Ternary Electrolyte Research Articles

Polymer‐Induced Inversion of the Li+ Drift Direction in Ionic Liquid‐Based Ternary Polymer Electrolytes

AbstractWhile salt‐in‐ionic liquid (IL) electrolytes provide a promising alternative to organic electrolytes, they suffer from large ionic clusters impeding lithium ion transport. Here, a lithium‐coordinating polymer is added and the transition from salt‐in‐IL to IL‐based ternary polymer gel electrolytes is followed, investigating the influence of the composition on Li transport mechanisms. The electrolyte is composed of the salt lithium bis(trifluoromethanesulfonyl)amide (LiTFSA), the IL 1‐butyl‐1‐methylpyrrolidinium (Pyr14) TFSA, and a variable amount of poly(ethylene oxide) (PEO). Impedance spectroscopy, multinuclear (1H, 7Li, and 19F) diffusion NMR and electrophoretic NMR (eNMR) yield electrophoretic mobilities, transference numbers, partial conductivities, and effective charges of all ionic species. As the polymer fraction increases, the lithium ion drift direction is inverted. The sign reversal of Li+ mobility and transference number occurs at the optimum coordination of 5–6 ethylene oxide units per Li+ ion. The dominant Li+ transport mechanism shifts from a vehicular transport via anionic clusters to chain‐dominated transport mechanisms. It is concluded that the lithium transport properties of IL‐based electrolytes can be vastly improved by the addition of PEO. Tuning the composition of the ternary electrolyte reveals optimal Li+ transport properties at moderately high polymer contents as well as high salt concentrations.

Growing 3D-nanostructured carbon allotropes from CO2 at room temperature under the dynamic CO2 electrochemical reduction environment

Synthesis of nanostructured carbon allotropes using CO2 as a cheap carbon source is challenging and usually limited by high temperature activation. Herein, formation of 3D nanostructured carbon allotropes including nano-graphene and single crystalline nanodiamond films is feasible at room temperature on various single crystal metals (e.g., Bi, Ag, Zn, and Co) that were formed under the dynamic CO2 electrochemical reduction reaction environment at relatively low applied potential (−1.1 to −1.6 V vs. Ag/AgCl). The nanocrystalline carbon was obtained as the major products from CO2 (≥96% selectivity, ∼1 μm thickness) without any liquid products. Upon applying the negative potential, nanoclustering of the self-limiting ultrathin metal oxide layers of metal particles on the highly conductive substrate could lead to formation of negatively charged metal clusters, which were well stabilized by the ternary electrolyte system containing [BMIm]+[BF4]-/propylene carbonate/water. This system allows the reduction of CO2 into single atoms C∗ and the subsequently electrocrystallization of C∗ into carbon allotropes on the crystallographic planes of the single crystal metals formed as the building blocks. The CO2-derived Ag–C/epoxy composites show promising thermal conductivity. The results present a breakthrough advancement in the growth of nanostructured carbon allotropes from CO2 by the viable negative CO2 emission approach.

Low Temperature Performance of Solid Electrochemical Capacitors: Effects of Electrolytes Additives and Electrode Design

Solid-state, thin, and flexible electrochemical capacitors (ECs) can provide energy storage for next-generation wearable electronics such as smart textiles and medical sensors. One of the enablers for high performance and safe electrical double layer capacitors ECs is neutral pH polymer electrolytes due to their wide operating potentials, good ionic conductivity and benign chemical nature [1-3]. Nonetheless, the operation temperature is often limited to above the freezing point of water. For example, a polymer electrolyte based on Na2SO4 ion conductor and polyacrylamide (PAM) host has shown a promising performance at ambient (good shelf-life >30 days and wide 1.8 V window with activated carbon [4]), but its performance degraded drastically at sub-zero conditions [5]. Furthermore, it is of practical importance to understand the effect of high surface area porous carbon materials (e.g. carbon nanotube (CNT) [6-7] or activated carbon (AC) [7-9]) on solid EC at low temperatures, which has not been extensively characterized. To ensure robustness of EC devices operating under winter/sub-arctic and outer space conditions, it is necessary to develop proper polymer electrolytes and the right match of electrode/electrolyte for low temperature ECs.In this study, the performances of solid EC cells constructed with carbon electrodes and Na2SO4-PAM-based electrolytes were assessed at ambient and low temperatures. The objectives were to (i) improve the performance of Na2SO4-PAM electrolytes using anti-icing additives and (ii) elucidate the key characteristics of electrodes (i.e. pore structure and electrode loading/thickness) affecting cell performance at low temperatures.To improve the low temperature performance of the Na2SO4-PAM electrolyte, several anti-icing additives (e.g. dimethyl sulfoxide/DMSO or ethylene glycol/EGly) have been investigated and shown promising improvement to the ionic conductivity of the electrolyte at low temperatures. Leveraging the polymer electrolyte with these additives, capacitive CV profiles were attained at -10 ˚C (Fig. 1a), much more pronounced than their binary baseline. The cell performance with the DMSO-containing ternary electrolyte was then evaluated using either CNT or AC electrodes at various carbon loadings (Fig. 1b). Although solid cells with AC electrodes demonstrated higher capacitance at ambient, those with CNT electrodes retained more capacitance at low temperature. This is likely due to better ion accessibility into CNT electrodes with relatively more open pores. Meanwhile, AC electrodes with lower carbon loading have higher capacitance retention at low temperature due to better electrode utilization in a thinner electrode. These observations will provide the guideline for designing the next generation of ECs that are suitable for low temperature applications.

