Electrochemical Properties Of Electrolytes Research Articles

A comprehensive study of affordable “water-in-salt” electrolytes and their properties

The search for alternative electrolytes has been extremely topical in recent years with the “water-in-salt” electrolyte, especially, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) coming to the fore in the context of high-voltage electrolytes. However, “water-in-LiTFSI” exhibits ultra-high cost and low ionic transport when compared with the aqueous lithium-halide, -nitrate as well as -sulphate salts (quoted as LiX). This work rediscovered the properties of a “water-in-salt” (LiX electrolytes) made from a variety of concentration from 1 m to saturated conditions. The changes of physical properties e.g., viscosity, pH, conductivity, density, and temperature during mixing were then reported. The electrochemical properties of electrolyte were tested using carbon-based materials (YEC-8A) as a model system (three electrode configuration), and the finding was then expanded to a coin cell supercapacitor for benchmarking the performance per cost unit. It has been found that the use of highly concentrated LiX electrolytes does not always enhance the potential window. LiBr and LiI shown the redox properties while increasing the concentration can speed up the redox process (voltage remains unchanged). Using superconcentrated LiCl can slightly expand the potential window; however, corrosion is the main task to be addressed. Besides, voltage expansion of LiNO3 is found to be approximately 2.2 V, which is comparable to LiTFSI. The breakdown cost of the electrolyte also shows that LiTFSI exhibits the lowest energy density per cost unit (dollars), while LiNO3 provides the most feasible cost in term of power density. We then marked that the electrolytes such as LiBr and LiI can be used as redox additive electrolytes. This work also shows the fundamental insight into the physical and electrochemical properties of LiX for possible alternative use as a cheap “water-in-salt” electrolyte in energy storage apart from LiTFSI.

Preparation and electrochemical properties of a ceramic solid electrolyte with high ionic conductivity, Li1.3Al0.3Ti1.7(PO4)3

The emergence of lithium-ion solid electrolytes greatly increases the safety risk of liquid electrolytes. Among the many solid electrolytes, aluminum-doped Li1.3Al0.3Ti1.7(PO4)3(LATP) has become a research hotspot due to its high ionic conductivity and good air stability. However, the traditional high-temperature sintering process has the problems of lithium volatilization and secondary phase formation. Therefore, it is very difficult to prepare high-quality LATP solid electrolytes. The X-ray diffraction pattern and analysis showed that the LATP samples prepared in this paper showed rhombohedral structure and could be indexed by the R3c space group, and a new method of excess lithium compensation sintering was proposed, in which lithium compensation (LiNO3) could well reduce the impact of lithium volatilization. It can be used as a sintering additive to promote the sintering densification of LATP. In this paper, the optimal sample for sintering at 900°C was determined by measuring the microstructure and electrochemical properties of the electrolyte, and lithium doping was studied. The LATP solid electrolyte with 10 wt% lithium doped has a conductivity of 7.2× 10−4 S/cm and a low activation energy (0.278 eV). Its mechanical properties (elastic modulus and hardness) are the best, which are 103.024 GPa and 8.053 GPa, respectively, and the value of its elastic modulus is much greater than that of lithium metal shear modulus of 4.25 GPa, which can effectively inhibit the growth of lithium dendrites. And the magnitude of the grain boundary conductivity and particle size of the lithium-doped sample correspond to the dielectric constant results.

Low-Temperature Properties of the Sodium-Ion Electrolytes Based on EC-DEC, EC-DMC, and EC-DME Binary Solvents

