Acetonitrile-based Electrolyte Research Articles

Acetonitrile-Based Local High-Concentration Electrolytes for Advanced Lithium Metal Batteries.

Acetonitrile (AN) is a compelling electrolyte solvent for high-voltage and fast-charging batteries, but its reductive instability makes it incompatible with lithium metal anodes (LMAs). Herein, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is used as the diluent to build an AN-based local high-concentration electrolyte (LHCE) to realize dense, dendrite-free, and stable LMAs. Such LHCE exhibits an exceptional electrochemical stability window close to 6V (vs Li+/Li), excellent wettability, and promising flame retardancy. Compared to a baseline carbonate-based electrolyte, its electrochemical performance is prominent: the overpotential of lithium nucleation is minimal (only 24mV), the average half-cell coulombic efficiency (CE) reaches 99.5% at 0.5mAcm-2, and its practicality in full cells with LiFePO4 (LFP) and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes is also demonstrated. Compounding factors are identified to decipher the superiority of the AN-based LHCE. From the respect of solvation structures, both the elimination of free AN molecule and the diluent separation would contribute to prevention of anodic AN decomposition. Based on cryogenic electron microscopy (Cryo-EM) characterization and theoretical simulations results, the produced solid-electrolyte interphase (SEI) layer is uniform and compact. Thus, this work demonstrates a successful application of AN-based electrolytes in LMAs-traditionally deemed impractical-via the combined regulation of solvation and SEI structures.

Phosphonate-based supercapacitor electrolyte integrating the advantages of flame retardancy, extreme temperature adaptability, and anti-supergravity

Traditional acetonitrile-based organic electrolytes continue to dominate in carbon-based supercapacitors due to their high performance-to-price ratio. However, its flammability, low extreme temperature applicability, and unknown anti-supergravity limit its application in some special scenarios (e.g., space exploration). For the first time, an electrolyte system based on potassium hexafluorophosphate (KPF6) and diethyl ethylphosphonate (DEEP) as the electrolyte salt and solvent, respectively, was proposed. The KPF6/DEEP system combines excellent flame retardancy, high capacitance performance at high (60 °C) and low (-70 °C) temperatures, anti-supergravity (60 G), and an operating voltage of up to 3.0 V, resulting in a stable and high power energy output of up to 16 Wh kg−1 for carbon-based supercapacitors at −60 °C. These benefits are primarily attributed to the distinct physical properties of DEEP (e.g., flame retardancy, low freezing point, high boiling point, and high compatibility with KPF6). Such outstanding overall performance, which incorporates excellent flame retardancy, extreme temperature adaptability, anti-supergravity, and cycle stability (capacity retention > 95 % after 14,000 cycles), outperforms the traditional acetonitrile-based system, opening up a new option for power devices for some applications with extreme environmental demands.

Mechanistic Basis of Conductivity in Carbon Dioxide-Expanded Electrolytes: A Joint Experimental-Theoretical Study.

Electrolyte conductivity contributes to the efficiency of devices for electrochemical conversion of carbon dioxide (CO2) into useful chemicals, but the effect of the dissolution of CO2 gas on conductivity has received little attention. Here, we report a joint experimental-theoretical study of the properties of acetonitrile-based CO2-expanded electrolytes (CXEs) that contain high concentrations of CO2 (up to 12 M), achieved by CO2 pressurization. Cyclic voltammetry data and paired simulations show that high concentrations of dissolved CO2 do not impede the kinetics of outer-sphere electron transfer but decrease the solution conductivity at higher pressures. In contrast with conventional behaviors, Jones reactor-based measurements of conductivity show a nonmonotonic dependence on CO2 pressure: a plateau region of constant conductivity up to ca. 4 M CO2 and a region showing reduced conductivity at higher [CO2]. Molecular dynamics simulations reveal that while the intrinsic ionic strength decreases as [CO2] increases, there is a concomitant increase in ionic mobility upon CO2 addition that contributes to stable solution conductivities up to 4 M CO2. Taken together, these results shed light on the mechanisms underpinning electrolyte conductivity in the presence of CO2 and reveal that the dissolution of CO2, although nonpolar by nature, can be leveraged to improve mass transport rates, a result of fundamental and practical significance that could impact the design of next-generation systems for CO2 conversion. Additionally, these results show that conditions in which ample CO2 is available at the electrode surface are achievable without sacrificing the conductivity needed to reach high electrocatalytic currents.

