yang J, Zhou XY, Zou YL, Tang JJ (2011). A hierarchical porous carbon material for high power, lithium ion batteries. Electrochim Acta. 56: 8576–8581.[3] Pandian S, Raju SG., Hariharan KS, Kolake SM, Park DH, Lee MJ (2015). Functionalized ionic liquids as electrolytes for lithium-ion batteries. J Power Sources. 286: 204-209. [4] Yang PX, Cui WY, Li LB, Liu L, An MZ (2012). Characterization and properties of ternary P(VdF-HFP)-LiTFSI-EMITFSI ionic liquid polymer electrolytes. Solid State Sciences. 14(5), 598–606. Figure 1

Potassium-ion batteries (PIBs) are expected to be one of the next-generation rechargeable battery system due to the abundance and cost-effectiveness of potassium resources. Achieving high energy density in PIBs requires electrolytes with a wide electrochemical window that remain stable at high operating voltages. While molten salt electrolytes are known for their low flammability and high electrochemical stability, their high melting points limit their operational range to high temperatures. Therefore, lowering the melting point of molten salt electrolytes is essential for enabling operation over a broader temperature range. Recently, potassium bis(fluorosulfonyl)amide (KFSA) and potassium N,N-(fluorosulfonyl)(trifluoromethylsulfonyl)amide (KFTA) have emerged as promising candidates due to their relatively low melting points and electrochemical stability. A binary mixture of KFSA and KFTA with the specific composition of K[(FSA)0.55(FTA)0.45] has been reported to exhibit a low eutectic temperature of 340 K.1 In this study, we propose low-melting point potassium salts with a single K+ cation, to realize melting point reduction induced by high entropy systems. We explore the optimal compositions of low-melting-point potassium mixed salts and successfully fabricate a potassium-ion polymer-in-salt electrolyte (PPISE) by incorporating the potassium mixed salt in crosslinked poly(ethylene oxide-co-propylene oxide) (P(EO/PO).2 Furthermore, we characterize the thermal and electrochemical properties of PPISE.All preparations of potassium mixed salts and solid polymer electrolytes (SPEs) were conducted in an Ar-filled glovebox. The potassium mixed salts were prepared by mixing KFSA and KFTA in predetermined proportions with the low-melting composition of the binary potassium salts, K[(FSA)0.55(FTA)0.45].1 In addition, ternary mixed salts, K[(FSA) x (FTA) y (TFSA) z ] (x + y + z = 1), were prepared by adding KTFSA to K[(FSA)0.55(FTA)0.45]. SPEs were prepared by dissolving the mixed salt, P(EO/PO) (EO:PO=8:2), and DMPA as a photoinitiator in acetonitrile to obtain a homogeneous solution, followed by vacuum drying. The resulting solution was then exposed to UV irradiation for 5 min for photo-crosslinking reaction.2 The samples were subsequently sealed in stainless-steel (SUS) pressure pans and characterized using differential scanning calorimetry (DSC). The ionic conductivity (σ) was evaluated between 283 K and 363 K using AC impedance spectroscopy with stainless steel electrode symmetrical cells. Figure 1 shows the DSC profiles of the individual potassium salts and K[(FSA)0.46(FTA)0.37(TFSA)0.17]. The samples were cooled from 303 K to 213 K and then heated at a scan rate of 5 K min-1. All the salts exhibited a thermal transition corresponding to the glass transition in the temperature range of 250 K to 290 K. The melting points (T m) of KFSA, KFTA, and KTFSA were observed at 379 K, 376 K, and 474 K, respectively. In contrast, K[(FSA)0.46(FTA)0.37(TFSA)0.17] exhibited the lowest melting point (322 K) among the prepared mixed salts. This significant reduction in T m is attributed to the increase in entropy induced by the multicomponent nature of the salt mixture.3 Figure 2 shows the temperature dependence of σ for each potassium mixed salts. The σ value at 363 K is approximately 3.0 m S cm-1, which is comparable to that of conventional organic electrolytes at room temperature.4 Although the σ of potassium mixed salts slightly decreases with increasing KTFSA composition, σ measurements were still feasible at lower temperatures compared to K[(FSA)0.55(FTA)0.45], owing to the stronger supercooling nature of ternary potassium mixed salts. Figure 3 shows the glass transition temperature (T g) for the prepared SPEs as a function of potassium salt weight percentage. T g increases with potassium salt concentration up to 60 wt%. Beyond this concentration, T g decreases, likely due to the saturation of K+–O (ether oxygen) interactions as potassium salt content increases. This behavior suggests that the maximum T g values mark the boundary between salt-in-polymer and polymer-in-salt compositions.5 Figure 4 shows the σ of SPEs for both ternary and binary potassium salt systems as a function of potassium salt weight percentage. As the potassium salt concentration increases, the number of mobile carrier potassium ion rises, leading to an increase in σ, with a maximum at 20 wt%. However, σ reached a minimum at 50 wt% due to strong ion-polymer interactions. Upon further increasing the potassium salt concentration, σ increases again. These results support that salt-in-polymer to polymer-in-salt electrolyte transition occurred by incorporating low T m ionic liquids into polymeric phase, which was characterized by the T g maximum and the σ minimum.[1] H. Yamamoto, et al., J. Phys. Chem. B, 124, 6341-6347, (2020).[2] M. Kono, et al., J. Electrochem. Soc., 146, 1626-1632 (1999).[3] K. Nishikawa, J. Vac. Soc. Jpn. 56, 43-46, (2013).[4] Y. Yamada, Electrochemistry, 82, 1085-1090, (2014).[5] C. A. Angell, et al., Nature, 362, 137-139, (1993). Figure 1