Sodium-ion batteries are a promising class of secondary power sources that can replace some of the lithium-ion, lead–acid, and other types of batteries in large-scale applications. One of the critical parameters for their potential use is high efficiency in a wide temperature range, particularly below 0 °C. This article analyzes the phase equilibria and electrochemical properties of sodium-ion battery electrolytes that are based on NaPF6 solutions in solvent mixtures of ethylene carbonate and diethyl carbonate (EC:DEC), dimethyl carbonate (EC:DMC), and 1,2-dimethoxyethane (EC:DME). All studied electrolytes demonstrate a decrease in conductivity at lower temperatures and transition to a quasi-solid state resembling “wet snow” at certain temperatures: EC:DEC at −8 °C, EC:DMC at −13 °C, and EC:DME at −21 °C for 1 M NaPF6 solutions. This phase transition affects their conductivity to a different degree. The impact is minimal in the case of EC:DEC, although it partially freezes at a higher temperature than other electrolytes. The EC:DMC-based electrolyte demonstrates the best efficiency at temperatures down to −20 °C. However, upon further cooling, 1 M NaPF6 in EC:DEC retains a higher conductivity and lower resistivity in symmetrical Na3V2(PO4)3-based cells. The temperature range from −20 to −40 °C is characterized by the strongest deterioration in the electrochemical properties of electrolytes: for 1 M NaPF6 in EC:DMC, the charge transfer resistance increased 36 times, and for 1 M NaPF6 in EC:DME, 450 times. For 1 M NaPF6 in EC:DEC, the growth of this parameter is much more modest and amounts to only 1.7 times. This allows us to consider the EC:DEC-based electrolyte as a promising basis for the further development of low-temperature sodium-ion batteries.

Comparable Investigation of Phosphorus-Based Flame Retardant Electrolytes on LiFePO4 Cathodes

Improving the flame retardant and electrochemical properties of electrolytes is of great significance to enhance the safety of lithium-ion batteries (LIBs). In this work, the effect of cresyl diphenyl phosphate (CDP), dimethyl methyl phosphonate (DMMP), trimethyl phosphate (TMP) and triphenyl phosphate (TPP) as flame retardant additives in the standard electrolyte on the performance of LiFePO4/Li cell are comprehensively studied. The results show that when the mass fraction of flame retardant is less than 20%, the purpose of flame retardant can be achieved in the electrolyte. When the cells without and with 20 wt% of CDP, DMMP, TMP, and TPP additives are, respectively, their capacity retentions are 80, 46, 82, 84, and 57% after 100 cycles at 0.5C. According to characterization analysis, DMMP and TMP can facilitate the formation of stable interface films on cathode and subsequently improve the battery performance. Compared with expensive or complicated synthetic flame retardants, conventional flame retardants like CDP, DMMP, TMP, and TPP have great potential for application in electrolytes to improve the safety of LIBs. This work can provide useful scientific research and industry in the study of phosphorus-based flame retardant electrolytes.

High‐Voltage Aqueous Mg‐Ion Batteries Enabled by Solvation Structure Reorganization

AbstractHerein, an eco‐friendly and high safety aqueous Mg‐ion electrolyte (AME) with a wide electrochemical stability window (ESW) ≈3.7 V, containing polyethylene glycol (PEG) and low‐concentration salt (0.8 m Mg(TFSI)2), is proposed by solvation structure reorganization of AME. The PEG agent significantly alters the Mg2+ solvation and hydrogen bonds network of AMEs and forms the direct coordination of Mg2+ and TFSI‐, thus enhancing the physicochemical and electrochemical properties of electrolytes. As an exemplary material, V2O5 nanowires are tested in this new AME and exhibit initial high discharge/charge capacity of 359/326 mAh g‐1 and high capacity retention of 80% after 100 cycles. The high crystalline α‐V2O5 shows two 2‐phase transition processes with the formation of ε‐Mg0.6V2O5 and Mg‐rich MgxV2O5 (x ≈1.0) during the first discharge. Mg‐rich MgxV2O5 (x ≈1.0) phase formed through electrochemical Mg‐ion intercalation at room temperature is for the first time observed via XRD. Meanwhile, the cathode electrolyte interphase (CEI) in aqueous Mg‐ion batteries is revealed for the first time. MgF2 originating from the decomposition of TFSI‐ is identified as the dominant component. This work offers a new approach for designing high‐safety, low‐cost, eco‐friendly, and large ESW electrolytes for practical and novel aqueous multivalent batteries.