Regulating the solvation structure of an acetonitrile-based electrolyte for Li/NMC811 batteries cycled at low temperature

An acetonitrile-based localized high concentration electrolyte has been developed for low temperature lithium metal batteries. The corresponding Li/NMC811 cell delivers a high capacity of 113 mA h g−1 at −40 °C with 85.5% capacity retention.

Whole Landscape of the Origin and Evolution of Gassing in Supercapacitors at a High Voltage.

Although supercapacitors with acetonitrile-based electrolytes (AN-based SCs) have realized high-voltage (3.0 V) applications by manufacturers, gas generation at high voltages is a critical issue. Also, the exact origins and evolution mechanisms of gas generation during SC aging at 3.0 V still lack a whole landscape. In this work, floating tests under realistic working conditions are conducted by 22450-type cylindrical cells with an AN-based commercial electrolyte. Comprehensive insights into the origins and evolution mechanisms of gas species at 2.7 and 3.0 V are acquired, which involves multiple side reactions related to the electrode, current collector, and electrolyte. Both experimental evidence and density functional theory calculations demonstrate that the primary reasons for gas generation are residual water and oxygen-containing functional groups, especially hydroxyl and carboxyl. More importantly, additional types of gas (such as CO2, NH3, and alkenes) can only be detected at a higher voltage of 3.0 V rather than 2.7 V after failure, suggesting that these gas species can be regarded as the failure signatures at 3.0 V. This breakthrough analysis will provide fundamental guidance for failure evaluation and designing AN-based SCs with extended lifetime at 3.0 V.

Scalable Electrodeposition of Liquid Metal from an Acetonitrile-Based Electrolyte for Highly Integrated Stretchable Electronics.

The advancement of highly integrated stretchable electronics requires the development of scalable sub-micrometer conductor patterning. Eutectic gallium indium (EGaIn) is an attractive conductor for stretchable electronics, as its liquid metallic character grants it high electrical conductivity upon deformation. However, its high surface tension makes its patterning with sub-micrometer resolution challenging. In this work, this limitation is overcome by way ofthe electrodeposition of EGaIn. A non-aqueous acetonitrile-based electrolyte that exhibits high electrochemical stability and chemical orthogonality is used. The electrodeposited material leads to low-resistance lines that remain stable upon (repeated) stretching to a 100% strain. Because electrodeposition benefits from the resolution of mature nanofabrication methods used to pattern the base metal, the proposed "bottom-up" approach achieves a record-high density integration of EGaIn regular lines of 300nm half-pitch on an elastomer substrate by plating on a gold seed layer prepatterned by nanoimprinting. Moreover, vertical integration is enabled by filling high-aspect-ratio vias. This capability is conceptualized by the fabrication of an omnidirectionally stretchable 3D electronic circuit, and demonstrates a soft-electronic analog of the stablished damascene process used to fabricate microchip interconnects. Overall, this work proposes a simple route to address the challenge of metallization in highly integrated (3D) stretchable electronics.

A Bifunctional Ionic Liquid for Capture and Electrochemical Conversion of CO2 to CO over Silver.

Electrochemical conversion of CO2 requires selective catalysts and high solubility of CO2 in the electrolyte to reduce the energy requirement and increase the current efficiency. In this study, the CO2 reduction reaction (CO2RR) over Ag electrodes in acetonitrile-based electrolytes containing 0.1 M [EMIM][2-CNpyr] (1-ethyl-3-methylimidazolium 2-cyanopyrolide), a reactive ionic liquid (IL), is shown to selectively (>94%) convert CO2 to CO with a stable current density (6 mA·cm-2) for at least 12 h. The linear sweep voltammetry experiments show the onset potential of CO2 reduction in acetonitrile shifts positively by 240 mV when [EMIM][2-CNpyr] is added. This is attributed to the pre-activation of CO2 through the carboxylate formation via the carbene intermediate of the [EMIM]+ cation and the carbamate formation via binding to the nucleophilic [2-CNpyr]- anion. The analysis of the electrode-electrolyte interface by surface-enhanced Raman spectroscopy (SERS) confirms the catalytic role of the functionalized IL where the accumulation of the IL-CO2 adduct between -1.7 and -2.3 V vs Ag/Ag+ and the simultaneous CO formation are captured. This study reveals the electrode surface species and the role of the functionalized ions in lowering the energy requirement of CO2RR for the design of multifunctional electrolytes for the integrated capture and conversion.

