Lithium-based Electrolyte Research Articles

Unraveling lithium-ion intercalation in lead-free bismuth-based vacancy ordered halide perovskites supercapacitors

Halide perovskites have recently gained a lot of attention in energy storage applications because of their unique properties. The difficulty in getting high-performance supercapacitors requires the significant development and customization of electrode materials. This study explores vacancy-ordered lead-free halide perovskites with chemical formula A3B2X9 as electrode material for supercapacitors. Furthermore, we have tuned the X site (X = Br−, Cl−, I−) to see the effect of halide ions on supercapacitor performance. Due to high ionic mobility and BET surface area, Cs3Bi2I9 has a specific capacitance of ∼242 F/g and energy density of ∼140 Wh/kg; however, power density variation is almost the same for all samples, measured in three-electrode systems. We have performed the ex-situ XRD and FTIR to understand the structural changes before and after charging. XPS measurement shows the peak shifting before and after measurement in Lithium-based electrolytes. Further, we have fabricated double perovskite-based symmetric devices with gel electrolyte as a separator. The Cs3Bi2I9 device shows an areal energy density of ∼23 μWh/cm2, the highest among all halide perovskite-based supercapacitor devices reported to date. The flexible device on the S.S. substrate shows 79% and 82% capacitance retention up to 180° bending angle and 200 bending cycles, respectively.

Lithium ion Speciation in Cyclic Solvents: Impact of Anion Charge Delocalization and Solvent Polarizability.

The increasing demand for lithium batteries has triggered the search for safer and more efficient electrolytes. Insights into the atomistic description of electrolytes are critical for relating microscopic and macroscopic (physicochemical) properties. Previous studies have shown that the type of lithium salt and solvent used in the electrolyte influences its performance by dictating the speciation of the ionic components in the system. Here, we investigate the molecular origins of ion association in lithium-based electrolytes as a function of anion charge delocalization and solvent chemical identity. To this end, a family of cyano-based lithium salts in organic solvents, having a cyclic structure and containing carbonyl groups, was investigated using a combination of linear infrared spectroscopy and ab initio computations. Our results show that the formation of contact-ion pairs (CIPs) is more favorable in organic solvents containing either ester or carbonate groups and in lithium salts with an anion having low charge delocalization than in an amide/urea solvent and an anion with large charge delocalization. Ab initio computations attribute the degree of CIP formation to the energetics of the process, which is largely influenced by the chemical nature of the lithium ion solvation shell. At the molecular level, atomic charge analysis reveals that CIP formation is directly related to the ability of the solvent molecule to rearrange its electronic density upon coordination to the lithium ion. Overall, these findings emphasize the importance of local interactions in determining the nature of ion-molecule interactions and provide a molecular framework for explaining lithium ion speciation in the design of new electrolytes.

Sodium Polymer Electrolytes: A Review

Lithium-based electrolytes are, at least from a thermodynamic standpoint, the most suitable ion-transport materials for energy storage systems. However, lithium-based ionic conductors suffer from safety concerns, and the limited availability of lithium in the Earth’s crust is at the root of the need to consider alternative metal ions. Notably, sodium stands out as the sixth most-prevalent element; therefore, when considering mineral reserves, it as a very attractive candidate as an alternative to the status quo. Even if the specific energy and energy density of sodium are indeed inferior with respect to those of lithium, there is substantial economic appeal in promoting the use of the former metal in stationary energy storage applications. For these reasons, the promise of sodium is likely to extend to other commercial applications, including portable electronics, as well as hybrid and electric vehicles. Widely used organic liquid electrolytes, regardless of their chosen metal cation, are disadvantageous due to leakage, evaporation, and high flammability. Polymer electrolytes are acknowledged as the most effective candidates to overcome these obstacles and facilitate the advancement of next-generation energy storage applications. In this contribution, an in-depth and comprehensive review of sodium polymer electrolytes for primary and secondary batteries is proposed. The overarching goal was to gain insight into successful synthetic strategies and their implications for conduction parameters and conductivity mechanisms. The focus lies on solid, gel, and composite polymer electrolytes. Our hope is that the proposed discussion will be helpful to all operators in the field, whether in tackling fundamental research problems or resolving issues of practical significance.

Correction: Tuning aprotic solvent properties with long alkyl chain ionic liquid for lithium-based electrolytes

Correction for ‘Tuning aprotic solvent properties with long alkyl chain ionic liquid for lithium-based electrolytes’ by Tuanan C. Lourenço et al., J. Mater. Chem. A, 2022, 10, 11684–11701, https://doi.org/10.1039/D1TA10592B.