Ternary Ionogel Electrolytes Enable Quasi‐Solid‐State Potassium Dual‐Ion Intercalation Batteries

A dual‐ion battery (DIB) is an emerging technology destined for use in stationary energy storage applications. Most DIB prototypes use expensive salt‐concentrated liquid electrolytes to ensure sufficient ion supply and an electrochemical stability window beyond 4.5 V, which is required for anion intercalation in graphite. Herein, the design of a compact quasi‐solid‐state potassium‐based DIB is introduced using ternary ionogel electrolytes (t‐IGEs) prepared from a potassium salt, an ionic liquid, and a poly(ionic liquid). Among a series of combinations, the t‐IGE with optimum mechanical property, thermal stability (>200 °C), and electrochemical performance consists of 30% salt, 28% ionic liquid, and 42% poly(ionic liquid). With ionic conductivity ranging from 0.1 to 1 mS cm−1 at 30–100°C and an electrochemical stability window within 0.5–5.0 V versus K+/K, the t‐IGE is suited for practical MoS2–graphite KDIBs. Infusing the ionogel in plain‐weave glass fiber fabrics (≈40 μm thick) further enables the design of more compact KDIBs in which a significant reduction (≈64%) in electrolyte thickness is achieved. The cells are able to deliver specific capacities varying from 80 to 25 mAh g−1 at 10 to 160 mA g−1, with CEs ranging from ≈90% to 100%.

Ionic liquid plasticizers comprising solvating cations for lithium metal polymer batteries

Ternary solid polymer electrolytes (TSPEs) with ionic liquids (ILs) including alkyl-based ammonium cations and low coordinating anions suffer from the lack of Li+ ion coordination by the ILs compared to the immobile polymer backbone, in terms of Li+ ion transport. Thus, solvating ionic liquids (SILs) with an oligo(ethylene oxide) side chain attached onto the cation were prepared to improve the interaction between Li+ and the IL and accelerate Li+ transport in TSPEs. A variety of methods, such as pulsed field gradient nuclear magnetic resonance spectroscopy, Li metal plating/stripping and measurements of Sand's times were used to show that Li+ ion transference numbers increase with the oligo(ethylene oxide) side chain length in SIL-based TSPEs, which results in faster Li+ ion transport and translates into much slower lithium depletion at a given current, thereby delaying the onset of fast dendrite growth of lithium metal.

Mutual Comparison Studies of Mono and Di Cations in Binary and Ternary Aqueous Electrolytes Solution at 298.15 K

Densities and viscosities of binary and ternary electrolytes solution have been determined experimentally at 298.15 K. The results obtained from density and viscosity measurement have been used to calculate apparent molar volume φv partial molar volume φov at infinite dilution, relative viscosities hrel, A and B coefficients, and free energies of activation of viscous flow of solvent Δ µ10# and solute Δ µ20. The results are discussed in terms of the dehydration effect of the weak ion-ion and strong ion-solvent interactions. The properties of these systems are discussed in terms of the charge, size, and hydrogen bonding effect.