Electrochemical characterization of Ti3C2Tx MXene prepared via a molten salt etching route in an acetonitrile-based electrolyte

Two-dimensional metal carbide and nitride materials (MXenes) with controlled Cl- and O-surface terminations (MS-Ti3C2Tx) were prepared by a molten salt etching route and their electrochemical properties were investigated in nitrile-based electrolytes. The results show that the power performance of MS-Ti3C2Tx was greatly improved in acetonitrile (ACN)-based non-aqueous organic electrolytes, which are conventional electrolytes for electrochemical capacitors. The addition of a lithium salt to produce 2 M LiTFSI in ACN results in an increase in the specific capacitance. Moreover, replacing LiTFSI by LiFSI drastically improves the power performance of MXenes at a high scan rate (95 mAh g−1 at 900C). These results highlight the importance of properly matching the electrolyte composition to the electrode material and shed light on MXenes as high-rate electrode materials for energy storage applications.

Liquid crystals purity assay using nonaqueous capillary electrokinetic chromatography.

A method for purity control of newly synthesized lactic acid-based liquid crystals has been developed. The electrokinetic chromatography proved to be suitable for the separation of these electroneutral substances from their impurities. The separations were performed in an acidic acetonitrile-based background electrolyte (BGE) with a pseudostationary phase formed by a cationic surfactant. During the optimization step, appropriate concentrations of cetyltrimethylammonium bromide, acetic acid, and water were seeked. In the optimized method, separations were carried out in acetonitrile with 1-mol/L acetic acid, 80-mmol/L cetyltrimethylammonium bromide, and 6% (v/v) water. Interesting positive effects of a small water content in the BGE on electroosmotic flow and resolution of liquid crystal substances from their impurities were observed and discussed. Samples of five liquid crystal substances, both pure and containing impurities from synthesis, were analyzed. The identification of analytes was based on a comparison of relative migration times related to the migration time of mesityl oxide. For all five samples, impurities were separated from the liquid crystals and the method thus showed its viability. To the best of our knowledge, this method is used for the first time for the purity control of newly synthesized liquid crystals. This method can be used to confirm or complement the results obtained by commonly used high-performance liquid chromatography and supercritical fluid chromatography methods. Furthermore, the electrokinetic chromatography method requires very small amounts of sample, solvents, and buffer constituents. Overall, its operational costs are significantly lower.

MXene-based Zn-ion hybrid supercapacitors: Effects of anion carriers and MXene surface coatings on the capacities and life span

Energy storage devices such as rechargeable batteries and supercapacitors are of great importance for establishing clean energy sources. Accordingly, the production of these devices needs to rely on sustainable and environmentally friendly materials. This report provides an insight on the use of two-dimensional transition metal carbides (MXene) based electrodes, here shown for Mo1.33CTz-Ti3C2Tz mixed MXene, in Zn-ion hybrid supercapacitors (ZHSC) using aqueous and nonaqueous (acetonitrile-based) electrolytes. The effect of anion carriers on the accessible capacity, rate capability, and life span of the MXene//Zn hybrid supercapacitor is explored in-depth. Halide carriers such as chloride (Cl−) and iodide (I−) feature a superior performance, however, a fast passivation is observed in Cl− based electrolytes and a narrow potential window is achieved in I− based electrolytes. Importantly, a few micron layer of Ti3C2Tz MXene coated on the surface of the Zn anode is found to inhibit the side reactions and passivation observed in ZnCl2 solutions, which enables the use of such low-cost Zn salt in MXene//Ti3C2Tz-coated-Zn cells. The cells can be reversibly cycled over 10,000 cycles, delivering a capacity up to 200 mAh g−1 at low rate (0.5 mV s−1) and a capacity retention of about 36% at high rate (100 mV s−1). Furthermore, the Ti3C2Tz surface coating layer enhanced the coulombic efficiency in Zn(CF3SO3)2 electrolyte without affecting the accessible capacity or the rate capability. This work sheds light on the use of MXenes in sustainable low-cost ZHSC with high energy density and power density as a positive electrode material as well as a surface coating material for the Zn negative electrode.