Fabrication of Li, Na and K electrolytes with doping elements for improved efficiency based on MOT and symmetry

This work is focused on finding a more effecient electrolyte to enhance the lithium-ion battery's overall characteristics and performance under Molecular Ortbital Theory (MOT) approach. As lithium-based electrolytes are now widely employed in all battery-operated portable devices, their use must be done with caution owing to a number of issues, including their toxicity, limited ionic conductivity, explosiveness, corrosiveness and hydrolysability creating harmful gasses. Using computational tools, a solution for these kinds of issues has been evaluated. The core idea is to simulate and evaluate by changing molecular symmetries. The molecular descriptors used include non-covalent interactions, band structure, density of states, electrostatic potential and fukui indices. Following our findings, a soft molecule with a smaller energy gap will be more polarizable and capable of charge transfer, making it more chemically reactive and less non-corrosivity than lithium hexafluoroarsenate (LiAsF6) and lithium hexafluorophosphate (LiPF6). For comparison, we also examined the electronic properties of electrolytes using first-principles calculations based on the DFT in the material design software MedeA® computational environment and also carried out Band structure and DOS calculation, which indicate the significance of band gap of between 1.41 to 2.91 eV. Since, soft molecules lead to good conductivity, chemically reactive and electron transport. A relative study with sodium and potassium-based electrolytes was also performed.

From the Irreversible Transformation of VO2 to V2O5 Electrochromic Films.

Since its discovery, electrochromism, known as the modulation of optical properties under an applied voltage, has attracted strong interest from the scientific community and has proved to be of significant utility in various applications. Although vanadium dioxide (VO2) has been a candidate for extensive research for its thermochromic properties, its intrinsic electrochromism has scarcely been reported so far. In this study, multi-electrochromism is described for VO2 thick films. Indeed, a VO2 opaque film, doctor bladed from homemade monoclinic VO2 powder, shows a pronounced color modulation from orange to green and blue associated with an amorphization-recrystallization phenomenon upon cycling in a lithium-based electrolyte. The strong memory effect allows us to follow the coloration mechanism by combining various ex situ and in situ characterizations addressing both structural and electronic aspects. Upon cycling, the multichromism of VO2 finds its origin in the transformation of VO2 into orange V2O5 upon oxidation, while in reduction, the blue lithiated state illustrates a mixed vanadium oxidation state.

Tuning aprotic solvent properties with long alkyl chain ionic liquid for lithium-based electrolytes

Lithium–metal batteries, such as Li–O2, are some of the most promising candidates for high-performance energy storage applications, however, their performance is still limited by the electrolyte instability.

Films of directionally oriented carbon nanotubes as counter electrodes for electrochromic devices

Connected displays are the salient nature of our e-connected society requiring high-quality electronic conductive materials integrated in smart devices. Herein, we highlight the use of carbon nanotubes (CNTs) not only as substitutes for ITO (In2O3:Sn) but mainly as a counter electrode for electrochromic devices (ECDs). Using a dry spinning process, conductive CNT films with directionally oriented tubes were successfully laid on polyethylene terephthalate (PET) flexible substrates. The CNTs were synthesized as vertically aligned spinnable arrays by chemical vapor deposition. The transparency and optical absorption properties were tuned by adjusting the number of CNT layers (L) within the film from light gray for 1L to dark black above 10L. The CNT films, showing pseudo-capacitive to capacitive behavior in lithium-based electrolytes, were further integrated in ECDs based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) active layers. The fabricated PET/ITO/PEDOT:PSS/electrolyte/CNT/PET device exhibited reproducible and clear color switching from light to dark blue with a coloration efficiency of 88 cm2 C−1. This study highlights novel architecture of ECDs using CNT-based films as conductive counter electrode.