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

Currently the main application of lithium ion batteries is in portable electronics, but new emerging applications such as electric cars require lower cost, improved cycle life, sustainability, safety and energy density.The ambition of Si-DRIVE European project is proposing next-generation batteries for electric cars built in Europe, designed to ensure recycling above 50%. Si-Drive battery will contain a Silicon anode, which has a high specific capacity, and a high voltage cathode without cobalt to reduce the cost and improve sustainability.As an alternative to conventional organic solvents, ionic liquids have been widely investigated over the years, due to their excellent properties in terms of safety and stability.The 1st generation of electrolytes for Si-Drive includes selected ionic liquids with high ionic conductivity and wide electrochemical stability. The 2nd generation of electrolytes combines the ionic liquids and the precursors of the polymer matrix in the formulation, in order to obtain crosslinked self-standing flexible films. The addition of ceramic super lithium ion conductors to obtain composite polymer electrolytes is also envisaged to improve the electrochemical stability window of the electrolyte.Here we present several different polymer electrolytes and semi interpenetrating polymer networks encompassing ionic liquids and ceramic materials having ionic conductivity > 10 mS/cm at 20 °C, which can be in situ-deposited and crosslinked on top of the electrodes, and combined to form bi-layered electrolyte membranes to tune the compatibility with the electrode materials. The cycling performance with different positive and negative electrodes at ambient temperature is also demonstrated. Acknowledgements: The Si-DRIVE project has received funding from the European Union’s Horizon 2020 Research&Innovation programme, under Grant Agreement 814464. References J.-Y. Hwang, S.-T. Myung, Y.-K. Sun, Chem. Soc. Rev. 46, 3529-3614 (2017)M. Falco, C. Simari, C. Ferrara, J.R. Nair, G. Meligrana, F. Bella, I. Nicotera, P. Mustarelli, M. Winter, C. Gerbaldi, Langmuir 35, 8210-8219 (2019)M. Falco, L. Castro, J.R. Nair, F. Bella, F. Bardé, G. Meligrana, C. Gerbaldi, ACS Appl. Energy Mater. 2, 1600-1607 (2019)M. Falco et al., Electrochem. Commun. 118 106807 (2020)S. Saffirio, M. Falco, G.B. Appetecchi, F. Smeacetto, C. Gerbaldi, Journal of the European Ceramic Society, 42(3), 1023-1032 (2022).