Interplay between Mechanical and Electrochemical Properties of Block Copolymer Electrolytes and its Effect on Stability against Lithium Metal Electrodes

We have studied the cycle life of two polyhedral oligomeric silsesquioxane-b-poly(ethylene oxide)-b-polyhedral oligomeric silsesquioxane (POSS-PEO-POSS) block copolymer electrolytes differing primarily in molecular weights and composition using lithium/polymer/lithium symmetric cells. The higher molecular weight electrolyte, labeled H, has a higher storage modulus, G el . However, the volume fraction of the conducting phase in the low molecular weight electrolyte, labeled L, is higher and this leads to a four-fold increase in limiting current density, i L. Measurement of ionic conductivity provides insight into the reason for the observed differences in limiting current density. The average lifetime of symmetric cells with electrolyte L was slightly higher than that of cells with electrolyte H. The combined effect of mechanical and electrochemical properties of electrolytes on the stability of lithium electrodeposition was quantified by examining two dimensionless parameters, i/i L and G el /G Li , introduced in the theory developed by Barai and Srinivasan [Phys. Chem. Chem. Phys., 19, 20493–20505 (2017)]. This theory predicts the regime of stable lithium electrodeposition as a function of these two parameters. Despite large differences in G el and i L between the two electrolytes, we show that similar cell lifetimes are consistent with the theoretical predictions of unstable lithium electrodeposition without resorting to any adjustable parameters.

Preparation and Characterization of Lithium Ion Conductive Organic/Inorganic Composite Solid Electrolyte.

The purpose of this study was to improve the ionic conductivity and physical properties of a polymer electrolyte by complexing it with ceramic particles. First, a polymer/ceramic composite solid electrolyte was prepared by synthesizing a super porous silica aerogel powder and adding it to a slurry containing a polyethylene oxide (PEO)-based polymer electrolyte; then, the electrochemical properties of electrolyte of different compositions were confirmed. PEO and polymethyl methacrylate (PMMA) were copolymerized, the optimum ratio of lithium salt, plasticizer, and silica aerogel was determined, and ion conductivity of the composite electrolyte was improved. When the EO:Li ratio was 10:1, the glass transition temperature was the lowest, and the room-temperature ion conductivity was improved to 3.0 × 10-5 S/cm. As a result of XRD and thermal analysis, it was confirmed that the stability and durability of the electrolyte interface can also be improved by complexation of the polymer electrolyte with ceramic particles.

Research progress on electrochemical properties of electrolyte and its interphase

Electrolyte not only plays the role of conducting ions in lithium ion battery, but also the thin layer electrolyte formed on the electrode surface determines the stability of electrode/electrolyte interface to a large extent, thus affecting the cycling stability, rate performance and safety of the battery. The successful commercialization and widespread application of lithium ion battery is closely related to the solid electrolyte interface film formed by the decomposition of electrolyte on the electrode surface. In this paper, the electrochemical stability and decomposition mechanism of the interface electrolyte are briefly reviewed, aiming to draw more scientists' attention to the electrolyte and its interfacial properties.

Comparison of LiTDI and LiPDI salts and influence of their perfluoroalkyl side-chain on association and electrochemical properties in triglyme

For the first time, the effect of minor structural changes to the electrolyte salt on solution properties is investigated experimentally. It was achieved by decomposition of the overall changes into individual components. It allowed to obtain information on the contradicting effects influence on the final result. This study is focused on comparison of two lithium salts: lithium 4,5-dicyano-2-(trifluoromethyl) imidazolide (LiTDI) and lithium 4,5-dicyano-2-(pentafluoroethyl) imidazolide (LiPDI). LiTDI is a very promising salt for lithium-ion battery application. PDI− anion differs from TDI− only in length of perfluorinated alkyl chain. Triethylene glycol dimethyl ether (triglyme) solutions of both salts in a wide range of concentrations were prepared. Triglyme was chosen as a solvent due to number of oxygen atoms which allows for fulfilment of lithium cation coordination sphere. Use of such similar salts in a model system allows us to find the correlation between salt structure and properties of electrolyte. Conductivity, viscosity, lithium transference number, thermal properties and FTIR spectra were measured for all solutions. Ionic fractions were also estimated by Fuoss-Kraus formalism. Obtained results showed that electrochemical properties of electrolyte are result of several opposing factors. Transference numbers are mostly dependent on association. We have also observed interesting correlation between thermal properties and conductivity.