Electrical Transport, Structural, Optical and Thermal Properties of [(1-x)Succinonitrile: xPEO]-LiTFSI-Co(bpy)3(TFSI)2-Co(bpy)3(TFSI)3 Solid Redox Mediators.

The solar cell has been considered one of the safest modes for electricity generation. In a dye-sensitized solar cell, a commonly used iodide/triiodide redox mediator inhibits back-electron transfer reactions, regenerates dyes, and reduces triiodide into iodide. The use of iodide/triiodide redox, however, imposes several problems and hence needs to be replaced by alternative redox. This paper reports the first Co2+/Co3+ solid redox mediators, prepared using [(1−x)succinonitrile: xPEO] as a matrix and LiTFSI, Co(bpy)3(TFSI)2, and Co(bpy)3(TFSI)3 as sources of ions. The electrolytes are referred to as SN_E (x = 0), Blend 1_E (x = 0.5 with the ethereal oxygen of the PEO-to-lithium ion molar ratio (EO/Li+) of 113), Blend 2_E (x = 0.5; EO/Li+ = 226), and PEO_E (x = 1; EO/Li+ = 226), which achieved electrical conductivity of 2.1 × 10−3, 4.3 × 10−4, 7.2 × 10−4, and 9.7 × 10−7 S cm−1, respectively at 25 °C. Only the blend-based polymer electrolytes exhibited the Vogel-Tamman-Fulcher-type behavior (vitreous nature) with a required low pseudo-activation energy (0.05 eV), thermal stability up to 125 °C, and transparency in UV-A, visible, and near-infrared regions. FT-IR spectroscopy demonstrated the interaction between salt and matrix in the following order: SN_E < Blend 2_E < Blend 1_E << PEO_E. The results were compared with those of acetonitrile-based liquid electrolyte, ACN_E.

Dead volume-free flow splitting in capillary electrophoresis.

In recent years, several dual detection concepts (DDCs) for CE were developed, which consisted of at least one nondestructive detector. For these DDCs, a linear detector arrangement could be used, which is not possible when both detectors are destructive. To overcome this problem, we developed a concept for the splitting of the CE stream utilizing commercially available flow splitters (FSs) that allow the parallel positioning of two destructive detectors. In this proof-of-concept study, T- and Y-shaped FSs were characterized regarding their suitability for DDCs. To keep it simple, a UV detector (UV) and a C4 D were used for the characterization. The model system consisted of an acetonitrile-based background electrolyte and the two model substances, (ferrocenylmethyl)trimethylammonium iodide and caffeine. CE hyphenated to a UV detector (CE-UV) measurements revealed that the split ratio was about 50% for both FSs. CE-C4 D was used to evaluate the peak shape in front of and behind the FSs. These measurements showed that there was no significant peak broadening introduced by the FSs. Additionally, there were no changes in the LODs in front of and behind the FSs. Furthermore, the flexibility of the new FS approach allowed the usage of capillaries with different ids (25-75µm) for injection and detection.

Investigation of Electrochemical Performance and Gas Swelling Behavior on Li4Ti5O12/Activated Carbon Lithium-Ion Capacitor with Acetonitrile-Based and Ester-Based Electrolytes

Lithium-ion capacitors (LICs) have gained significant attention due to the combination on the advantages of electric double-layer capacitors (EDLCs) and lithium-ion batteries (LIBs). Herein, the LIC pouch cell was fabricated by an activated carbon (AC) cathode and a Li4Ti5O12 (LTO) anode. Two organic electrolytes (1 mol L−1 LiBF4/acetonitrile (AN) and 1 mol L−1 LiPF6/ ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + dimethyl carbonate (DMC)) were chosen and the gas swelling behavior was studied. Compared with the ester-based LIC, the AN-based LIC displays higher energy density of 13.31 Wh kg−1 at 11.4 W kg−1 and even provides a value of 9.1 Wh kg−1 at 1075 W kg−1. Because of the lower DC Resistance of 0.761 mΩ, the maximum power density of the AN-based LIC reaches 12.5 kW kg−1. The AN-based LIC delivers good stability with an energy retention of 88.3% after 900 cycles. It is discovered that the swelling behavior of AN-based LICs is more serious and the major component is H2. The difference of swelling behavior among the LICs, lithium nickel cobalt manganese oxide (NCM)/LTO LIB and AC/AC EDLC is proposed to be caused by the AC electrode and the interfacial reaction of LTO.