Unveiling the diffusion-controlled operation mechanism of all-in-one type electrochromic supercapacitors: Overcoming slow dynamic response with ternary gel electrolytes

All-in-one electrochromic supercapacitors (ECSs) based on a single electrochromic (EC) gel layer are an attractive electronic component owing to their structural simplicity and capacitive and EC dual-function. Understanding the operating mechanism of ECSs is essential to maximize device performance. Particularly, the correlation between EC gel properties and ECS performance has not been properly established. In this study, the diffusion-controlled operating principle of the all-in-one ECSs is elucidated. The charging-discharging behaviors of ECSs based on conventional ion gels consisting of copolymer gelators and ionic liquids are incomplete due to the slow device dynamics arising from the delayed mass transport of redox-active materials through diffusive motion. Therefore, we propose the use of ternary gel electrolytes (TGEs) containing small organic molecules to reduce the overall viscosity and enlarge the free volume in the gel. A sufficient number of redox species can participate in galvanostatic charging-discharging reactions when the all-in-one ECSs are fabricated with highly conductive and elastic TGEs, resulting in a 3.3-times higher capacity (∼6.3 mC cm–2) than those based on typical ion gels (∼1.9 mC cm–2). Moreover, the TGE-based devices overcome the trade-off between transmittance contrast and response time, leading to superb performance. This study improves the overall performance and practical feasibility of all-in-one gel-based ECSs.

Alternative formalism for the evaluation of the activity coefficients on ternary electrolyte solutions from osmotic coefficient data

An alternative method is presented, which is independent of any physicochemical model of the electrolyte solution, for the evaluation of the mean ionic activity coefficient in molal scale, γ±i (i: 2,3), of the solutes of a ternary solution (1–2–3), starting from experimental data of the osmotic coefficient on composition ϕexp(m,xi). It is based on the dependence of ln γ±i on ϕ originally derived by H.A.C. McKay and confirmed by S.G. Canagaratna and M. Maheswaran as a particular solution of Gibbs-Duhem equation for multicomponent systems. Its application involves the integration of both ϕ and its derivative ∂ϕ/∂mi, so that it requires a very precise correlation of the dependence ϕexp(m,xi). Therefore, in order to achieve the required precision, the theoretical expression ϕ(m,xi) is developed as the sum of three contributions, (i) ϕDH: the limiting behaviour given by the Debye-Hückel equation for multicomponent systems, (ii) ΔϕDDH: the sum of the deviations to the Debye-Hückel behaviour of the corresponding binary solutions (1–2 and 1–3) and (iii) ΔϕM: a contribution of mixing effect. Finally, introducing the resulting ϕ(m,xi) into the Gibbs-Duhem equation and operating, the corresponding expression of ln γ±i (m,xi) is derived. The capacity of the ϕ(m,xi) equation to correlate the dependence ϕexp(m,xi), the methodology employed to obtain the parameters values, as well as the ln γ±i (m,xi) resulting dependence are illustrated through its application to the analysis of two ternary systems.

Measurement and modeling of mean activity coefficients in ternary electrolyte system (Nicl2/Triton X-100/H2O) at T=298.15 ± 0.1 K

In this work, the results relating to the thermodynamic properties for the ternary electrolyte system of (NiCl2 + Triton X-100 + water) using the potentiometric method were reported at T = 298.15 K. The electromotive force measurements were carried out on the galvanic cell without liquid junction of the type: Ni2+-ISE | NiCl2 (m), Triton X-100 (%wt.), H2O (100-%wt.) | AgCl|Ag over total ionic strengths from 0.0010 to 6.0000 mol.kg-1 for different percentage mass fraction of Triton X-100 (%wt. = 0.0, 1.0, 2.5, 5.0, 7.5 and 10.0). The mean activity coefficients of NiCl2 were determined by using potentiometric data. Then, the mean activity coefficients of NiCl2 were correlated with Pitzer ion interaction model and TCPC model. The Pitzer ion-interaction parameters (βo, β1 and C^∅) and the adjustable parameters (b and S) of TCPC model were determined by correlating of data for the series under investigated system. The Pitzer ion interaction parameters were used to calculating of thermodynamic properties such as the osmotic coefficients and the excess Gibbs energy of solution. The result showed that the Pitzer ion interaction model could be used to investigation of the system, successfully.

Ionic Liquids: Design Parameters for Ionic Liquid–Molecular Solvent Blend Electrolytes to Enable Stable Li Metal Cycling Within Li–O2 Batteries (Adv. Funct. Mater. 27/2021)

In article number 2010627, Alex R. Neale, Laurence J. Hardwick, and co-workers present the stability enhancements at Li-metal anodes for Li-O2 cells using concentrated ternary electrolytes based on DMSO and an ionic liquid. Optimizing the critical DMSO–Li+ solvation interactions protects the solvent at the Li metal interface, inhibiting corrosion reactions and dendritic deposition that occur in the presence of free DMSO, and improves the overall performance within Li-O2 cells.