High ionic conductivity Y doped Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

Li1.3Al0.3Ti1.7(PO4)3 is regarded as one of the most promising solid electrolytes for all solid state lithium ion batteries (ASSLIBS). However, its grain boundary conductivity is still low, which reduces the total conductivity of electrolyte. In this work, in order to further improve the electrical conductivity of Li1.3Al0.3Ti1.7(PO4)3, a series of Y doped Li1.3Al0.3-xYxTi1.7(PO4)3 (x = 0, 0.025, 0.05, 0.075 and 0.15) solid electrolytes were synthesized using a modified solid state method. Effects of Y doping content on morphology, phase and electrical conductivity of Li1.3Al0.3Ti1.7(PO4)3 electrolyte materials were systematically investigated. All synthetic electrolyte powders show Nasicon-like structure, well-shaped polyhedral morphology as well as good crystallinity. Y dopant content has a great influence on electrochemical properties of electrolytes. The high total conductivity of 7.8 × 10−4 S/cm at room temperature and a low activation energy of 0.17 eV is obtained for the electrolyte with the Y doping content of 0.075 due to the increasing of grain boundary conductivity, and its electrical conductivity is about 2 times larger than that of the undoped electrolyte. The excellent electrochemical performance is mainly attributed to high electrolyte density which results from the good sintering property of electrolyte materials as well as the existence of YPO4 phase at grain boundaries. Additionally, this electrolyte has a negligible electronic conductivity. These results suggest that Y doped Li1.3Al0.3Ti1.7(PO4)3 can be used as an alternative solid electrolyte for all solid state lithium ion batteries.

Effects of Li6.75La3Zr1.75Ta0.25O12 on chemical and electrochemical properties of polyacrylonitrile-based solid electrolytes

Solid polymer electrolytes show great application potential in the next-generation all-solid-state Li-ion batteries due to its safety, electrochemical stability, and easy-processing feature. However, low ionic conductivity of solid polymer electrolytes hinders their commercialization. Currently, dispersing ceramic fillers in polymer electrolytes has been proved to be a promising approach to address this issue. Herein, we introduce Li6.75La3Zr1.75Ta0.25O12 fillers into polyacrylonitrile-LiClO4 matrix and study the effects of Li6.75La3Zr1.75Ta0.25O12 on chemical and electrochemical properties of the polyacrylonitrile-based electrolytes. The addition of Li6.75La3Zr1.75Ta0.25O12 triggers the cyclization and segmentation of polyacrylonitrile chains, which improves the mechanical strength and thermal stability of the electrolytes. The effects of Li6.75La3Zr1.75Ta0.25O12 on the electrochemical properties of the electrolytes are thoroughly investigated. The polyacrylonitrile-based electrolyte with 20 wt% Li6.75La3Zr1.75Ta0.25O12 fillers shows a high ionic conductivity of 2.2 × 10−4 S cm−1 at 40 °C, a wide electrochemical window of 4.9 V, and much improved Li+ transference number and cycling stability in a Li||Li symmetric cell. In addition, a solid-state LiFePO4||Li full cell is assembled and tested at room temperature, demonstrating the applicability of polyacrylonitrile-based electrolytes in all-solid-state batteries.

Breakthrough in Increasing Li-Ion Battery Energy and Safety, and Reducing Cost. Synergistic Effect of Novel Nanomaterials, Technology, Equipment for Production, and Non-Destructive Method of the Testing

