Electrolytes and interphases in Li-ion batteries and beyond.

Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

A review of electrolyte materials and compositions for electrochemical supercapacitors

Energy-storage technologies, including electrical double-layer capacitors and rechargeable batteries, have attracted significant attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and “load leveling” of renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double-layer capacitors requires a step change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning lithium batteries and electric double-layer capacitors.

Challenges Facing Lithium Batteries and Electrical Double‐Layer Capacitors

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties becom...

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices

The ever-growing demand for advanced rechargeable lithium-ion batteries in portable electronics and electric vehicles has spurred intensive research efforts over the past decade. The key to sustaining the progress in Li-ion batteries lies in the quest for safe, low-cost positive electrode (cathode) materials with desirable energy and power capabilities. One approach to boost the energy and power densities of batteries is to increase the output voltage while maintaining a high capacity, fast charge–discharge rate, and long service life. This review gives an account of the various emerging high-voltage positive electrode materials that have the potential to satisfy these requirements either in the short or long term, including nickel-rich layered oxides, lithium-rich layered oxides, high-voltage spinel oxides, and high-voltage polyanionic compounds. The key barriers and the corresponding strategies for the practical viability of these cathode materials are discussed along with the optimization of electrolytes and other cell components, with a particular emphasis on recent advances in the literature. A concise perspective with respect to plausible strategies for future developments in the field is also provided.

High-voltage positive electrode materials for lithium-ion batteries

The electrochemical behavior of organo-fluorine compounds with antioxidation ability has been investigated. Oxidation currents of fluorine-compound-containing ethylene carbonate (EC)/diethyl carbonate (DEC) solutions were much smaller than those of EC/ DEC and EC/DEC/propylene carbonate (PC) at potentials higher than 6 V vs Li/Li + . Electrochemical reduction of fluorine compounds started at ca. 2 V vs Li/Li + , higher than those for EC, DEC, and PC. However the first coulombic efficiencies for natural graphite electrodes in fluorine-compound-containing EC/DEC mixtures were nearly the same as those in EC/DEC without an increase in irreversible capacities. Furthermore the first coulombic efficiencies in fluorine-compound-containing EC/DEC/PC mixtures were much larger than those in EC/DEC/PC itself. The results show that the fluorine compounds used in the present study can be used as nonflammable solvents for lithium ion batteries.

https://iopscience.iop.org/article/10.1149/1.3111904/pdf

Electrochemical Behavior of Nonflammable Organo-Fluorine Compounds for Lithium Ion Batteries

Differential scanning calorimetry study demonstrated that mixing of fluoro-ethers and fluoro-carbonates improved the thermal stability of 0.67 mol/L LiClO 4 ―ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PC) (1:1:1 by volume). The oxidation currents were smaller in the fluorine compound-mixed electrolyte solutions than in 0.67 mol/L LiClO 4 ―EC/DEC/PC, which also shows a high stability of the fluorine compound-mixed electrolyte solutions against electrochemical oxidation. Electrochemical reduction of fluorine compounds took place at the higher potentials than EC, DEC, and PC, as suggested by the highest occupied molecular orbital and lowest unoccupied p-molecular orbital energies of the fluorine compounds. However, charge/discharge experiments using natural graphite (NG) electrodes showed that the fluorine compounds increased first coulombic efficiencies due to the quick formation of the solid electrolyte interphase on NG in PC-containing solvents.

Thermal Stability and Electrochemical Properties of Fluorine Compounds as Nonflammable Solvents for Lithium-Ion Batteries

There is provided a non-aqueous electrolytic solution assuring good solubility of an electrolyte salt and having enough cell characteristics (charge and discharge cycle characteristic, discharge capacity, and the like), and the non-aqueous electrolytic solution comprises a solvent for dissolving an electrolyte salt comprising (A) at least one fluorine-containing solvent selected from the group consisting of fluorine-containing ethers and fluorine-containing carbonates, (B) a non-fluorine-containing cyclic carbonate and (C) a chain ester represented by the formula (C): R1COOR2, wherein R1 is an alkyl group having 2 to 4 carbon atoms; R2 is an alkyl group having 1 to 4 carbon atoms or a fluorine-containing alkyl group having 1 to 4 carbon atoms, and (II) an electrolyte salt.

Non-aqueous electrolytic solution

Disclosed is a nonaqueous electrolyte solution containing a solvent (I) for dissolving an electrolyte salt, and an electrolyte salt (II). The solvent (I) for dissolving an electrolyte salt contains a fluorine-containing solvent (A) selected from the group consisting of fluorine-containing ethers, fluorine-containing esters and fluorine-containing carbonates, a non-fluorine cyclic carbonate (B), and a non-fluorine chain carbonate (C), and further contains not more than 5% by mass of a surface active agent (D) relative to the total of the solvent (I). Consequently, phase separation does not occur in this nonaqueous electrolyte solution even at low temperatures, and the nonaqueous electrolyte solution has excellent incombustibility (flame retardancy), excellent heat resistance, high solubility of the electrolyte salt, improved battery capacity, excellent rate characteristics, and excellent charge/discharge cycle characteristics.

Nonaqueous electrolyte solution

The objective of the present invention is to provide an electrolyte solution with which an electrochemical device or module having excellent storage characteristics in high temperatures can be obtained. The present invention is an electrolyte solution including a solvent and an electrolyte salt, said electrolyte solution being characterized by including at least one compound (α) selected from the group consisting of an amine (A) represented by general formula (A) and an amide (B) represented by general formula (B), wherein the content of the compound (α) in the electrolyte solution is 0.001-20ppm. (In the formula (A), R 1 and R 2 can be the same or different, and are C1-7 alkyl groups, and Rf 1 is a C1-7 fluorinated alkyl group.) (In the formula (B), R 3 , R 4 , and R 5 can be the same or different, and are C1-7 alkyl groups.)

Akiyoshi Yamauchi

Papers

Electrochemical Behavior of Nonflammable Organo-Fluorine Compounds for Lithium Ion Batteries

Thermal Stability and Electrochemical Properties of Fluorine Compounds as Nonflammable Solvents for Lithium-Ion Batteries

Non-aqueous electrolytic solution

Nonaqueous electrolyte solution

Electrolytic solution, electrochemical device, lithium ion secondary battery, and module