Multi-ionic electrolytes and E.coli removal from wastewater using chitosan-based in-situ mediated thin film composite nanofiltration membrane

This work presents the experimental investigation of flat sheet composite nanofiltration membrane synthesized with chitosan nanoparticles through interfacial polymerization of piperazine with trimesoyl chloride on polyethersulfone/sulfonated polysulfone substrates. The synthesized membrane was tested in wastewater treatment containing inorganic salts and E.Coli. Single binary electrolyte solution of KCl, MgCl2, MgSO4, and Na2SO4, ternary electrolyte solution, containing a combination of MgCl2 and MgSO4, KCl and MgCl2 and quaternary electrolyte solution of KCl, MgCl2, and MgSO4 as feed were treated in crossflow membrane cell for the water flux and species rejection in the permeate under operating pressure up to 0.5 MPa. The rejection of Na1+, K1+, Mg2+, Cl1−, and SO42− was observed to be 81, 28, 87, 96, and 98%, respectively with an average water flux up to 214 ± 10 L m⁻2.hr⁻1 in the permeate for the binary electrolyte solution. Similarly, the rejection for K1+, Mg2+, Cl1− and SO42− was noted to be 33, 94, 97, and 99%, respectively, for ternary electrolyte solution with an average water flux up to 211 ± 10 L m−2.hr−1. The quaternary ion system in the feed resulted in an average water flux up to 198 ± 12 L m⁻2.hr⁻1 with the rejection of K+, Mg+2, Cl− and SO4−2 as 35, 87, 96, and 99%, respectively. The model feed solution of E. coli after passing through the membrane achieved an E. coli rejection (99%) with water flux up to 220 L m−2.hr−1.

Effect of current density, concentration of ternary electrolyte and type of cations on the monovalent ion selectivity of surface-sulfonated graft anion-exchange membranes: modelling and experiment

The dependence of monovalent-ion selectivity of surface-sulfonated anion exchange membranes (s-AEMs) on the electrodialysis (ED) desalination current density, the concentration of equimolar ternary electrolyte (XCl + X2SO4) in the total concentration range 0.04–0.2 M, and the type of cations (X = H, Cs, Na) has been studied. The membrane current-voltage characteristics and values of the diffusion permeability coefficients in electrolyte solutions and their mixtures were measured. It was shown that Cl/SO4-selectivity coefficients (PCl|SO4) increase along with current density, reaching maximum values at the limiting current density (Ilim). The PCl|SO4 maximum value of 5.5 was achieved for the s-AEM-18 membrane in the ED-desalination of equimolar ternary electrolytes NaCl/Na2SO4, and CsCl/Cs2SO4 (total salt concentration 0.04 M) at 1.4 and 2.4 mA cm−2 current densities, respectively. At the overlimiting currents, the splitting of water and the decrease of Cl/SO4-selectivity were observed. The obtained experimental results are interpreted using simplified mass transfer and numerical simulations in the framework of Nernst-Planck-Poisson equations implemented in the COMSOL® Multiphysics software. The model represents the modified membrane as an asymmetric bipolar membrane with two diffusion boundary layers (DBL) in electrolyte solutions on both sides of the membrane interface. The model includes the water splitting at the bipolar boundary and the chemical equilibrium between sulfate and hydrogen sulfate ions. The numerical simulations qualitatively predict the behaviour of s-AEMs membranes when the abovementioned conditions change.

A new NRTL-based local composition model for thermodynamic modeling of electrolyte solutions

A new local composition model for the expression of excess Gibbs energies and activity coefficients in binary and multicomponent electrolyte solutions is presented in this work. The model is based on the nonrandom two-liquid (NRTL) theory and is developed assuming the random contribution of ions and molecules around central species at reference state. The new model provides a completely new formulation for the expression of short-range interactions in electrolyte solutions. The accuracy of developed equations is examined using the available experimental data for several aqueous electrolyte systems at vast ranges of concentration and temperature. The results are compared with those obtained from eNRTL model. Two binary interaction parameters of the model are adjusted for numerous binary salt-water systems through the accurate correlation of the mean ionic activity coefficient data. Adjusted parameters are then successfully used for the prediction of osmotic coefficients in binary systems. When compared to the eNRTL model, the new model is more accurate. That superiority is very significant for the systems which are highly non-ideal. To examine the adequacy of the model for multicomponent systems, available experimental solubility and osmotic coefficient data of different ternary aqueous electrolyte systems are compared to the values predicted by the model. Using only the previously adjusted binary interaction parameters, the predicted values are in very good agreement with the experimental data.

