Carbonate-containing liquid electrolytes

Carbonate-containing liquid electrolytes are primarily chosen for their ability to dissolve lithium salts and their relatively low viscosity (which facilitates Li-ion diffusion between electrodes). Their flammability has in part led to interest in the use of room-temperature ionic liquids (ILs) as replacements. ILs can potentially operate in a higher voltage window relative to carbonates and also have the added benefit of being more thermally stable and having low vapor pressure. The main drawback of this class of compounds is a high viscosity. Additionally, carbonates may have to be introduced at certain voltages to form a suitable SEI for operation. 

As already mentioned, salt-containing liquid solvents are typically used as electrolytes. The most prominent example is LiPF6 as a conductive salt, dissolved in a 1 1 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) as 1 molar solution. It should be mentioned that this electrolyte is not thermodynamically stable in contact with lithium or, for example, LiC6. Its success comes from the fact that it forms an extremely stable passivation layer on top of the electrode, the so-called solid-electrolyte interface (SEI) [35], Key properties of such SEI layers are high Li+ and very low e conductivity - that is, they act as additional electrolyte films, where the electrode potential drops to a level the liquid electrolyte can withstand [36],... 

Fuel cells can use several kinds of fuel, including natural gas and petroleum products. However, these are fossil fuels that produce carbon dioxide, an undesirable byproduct, when oxidized. Another drawback of common fuel cells is that they operate at temperatures from 200°C to 1000°C, and some contain hot, caustic, liquid electrolyte. 

For transportation applications, such as automobiles and buses, the liquid electrolyte is replaced with a solid electrolyte-polytetrafluoroethylene containing pendent sulfonated fluoroethylene groups. Water is absorbed onto the sulfonated side chains, hydrogen ions are weakly attracted and are able to move from site to site, creating a weak acid. With an electrode structure consisting of a carbon-supported platinum... 

The calculators, electronic watches, personal music players that are so familiar to us are all powered by small, efficient dry cell batteries. They are called dry cells because they do not contain a liquid electrolyte. The common dry cell battery was invented more than 100 years ago by George Leclanche (1839-1882), a French chemist. In its acid version, the dry cell battery contains a zinc inner case that acts as the anode and a carbon (graphite) rod in contact with a moist paste of solid Mn02, solid NH Cl, and carbon that acts as the cathode (see Figure 18.4). The half-cell reactions are complex but can be approximated as follows ... 

Fig.l compares the in vivo performance of oxygen and carbon dioxide electrodes with a non-aqueous, solid polymer electrolyte with electrodes containing a conventional liquid electrolytes. These electrodes have been operating for several weeks with virtually unaltered sensitivity. 

A reversible lithium-air system was first implemented on a laboratory scale in 1996. In this cell, the gel-polymer electrolyte was pressed between lithium foil on the one side and an air electrode on the other. (Later, usual liquid electrolyte in a porous, for example, glass fabric, separator was often used in lithium-air batteries). The whole cell was sealed into a plastic container ( coffee bag ) and small holes were made in the container wall adjacent to the air electrode to supply air under discharge and remove oxygen under charging. The air electrode was made of a mixture of particles of polymer electrolyte and carbon black with the catalyst supported on its surface (cobalt phthalocyanine). 

A porous electrode offers a far higher true working surface area and thus a much lower true current density (current per unit surface area of the electrode). Such an electrode consists of a metal or carbon-based screen or plate serving as the body or frame, current collector, and support for active layers, containing a highly dispersed catalyst for the electrode reaction. The pores of this layer are filled in part with the liquid electrolyte, and in part with the reactant gas. The reaction itself occurs at the walls of these pores along the three-phase boundaries between the solid catalyst, the gaseous reactant, and the liquid electrolyte. 

Lithium-air batteries [28] may also use a solid separator that will block dendrite growth from the anode to the cathode but allows permeation of the Li" ion between an anolyte and a catholyte. The simplest such separator would be a solid Li -ion solid electrolyte, but a porous glass containing the liquid electrolyte has been used where the anolyte and the catholyte are identical. As in the Zn-air primary battery, a porous carbon containing an oxygen-reduction catalyst on the pore walls and the liquid electrolyte in the pores provides the structure needed to facilitate the catalytic reaction of Li" ions with the gaseous O2 cathode. The cathodic reaction... 

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