Enerize Li-Ion batteries technologies deliver higher energy and safety, while have a lower cost using Enerize silicon based binder free anode, binder free cathodes, solid inorganic electrolyte formulation, innovative equipment for thin film batteries production, and manufacturing technologies High energy silicon – graphite composite anodes are fabricated via a proprietary method of gas detonation deposition, do not require a polymer binder. The method and equipment for fabricate the anode based on Si-graphite composition ensure high level of the adhesion between composition and current collector, and cohesion between the particles of silicon and graphite. As a result, anode has high energy and stability during cycling. During presentation will be presented results of the results of evaluation of the dynamics of changing the diffusion coefficients of lithium cations in the solid phase of the anode material, and the change of the kinetic parameters of the electrochemical reaction during cycling Novel vitreous high ionic conductivity solid inorganic electrolyte with high operating rage of the temperature, up to 300° C, enables new design of lithium batteries, including micro- & macro-batteries, with safe charge/cycling, wide operating temperature range, and flexible formats. Enerize's solid electrolyte has high level of chemical stability in contact with electrode materials, and electrochemical stability in a wide range of working potentials (up to 5.0 Volts). Key innovating methods and equipment for thin film deposition are based on the Gas Discharge Electron Gun with a Cold Cathode, and Gas Detonation Deposition, which provide the high rate deposition of thin layers of electrode materials and solid electrolytes with predetermined properties. Non-destructive non-contact electromagnetic, ultrasonic, holographic interferometry, gas discharge visualization, and combined methods and equipment developed by Enerize, are innovative tools for evaluation, control and maintenance of high quality and reliability of initial materials, including next generation materials, semi-product, final product, and technologies during Li-ion battery manufacturing, including in-line control During the presentation we will discuss: a) correlation between composition, structure and electrochemical properties of electrolyte and electrodes, b) equipment for high rate deposition of thin layers of electrode materials and solid electrolytes with predetermined structural, morphological, and electrochemical properties. Synergetic effect of new materials, technologies and equipment for thin film deposition reduces costs, increases productivity of battery fabrication, and provides reliability and high performance of batteries. Areas of applications of solid state batteries include: electric vehicle; aerospace related equipment; hybrid systems batteries / solar cells; oil & gas drilling, and deep

Electrode and electrodeless impedance measurement for determination of orange juices parameters

AbstractElectrical impedance spectroscopy (EIS) is a non-destructive, rapid and real-time measurement method which does not require special high-tech measurement devices and can be applied to food quality assessment. This method is rapid, effective and affords low-cost investigation of the product. The conventional EIS method requires a set of metal electrodes in direct contact with the medium to be measured. The complicated electrochemical processes on the electrodes-electrolyte interface could substantially affect the value of the impedance measured. The present study sought to explore the possibilities of using the impedance method for quality control in orange juices, to introduce the electrodeless method of electrolyte impedance measurement and to compare this with the conventional impedance methods. The electrical properties of the orange juices were described with the help of an equivalent circuit. An equivalent circuit was designed with constant phase element approximation. The values of the equivalent circuit components were fitted using a non-standard algorithm inspired by the behaviour of actual ant colonies. Implementing the electrodeless method obviated the electrodes phenomena effects and the behaviour of the electrolyte is similar to inductance. The proposed electrodeless method is generally applicable to measuring the electrochemical properties of electrolytes.

Preparation and characterization of epoxy/carbon fiber composite capacitors

Capacitors based on structural carbon fiber electrodes and epoxy‐based gel polymer electrolyte have been fabricated. The electrochemical properties of electrolytes and capacitors were evaluated by linear sweep voltammetry, cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. Surface modification of carbon fibers was carried out by oxidation, and the structural and surface characteristics of carbon fibers were investigated by scanning electron microscope, Brunauer–Emmet–Teller, and Boehm titration. The results showed that the electrochemical stability window of the electrolyte reached 2.75 V and the ionic conductivity reached the order of 10−5 S/cm at room temperature. Surface modification of carbon fiber by oxidation can enlarge fiber area and strengthen fiber chemical activity, as well as its energy storage ability. The specific capacitance of epoxy/carbon fiber composite capacitor was obtained as high as 3.0 F/g with good cycling performance. POLYM. COMPOS., 36:1447–1453, 2015. © 2014 Society of Plastics Engineers

Characterization of low-flammability electrolytes for lithium-ion batteries

In an effort to develop low-flammability electrolytes for a new generation of Li-ion batteries, we have evaluated physical and electrochemical properties of electrolytes with two novel phosphazene additives. We have studied performance quantities including conductivity, viscosity, flash point, and electrochemical window of electrolytes as well as formation of solid electrolyte interphase (SEI) films. In the course of study, the necessity for a simple method of SEI characterization was realized. Therefore, a new method and new criteria were developed and validated on 10 variations of electrolyte/electrode substrates. Based on the summation of determined physical and electrochemical properties of phosphazene-based electrolytes, one structure of phosphazene compound was found better than the other. This capability helps to direct our further synthetic work in phosphazene chemistry.