The Hydrotropic Effect of Ionic Liquids in Water‐in‐Salt Electrolytes**

AbstractWater‐in‐salt electrolytes have successfully expanded the electrochemical stability window of aqueous electrolytes beyond 2 V. Further improvements in stability can be achieved by partially substituting water with either classical organic solvents or ionic liquids. Here, we study ternary electrolytes composed of LiTFSI, water, and imidazolium ionic liquids. We find that the LiTFSI solubility strongly increases from 21 mol kg−1 in water to up to 60 mol kg−1 in the presence of ionic liquid. The solution structure is investigated with Raman and NMR spectroscopy and the enhanced LiTFSI solubility is found to originate from a hydrotropic effect of the ionic liquids. The increased reductive stability of the ternary electrolytes enables stable cycling of an aqueous lithium‐ion battery with an energy density of 150 Wh kg−1 on the active material level based on commercially relevant Li4Ti5O12 and LiNi0.8Mn0.1Co0.1O2 electrode materials.

The Hydrotropic Effect of Ionic Liquids in Water-in-Salt Electrolytes*.

Water-in-salt electrolytes have successfully expanded the electrochemical stability window of aqueous electrolytes beyond 2 V. Further improvements in stability can be achieved by partially substituting water with either classical organic solvents or ionic liquids. Here, we study ternary electrolytes composed of LiTFSI, water, and imidazolium ionic liquids. We find that the LiTFSI solubility strongly increases from 21 mol kg-1 in water to up to 60 mol kg-1 in the presence of ionic liquid. The solution structure is investigated with Raman and NMR spectroscopy and the enhanced LiTFSI solubility is found to originate from a hydrotropic effect of the ionic liquids. The increased reductive stability of the ternary electrolytes enables stable cycling of an aqueous lithium-ion battery with an energy density of 150 Wh kg-1 on the active material level based on commercially relevant Li4 Ti5 O12 and LiNi0.8 Mn0.1 Co0.1 O2 electrode materials.

Efficient Electroreduction of CO2 to CO on Porous ZnO Nanosheets with Hydroxyl Groups in Ionic Liquid‐based Electrolytes

AbstractElectrochemical reduction of CO2 is a very promising route to realize carbon cycle and alleviate energy shortage. Herein, the porous zinc oxide nanosheets with hydroxyl groups on carbon paper substrates (ZnO(OH)/CP‐x,×represents the deposition time) were proved to be excellent catalysts for CO2 electroreduction to CO. As far as we know, the hydroxyl groups were first introduced into ZnO catalysts for this reaction, which can enhance the surface areas and improve the capacity of binding CO2 by the formation of hydrogen bond. Especially, the total current density could reach 44.3 mA cm−2 with 97.8 % Faradaic efficiency (FE) of CO over ZnO(OH)/CP‐600 catalysts with moderate hydroxyl groups in 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim]PF6, 30 wt%)/acetonitrile/H2O (5 wt%) ternary electrolytes at −2.0 V versus Ag/Ag+, although the self‐reduction of the catalysts could be occurred simultaneously during electrolysis. Besides, the composition of the electrolytes also can significantly modulate the catalytic activity and selectivity of CO. The outstanding performance of ZnO(OH)/CP‐600 catalyst resulted mainly from the introduction of hydroxyl groups, high surface area, good contact with the substrate, and synergy effect between the catalyst and the electrolyte.