Dual-cation electrolytes for low H2 gas generation in Li4Ti5O12//AC hybrid capacitor system

H2 gas generation with associated swelling using Li4Ti5O12 (LTO)-based hybrid capacitors upon high-voltage operation over 3.0 V has been a major challenge owing to catalytic reductive decomposition of solvent such as propylene carbonate (PC) at the Lewis-acid sites on the LTO surface. Herein, we report a method to suppress gassing behavior by adding spiro(1,1′)-bipyrrolidinium tetrafluoroborate (SBPBF4) to the lithium-based electrolyte [1 M lithium tetrafluoroborate (LiBF4) in PC]. The dual-cation (Li+/SBP+) electrolyte, which has previously been reported as the electrolyte composition used for rate-capability enhancement, reduced 35–50% volume of generated H2 compared to that for the single-cation (Li+) electrolyte under high-voltage floating conditions (3.5 V, 60 °C). This behavior was attributed to the LTO surface passivated by the Lewis-based layer via Hofmann elimination of SBP+. The concept of passivation of the LTO Lewis-acid site in the presence of SBP+ was further confirmed by applying alternative quaternary ammonium cations, such as tetraethylammonium (TEA+) and triethylmethylammonium (TEMA+), resulting in reduced H2 generation to the same level as that obtained using the SBP+-based dual-cation.

Probing Lithium-Ion Battery Electrolytes with Laboratory Near-Ambient Pressure XPS

In this article, we present Near Ambient Pressure (NAP)-X-ray Photoelectron Spectroscopy (XPS) results from model and commercial liquid electrolytes for lithium-ion battery production using an automated laboratory NAP-XPS system. The electrolyte solutions were (i) LiPF6 in EC/DMC (LP30) as a typical commercial battery electrolyte and (ii) LiTFSI in PC as a model electrolyte. We analyzed the LP30 electrolyte solution, first in its vapor and liquid phase to compare individual core-level spectra. In a second step, we immersed a V2O5 crystal as a model cathode material in this LiPF6 solution. Additionally, the LiTFSI electrolyte model system was studied to compare and verify our findings with previous NAP-XPS data. Photoelectron spectra recorded at pressures of 2–10 mbar show significant chemical differences for the different lithium-based electrolytes. We show the enormous potential of laboratory NAP-XPS instruments for investigations of solid-liquid interfaces in electrochemical energy storage systems at elevated pressures and illustrate the simplicity and ease of the used experimental setup (EnviroESCA).

On-Surface Self-Assembly of Stimuli-Responsive Metallo-Organic Films: Automated Ultrasonic Spray-Coating and Electrochromic Devices.

We demonstrate the on-surface formation of homogeneous and uniform electrochromic films via ultrasonic spray coating. This fully automated process is capable of fabricating metallo-organic films on transparent conducting oxides (TCOs) on glass or flexible poly(ethylene terephthalate) (PET) with surface areas of up to 36 cm2 and film thicknesses of half a micron. The assembly process involves alternatingly spray-coating dilute solutions of structurally well-defined iron polypyridyl ([Fe(mbpy-py)3]2+) complexes and bis(benzonitrile)palladium dichloride (Pd(PhCN)2Cl2) onto conductive substrates, where the latter palladium salt was used as the inorganic cross-linker. The on-surface self-assembled three-dimensional networks are intensely colored and were subsequently integrated into laminated electrochromic devices (ECDs) containing a lithium-based gel electrolyte. The ECDs retain their intense color in the ground state, having a Δ Tmax of 40-49% at λmax ≈ 600 nm, and can be operated for up to 1500 redox cycles. The fluorine-doped tin oxide counter electrode coated with poly(3,4-ethylene-dioxythiophene)polystyrene sulfonate (PEDOT:PSS) as a charge-storage layer resulted in these stable devices. A significant decrease in the potential window of Δ E ≈ 2.5 V was achieved by using a metal grid on PET as the counter electrode. The operation of the electrochromic films is diffusion-controlled, and the diffusion coefficients ( Df) reflect their molecular densities. During these studies, we found that ClO4- is a suitable counterion of the lithium-based electrolytes for optimal ECD performance.

Improved Cycling Performance of Intermetallic Anode By Minimized SEI Layer Formation

Alloy anodes including intermetallic anode, such as Si, Sn, Sb or Al, have been widely studied to replace the standard graphite-based anode, because these anode active materials theoretically have much higher specific capacity than the graphite anodes. The biggest challenge of the alloy anode is its cycleability. Huge volume expansion/shrinkage during the lithiation/delithiation process leads the pulverization of the active material particles resulting in loss of the electric contact among active in the electrode. Since the volume expansion/shrinkage also initiates formation/dissipation of electrode/electrolyte interphase, the SEI layer is supposed to have physical flexibility. However, the required physical properties of the SEI layer is not understood yet. We think the analogy of Mg-based system is useful, because the organohaloaluminate-based electrolyte solution of the Mg-based system does not form the typical SEI layer. In the present study, electrochemical properties of bismuth composite electrode are investigated in magnesium and lithium system. The bismuth composite electrode shows good cycleability in a magnesium half-cell with an organohaloaluminate electrolyte solution, while sever capacity decay is observed in a lithium system with a conventional carbonate-based electrolyte solution. In the carbonate-based electrolyte solution, the bismuth composite electrode shows low coulombic efficiency of < 90% due to the formation of solid electrolyte interphase (SEI) layer, while the high coulombic efficiency is maintained in the magnesium system. The comparison of the two system suggests that the formation of the SEI layer accelerates the capacity fading. Another lithium-based electrolyte solution: 2M LiBH4 in THF is proposed as a minimized SEI formation electrolyte solution. The LiBH4-based electrolyte solution shows excellent cycleability with high coulombic efficiency. A spectroscopic study using in situ FTIR proved that the LiBH4-based electrolyte solution does not form the typical thick SEI layer.