Capacitive Charge Storage at the Glassy Carbon Electrode: Comparison Between Aqueous and Non-Aqueous Electrolytes

Herein the charge storage capabilities of a planar non-porous glassy carbon electrode (GCE) in electrolytes of aqueous 0.5 M Na2SO4 and 1 M tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile are compared using a combination of cyclic voltammetry (CV), step potential electrochemical spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS). In all techniques the resultant capacitance was substantially higher for the GCE in 1 M TEABF4 compared to 0.5 M Na2SO4, with the differences due to solvation of the adsorbing electrolyte ions. Adsorbing Na+ cations in the aqueous system have a substantial solvation sheath that increases the resistance associated with capacitive charge storage, decreases the capacitance, as well as inhibits the packing of similar electrolyte ions in the vicinity of the GCE. Conversely, the adsorbing BF4− ions in the acetonitrile-based electrolyte exhibit a low resistance to charge storage, a greatly enhanced capacitance, as well as exhibit an improved ability to pack at the electrode-electrolyte interface. The impact of this behaviour on electrode performance has also been discussed.

Electroactivity of PIPO nitroxide radical polymer films

Nitroxide radical polymers (NRPs) are widely used as electroactive materials in a range of electrochemical applications, however, their preparation can be complex. Polyamine Immobilised Piperidinyl Oxyl (PIPO) is a commercially available, well-defined, NRP whose electrochemical properties have not been explored to date. Cyclic voltammetric (CV) studies demonstrate the electroactivity of PIPO in a range of organic electrolytes, displaying quasi -reversible redox waves, characteristic of a nitroxide radical / oxoammonium couple, with midpoint potentials in the range of 0.2 to 0.3 V vs. Fc + / Fc. When immobilised at a graphite electrode surface, PIPO maintains its electroactivity, forming stable, swellable films in acetonitrile-based electrolyte. Voltammetric and potentiometric analyses indicate that films can undergo repeated charge / discharge cycling, possibly facilitated by a diffusional controlled ‘electron hopping’ process. Furthermore, CV studies indicate that PIPO is an effective surface confined electrocatalyst for oxidation reactions of relevance to organic electrosynthesis and to lithium-air battery development. Such insights establish the basis for further investigations of PIPO as an accessible, cost-effective, and adaptable electroactive material for electrocatalytic and energy storage applications.

Characterization of linearly coupled capillaries with various inner diameters in the context of capillary electrophoresis

As a result of continuous instrumental progress, capillary electrophoresis has become an established separation technique. However, the choice of the suitable capillary inner diameter is sometimes difficult due to different instrumental requirements concerning injection, separation, or detection. To overcome this problem, we assembled two capillaries with different inner diameters, meaning that the inner diameter of the capillary at the injection side was different from that at the detection side. Since this was a rather uncommon approach, we focused on the associated effects in this proof-of-concept study. For the experiments, a non-aqueous model system was used, consisting of an acetonitrile-based background electrolyte and the two ferrocene derivates, ferrocenemethanol and decamethylferrocene. Using capillary flow injection analysis hyphenated to capacitively coupled contactless conductivity detection, it could be shown that fragmented capillaries of the same inner diameter had slightly lower volume flow rates than non-fragmented capillaries. With non-aqueous capillary electrophoresis hyphenated to UV detection, it was found that the coupling of capillaries with different inner diameter had a much stronger effect on the capillary electrophoresis flow than combinations with the same inner diameter. Additionally, if the inner diameter of the second capillary was larger than the inner diameter of the first capillary, a higher theoretical plate number and an increased sensitivity were found. Furthermore, it was found that there was no significant peak tailing introduced by the coupling.Graphic abstract

Quantifying ion desolvation effects on capacitances of nanoporous electrodes with liquid electrolytes