TYPE OF WEAR OF ALUMINIUM OXIDE LAYERS DEPENDING ON MANUFACTURING PARAMETERS

The article presents the type of wear of Al2O3 layers produced on the aluminium alloy EN AW-5251 depending on the production parameters. Oxide layers were produced by using DC anodizing in a ternary electrolyte at variable current density and electrolyte temperature. The layer scratch tests were carried out using a Micron- Gamma microhardness tester. The scratches of oxide layers were tested for the geometric structure of the surface using a Form TalySurf 2 50i contact profilograph. Contact thickness measurements were also made using a Dualscope MP40 device based on the eddy-current method. Using a scanning microscope (SEM), photos of the sample surfaces were taken to show and compare the surface morphology of the anodized layers in various parameters. Based on the research, it can be concluded that changes in the conditions of the production process of Al2O3 layers (electrolyte temperature and current density) have an impact on the type of tribological wear and changes in layer thickness. The largest thickness of the oxide layer (19.44 μm) was measured for Sample B produced at a current density of 3A/dm2 at an electrolyte temperature of 283 K, which was also characterized by the lowest value of the ratio of parameters f1 to f2 (0.584). The smallest thickness (5.32 μm) was measured for the Sample C anodized at 1 A/dm2 at 303 K, this sample had the largest ratio f1 to f2 (1.068) for the produced Al2O3 layers. Thanks to the parameters f1 and f2 and the calculation of their ratio, the wear process for Sample B was determined as scratching and microcutting, while for Sample C as grooving.

Composite Lithium Protective Layer Formed In Situ for Stable Lithium Metal Batteries

Lithium metal is considered as the ideal anode for next-generation rechargeable batteries due to its highest theoretical specific capacity and lowest electrochemical potential. However, lithium dendrite growth during lithium deposition could lead to a short circuit and even cause severe safety issues. Here, we use solid-state electrolyte Li3InCl6 as an additive in nonaqueous electrolytes because of its high ionic conductivity (10-3 to 10-4 S cm-1) and good electrochemical stability. It is found that Li3InCl6 can in situ react with metallic lithium to form a ternary composite solid electrolyte interphase (SEI) consisting of a Li-In alloy, LiCl, and codeposited Li3InCl6. The composite SEI can effectively suppress Li dendrite growth and thereby maintain stable long-term cycling performance in lithium metal batteries. The protected lithium electrode exhibits stable cycling performance in a symmetric Li|Li battery for nearly 1000 h at a current density of 1 mA cm-2. Besides, the full battery with a LiFePO4 cathode and a metallic lithium anode delivers a stable capacity of 140.6 mA h g-1 for 500 cycles with a capacity retention of 95%. The Li|S battery with Li3InCl6-added LiTFSI in 1,3-dioxolane/1,2-dimethoxyethane electrolyte also shows significant improvement in capacity retention at 0.5 C. This work demonstrates an effective approach to design dendrite-free metal anodes.

Systematic Investigation of Electrochemical Performances for Lithium-Ion Batteries with Si/Graphite Anodes: Effect of Electrolytes Based on Fluoroethylene Carbonate and Linear Carbonates

Fluoroethylene carbonate (FEC) is known as an effective additive to improve the performance of silicon-based anodes, but the improvement is rather limited in full-cell configuration. In this work, we utilize FEC as a main solvent to establish binary or ternary electrolytes and systematically investigate their electrochemical performance in LiNi0.5Co0.2Mn0.3O2∥Si/graphite full-cells. Compared with a commercial electrolyte, the cycle stability and reversibility of the full-cells are remarkably improved during the prolonged cycle test (500 cycles) at ambient temperature. The cells with FEC-based electrolytes demonstrate higher specific capacities at 55 °C for the 200 cycles galvanostatic cycle test, and it shows good rate capacity retention under high current (up to 5 C) at ambient temperature. In particular, the low-temperature performances of the full-cells are prominent; among the tested samples, the FEC/DMC (5:5) electrolyte delivers an outstanding capacity as high as 92.3 mA h g–1 at −40 °C. These results would endow such FEC-based electrolytes with great potential for practical applications.

Dimethyl sulfoxide additive to Na2SO4-based polymer electrolytes for low temperature capacitive devices

Dimethyl sulfoxide (DMSO) was added to an aqueous-based Na2SO4-polyacrylamide (PAM) electrolyte to improve its low temperature performance. The addition of DMSO significantly enhanced the ionic conductivity of Na2SO4-PAM binary electrolyte at sub-zero temperatures, while virtually maintained their excellent properties at and above ambient temperature. The improvement in low temperatures was correlated to the lower melting point and smaller crystal hydrates at freezing point. Solid capacitor cells using carbon nanotube electrodes with the ternary Na2SO4-PAM-DMSO electrolytes were assembled and compared against the binary Na2SO4-PAM baseline. Under ambient conditions, both cells showed similarly wide 1.8 V window and excellent rate capability. While the cells with binary electrolytes showed pure resistive behaviour at -20 °C, those with ternary electrolytes showed significant improvement in their capacitive voltammogram profile and impedance spectra. The results showed that DMSO can be effective in widening the operating temperature of neutral pH polymer electrolytes and their enabled solid capacitive devices.