Double-Sided Electrochromic Device Based on Metal-Organic Frameworks.

Devices displaying controllably tunable optical properties through an applied voltage are attractive for smart glass, mirrors, and displays. Electrochromic material development aims to decrease power consumption while increasing the variety of attainable colors, their brilliance, and their longevity. We report the first electrochromic device constructed from metal organic frameworks (MOFs). Two MOF films, HKUST-1 and ZnMOF-74, are assembled so that the oxidation of one corresponds to the reduction of the other, allowing the two sides of the device to simultaneously change color. These MOF films exhibit cycling stability unrivaled by other MOFs and a significant optical contrast in a lithium-based electrolyte. HKUST-1 reversibly changed from bright blue to light blue and ZnMOF-74 from yellow to brown. The electrochromic device associates the two MOF films via a PMMA-lithium based electrolyte membrane. The color-switching of these MOFs does not arise from an organic-linker redox reaction, signaling unexplored possibilities for electrochromic MOF-based materials.

Oxygen Redox Reaction in Lithium-based Electrolytes: from Salt-in-Solvent to Solvent-in-Salt

Electrolytes are key components of Li/O2 batteries. The ionic liquid-like structure and good electrochemical and thermal stability of solvent-in-salt electrolytes make them of great interest for lithium batteries. Solutions of lithium bis(trifluoromethanesulfonyl)imide in tetraethylene glycol dimethyl-ether with molar ratios ranging from 1:9 to 1:0.9 are here investigated. A voltammetric study of oxygen redox reaction in presence of different concentrations of salt, from salt-in-solvent to solvent-in-salt solutions, is reported here for the first time along with a novel luminescence method for the evaluation of O2 solubility. The results indicate that superconcentrated solutions favor the solution formation mechanism of Li2O2 during discharge which in turn is beneficial for battery cycling stability. Despite the higher viscosity of solvent-in-salt solutions than conventional electrolytes, O2 solubility is improved at the highest salt concentrations. These findings contribute to understand electrochemical processes in solvent-in-salt solutions for Li/O2 and next generation metal-based batteries.

Lithium n-Doped Polyaniline as a High-Performance Electroactive Material for Rechargeable Batteries.

The discovery of conducting lithium-doped polyaniline with reversible redox chemistry allows simultaneous unprecedented capacity and stability in a non-aqueous Li battery. This compound (lithium emeraldinate) was synthesized by lithium-proton exchange on the emeraldine base in an anhydrous lithium-based electrolyte. A combination of UV/Vis-NIR spectroelectrochemistry, XPS, FTIR, and EQCM characterization allowed a unified description of the chemical and electrochemical behavior, showing facile charge delocalization of the doped states and the reversibility of the redox processes in this form of polyaniline. From a practical point of view, lithium emeraldinate behaves as a high-capacity organic active material (230 mAh g-1 ) that enables preparation of relatively thick composite electrodes with a low amount of carbon additives and high energy density (460 Wh kg-1 ). Concomitantly, at 1C rate, 400 cycles were achieved without significant capacity loss, while the coulombic efficiency is greater than 99 %.

Polyol Synthesis of Ti-V2O5 Nanoparticles and Their Use as Electrochromic Films.