Understanding ion desolvation effect in microporous electrodes is helpful towards high-efficient energy storage. Herein, we evaluate the contribution of ion desolvation to the electrochemical performance of microporous electrodes with a proposed multiscale approach. By combining the molecular density functional theory (DFT) with the simple DFT, we determine the ion solvation diameters in confined liquid acetonitrile, and then predict the capacitances of microporous electrodes involving acetonitrile-based electrolytes through a solvation-diameter-dependent coarse-grained model. We find that the ion solvation diameter displays an oscillatory decline as decreasing the pore size of nanoslit. Integrating this decline relation with the pore size distributions of microporous electrodes we show that the capacitances of practical electrodes can be quantitatively predicted in comparison with experimental measurements. This work not only provides a promising multiscale approach for investigating the properties of confined electrolytes, but also casts insights for the design and preparation of high-performance supercapacitors.

Low-temperature energy storage performance of NiSalen type polymer and it's composite with SWCNT

Batteries and supercapacitors dramatically lose both energy and power at low temperatures. One of the possible routes to achieve reasonable low temperature performance is to use “soft” organic energy storage materials. Herein, composite material based on NiSalen-type polymer and single wall carbon nanotubes poly[Ni(CH3Salen)]/SWCNT was studied as the cathode material for low temperature batteries and supercapacitors with acetonitrile-based electrolyte. It was demonstrated that the composite performance is stable at temperatures below 0 °C, and the cell is retaining 80% of initial capacity at temperatures as low as −40 °C. The areal capacitance of the electrode, made from poly[Ni(CH3Salen)]/SWCNT composite, reaches 72 mF cm−2.

Two-Plateau Li-Se Chemistry for High Volumetric Capacity Se Cathodes.

For Li-Se batteries, ether- and carbonate-based electrolytes are commonly used. However, because of the "shuttle effect" of the highly dissoluble long-chain lithium polyselenides (LPSes, Li2 Sen , 4≤n≤8) in the ether electrolytes and the sluggish one-step solid-solid conversion between Se and Li2 Se in the carbonate electrolytes, a large amount of porous carbon (>40 wt % in the electrode) is always needed for the Se cathodes, which seriously counteracts the advantage of Se electrodes in terms of volumetric capacity. Herein an acetonitrile-based electrolyte is introduced for the Li-Se system, and a two-plateau conversion mechanism is proposed. This new Li-Se chemistry not only avoids the shuttle effect but also facilitates the conversion between Se and Li2 Se, enabling an efficient Se cathode with high Se utilization (97 %) and enhanced Coulombic efficiency. Moreover, with such a designed electrolyte, a highly compact Se electrode (2.35 gSe cm-3 ) with a record-breaking Se content (80 wt %) and high Se loading (8 mg cm-2 ) is demonstrated to have a superhigh volumetric energy density of up to 2502 Wh L-1 , surpassing that of LiCoO2 .

Fast anion intercalation into graphite cathode enabling high-rate rechargeable zinc batteries

Cheap, high-rate and long-life batteries are urgently needed for grid-scale storage of renewable energy. Rechargeable zinc (Zn) batteries are potential candidates due to the high volumetric energy density and low cost of Zn anode. However, conventional Zn batteries employing metal oxide cathodes usually suffer from poor rate capabilities caused by the high migration barrier of Zn2+ in the metal oxide host structure. Here, we circumvent this dilemma by integrating Zn electrochemistry with bis(trifluoromethanesulfonyl) imide (TFSI−) anion (de)intercalation into graphite cathode based on a Zn(TFSI)2/acetonitrile electrolyte. Owing to the fast intercalation of TFSI− along with the efficient Zn/Zn2+ redox kinetics, our Zn/graphite batteries enable an ultrafast charging rate up to 200C (to be fully charged in 18 s) and deliver a high power density of 16.3 kW kg−1, which is comparable to those of supercapacitors. Besides, the rational utilization of the acetonitrile-based electrolyte further endows the resultant battery with dendrite-free Zn deposition, high voltage output (>2.2 V) as well as wide-temperature adaptability from −40 to 80 °C, which is quite promising for grid-scale energy storage. Our work opens a new avenue for building high-rate low-cost batteries through coupling anion intercalation chemistry with multivalent metal anodes.