Significant scientific and economic challenges are presented by developing battery systems with increased energy storage capacity. Geopolitical issues might pose supply chain risks for lithium (Li)-ion batteries, which are frequently used in portable electronics. As an alternative, sodium-ion batteries (NIBs), have drawn attention from researchers all over the world due to the perspective of being lower cost systems[1]. In comparison to lithium-ion batteries, solid-state sodium-ion batteries (SSSBs) promise as a safe, scalable, and environmentally friendly alternative. For the production of robust and adaptable SSSBs, the development of highly conductive, electrochemically stable, and chemically stable solid electrolytes (SEs) is essential [2]. With greater durability, adaptability, and safety, solid-state batteries with inorganic solid electrolytes are being heavily investigated as safer and perhaps more energy-dense alternatives to liquid electrolyte cells.Sulfides solid electrolytes have been extensively investigated due to their mechanical softness and high ionic conductivity. However, the electrochemical oxidation stability of those materials are as low as 2 V (vs. Na+/Na)[3]. Alternatively, the excellent ion conductivities and stability at high potentials have made halide compounds, intriguing candidates for solid electrolytes in batteries. These compounds offer fast ion transport, good stability at highly oxidative potentials, and are easily processed. A wide range of chemistries, such as A3MX6 (A = Li, Na; M = Sc, In, Y, Yb, Er, Hf, Ho, Dy, Al, Zr; X = F, Cl, Br, I), have been synthesized with tunable properties and the characterizations of those materials shows relevant electrochemical proprieties [2].In our work, we investigate different Na-based chloride compounds by Density Functional Theory (DFT). We expand beyond the reported compositions to consider possible cation-substituted compounds. Here, we report on the structures, ionic conduction pathways and ionic conductivity (computed by molecular dynamics methods) expected for such compounds. In the next months, we will also evaluate the compounds´ chemical and electrochemical stability. Our work moves us one step closer towards the development of stable and highly conductive solid electrolytes for Na-based solid-state batteries.References :[1] J. Mater. Chem. A, 2021,9, 281-292[2]J. Mater. Chem. A, 2022,10, 21565-21578[3] ACS Energy Lett. 2022, 7, 10, 3293–3301

Ionic liquids (ILs) are salts consisting of organic cations and inorganic/organic anions having melting transitions lower than 100°C. They hold promise as engineered materials in a variety of modern fields. They are used as green solvents or catalysts for chemical reactions, biocatalysts, biopolymers processing, active pharmaceutical ingradients in medicine, even as electrolytes for batteries. For batteries applications, ionic liquids must have high ionic conductivity, but most of the ionic liquids (monocationic) have low conductivities. To address this limitation, we describe in this chapter dicationic ionic liquids based on extended viologens. The colossal conductivities, σdc ~ 10−1.5·S cm1 of new diatonic ionic liquids in the same range of benchmark materials/electrolytes applied in fuel cells and batteries is reported. The relatively new class of ionic liquids consist of extended viologen bistriflimides containing oligoethyleneoxy groups were prepared via Zincke reaction under mild conditions and are excellent candidates as components in devices for energy conversion and storage applications. The synthesis and ionic conductivities of other ionic liquids and dicationic organic salts will be contrasted with dicationic ionic liquids in this chapter.

Current electrolytes for lithium batteries are usually composed of at least two chemical compounds, an organic solvent such as a cyclic carbonate and a lithium salt such as LiPF6. Here, the concept of using a single‐component electrolyte is demonstrated in lithium batteries based on new lithium borate ionic liquids at room temperature. The design concept of this class of lithium ionic liquids (LiILs) is based on an asymmetrically substituted central tetracoordinate boron atom with oligoethylene glycol groups, fluorinated electron‐attracting groups, and one alkane group. The optimized borateLi+ LiILs show a high ionic conductivity value of &gt;10−4 S cm−1 at 25 °C, high lithium transference numbers ( = 0.4 – 0.5) and electrochemical stability (&gt;4 V). Some of the LiILs present high compatibility with lithium‐metal electrodes showing stable polarization profiles in platting/stripping tests. The selected LiIL is investigated as single‐component electrolytes in lithium‐metal battery cells showing discharge capacity values in Li0/LiIL/lithium–iron phosphate and Li0/LiIL/lithium titanate cells of 124 and 75 mAh g−1, respectively, at a C‐rate of 0.2 C and 65 °C with low‐capacity loss.