Herein, the successful synthesis of Ti-doped vanadium pentoxide from a polyol process is reported. A high Ti concentration (up to 8.5 mol % of the total metallic content) can be inserted in vanadium oxide thanks to the synthesis route leading to nanometric crystallites. X-ray diffraction patterns were refined showing the insertion of the titanium ions inside the free pentacoordinated sites in opposition to the vanadium square pyramidal sites. This crystal organization was shown in good agreement with the ab initio positioning performed from valence calculation. The nanoparticles, NPs, of Ti-doped V2O5 compounds were characterized as electrochromic materials. Films elaborated from a dip-coating process from oxide particle suspensions exhibited three distinct colorations during the redox cycling in lithium-based electrolyte. These colors were associated with three distinct oxidation states for the vanadium ions: +III (blue), +IV (green), and +V (orange). The morphology of the films was shown to drastically impact the electrochromic performances in terms of electrochemical capacity and stability.

Understanding Electrode-Electrolyte Solution Interactions Between TiO2 Nanotube Electrode and Nonaqueous Electrolytes for Sodium-Ion Batteries

Sodium-ion battery technology presents a promising sustainable alternative to the current dominating lithium-ion battery technology due to its low cost associated with its high earth abundance. It has been shown that the interfacial chemistry between anodes and sodium-based or lithium-based electrolytes have markedly different effect even when using the same solvent. It is important to investigate sodium-based electrolytes and to elucidate the mechanisms of electrode and electrolyte interactions. The design and development of next generation electrolytes for sodium-ion batteries is catered towards the improved performance based on evaluation of thermodynamic /transport properties, chemical and electrochemical stability, thermal stability and interfacial chemistry. In this work, we have investigated the electrochemical properties of TiO2 nanotube electrode in various electrolytes containing different solvent mixtures (cyclic, acyclic carbonates) with NaClO4 1 salt and NaPF6 salt and have found that the interaction between the TiO2NT electrode and the nonaqueous electrolytes plays a critical role in the charging/discharging processes. In addition, we have conducted fundamental studies of the chosen sodium-based electrolytes on their chemical stability, thermal stability and electrochemical stability.

Synthesis, Structure, and Properties of the New Intercalation Cathode Material MoO2.8F0.2

The widespread adoption of multivalent batteries is hampered by the lack of stable, reliable, high voltage cathodes that can reversibly intercalate divalent cations. In lithium-based systems, molybdenum trioxide has been studied for several years as a high capacity cathode material. Although its voltage is lower than other systems, e.g. V2O5, it has advantages including crystallographic stability on cycling. A key issue that is believed to limit its performance is that, as a d0 metal oxide, it has limited electronic conductivity at top of charge.1 In this poster we will be discussing the role of fluoride incorporation into the layered charged cathode MoO3 and its effect on the materials physical properties. Utilizing synthetic methodologies developed in our lab we have studied the fluoride solubility in the host material as a way to induce electronic conductivity across the whole range of use. We have shown that the maximum fluoride incorporation in the material yields a stoichiometry of MoO2.8F0.2. Incorporation above this value results in isolation of the perovskite phase MoO2.6F0.4. We have evaluated the material using multiple intercalating cations and compared it to the undoped parent material. While the electrochemical activity of the material using a lithium-based electrolyte is similar, remarkable differences have been observed when Mg is used as the cation. While the undoped material has little or no activity, the fluorinated materials shows excellent cycleability and structural reversibility.2

Electrochromism of non-stoichiometric NiO thin film: as single layer and in full device

Electrochromic properties, known as a reversible modulation of the optical properties under an applied voltage, of NiO thin films are discussed in respect of the film stoichiometry. Using radio-frequency magnetron sputtering, non-stoichiometric “NiO” thin films of good crystallinity were grown at room temperature from low oxygen partial pressure [i.e., above 2 % P(O2/Ar + O2)]. A further increase in oxygen partial pressure leads to conductive brownish films containing a large amount of Ni3+. 2 %-Ni1−x O thin films exhibit significant EC performance in lithium-based electrolyte with a transmittance modulation of 25 %. If it is generally accepted that this optical modulation is due to an insertion of small cations, the presence of additional surface phenomena is also shown. The cycling of full device, based on the association of WO3 and “NiO” in temperature up to 60 °C and down to −35 °C confirms expected increase and decrease in capacity while surprisingly the optical switch from a transparent to a neutral gray color appears slightly modified.

Electrochemical Li+ insertion capabilities of Na4−xCo3(PO4)2P2O7 and its application to novel hybrid-ion batteries

Electrochemically Na+-extracted Na4−xCo3(PO4)2P2O7 exhibits both Li+ and Na+ insertion capabilities. Given these compatibilities, novel hybrid-ion batteries were demonstrated by combining a Na4Co3(PO4)2P2O7 positive electrode and Li4Ti5O12 negative electrode in a lithium-based electrolyte.