There is increasing interest in ionic liquid electrolytes for battery applications due to their potential as safer alternatives to conventional liquid electrolytes. By carefully selecting cations and anions, the physicochemical properties of these salts can be optimised. However, investigation of new cations and anions is still required to achieve the desired electrolyte properties such as high conductivity, electrochemical stability and low corrosivity. Thus, here a new series of room temperature ionic liquids (RTILs) and an organic ionic plastic crystal (OIPC) were synthesized and characterized based on N−ethyl−N−methylpyrrolidinium ([C2mpyr]+) and N−ethyl−N−methyloxazolidinium ([C2moxa]+) cations, paired with 4,5‐dicyano‐2‐(trifluoromethyl)imidazolide ([TDI]−) and 4,5‐dicyano‐2‐(pentafluoroethyl)imidazolide ([PDI]−) anions, forming [C2mpyr][TDI] (OIPC), [C2mpyr][PDI] (IL), [C2moxa][TDI] (IL), and [C2moxa][PDI] (IL). Thermal properties were analysed using DSC and TGA. The plastic phase of the OIPC [C2mpyr][TDI] is wide and spans most electrolyte application temperatures, extending from −40 to 56 °C. All salts exhibit thermal stability above 200 °C. The temperature dependence of the transport properties (viscosity, ionic conductivity, self‐diffusion coefficient) were measured and fitted by the Vogel‐Fulcher‐Tamman (VFT) equation, and the ionicity of the ILs is reported. The electrochemical stability windows of the salts were analysed by CV, and the [C2mpyr]+ cation‐based ILs showed the widest window of ~5 V.

In the present study, we report a preparation of a new category of gel polymer electrolytes by immobilizing various compositions of lithium nonafluoro-1-butanesulfonate (LiNfO) salt and less viscous 1-ethyl-3-methylimidazolium nonafluoro-1-butanesulfonate (EMImNfO) ionic liquid in polyvinylidenefluoride-co-hexafluoropropylene (PVdF-co-HFP) matrix for their application in lithium ion batteries. Our study reveals that composition with 80% EMImNfO-LiNfO + 20% PVdF-co-HFP composition has the highest ionic conductivity of 10−2 S cm−1. The performance characteristics of highly conducting ionic liquid incorporated gel polymer electrolyte (ILGPE) is evaluated by using different electrochemical techniques such as chronoamperometry, cyclic voltammetry, and lithium compatibility test. ILGPEs exhibit excellent properties and will facilitate its use as a potential separator for lithium ion batteries.

The insatiable demand for clean, efficient energy storage solutions drives the relentless pursuit of next-generation batteries. Conventional lithium-ion batteries, while dominant, face limitations in energy density, safety, and compatibility with certain electrode materials. Ionic liquids (ILs) emerge as a promising class of electrolytes to overcome these hurdles and propel battery technology forward. ILs are salts consisting of organic cations and inorganic/organic anions having melting transitions lower than 100°C. They are an important class of components used as electrolytes for batteries. High ionic conductivity is crucial for battery applications, but traditional ionic liquids (ILs) and monocationic ionic liquid crystals (ILCs) often fall short. This chapter explores a promising alternative: dicationic ionic liquids (DILs) and dicationic liquid crystals (DILCs) based on extended viologens. These materials exhibit remarkably high ionic conductivities (σdc ≈ 10–1.5 S cm−1), comparable to benchmark electrolytes used in fuel cells and batteries. We report the synthesis of a novel class of DILs and DILCs using a Zincke reaction under mild conditions. These materials feature extended viologen bistriflimides with oligoethyleneoxy groups (DILs) or bistosylates (DILCs). Their excellent ionic conductivity makes them ideal candidates for energy conversion and storage applications. The chapter delves into the detailed synthesis process and the impressive conductivity properties of both DILs and DILCs.