Liquid electrolyte systems

The PVdF—HFP separators used in PLION cells were around 3 mil thick, and had poor mechanical properties. It has been reported that the major source of rate limitation in PLION cells was the separator thickness. The rate capability of these cells can be significantly improved by decreasing the separator thickness to that typically used in liquid electrolyte system. Moreover, in the absence of shutdown function. the separator does not contribute to cell safety in any way. Park et al. reported that the HFP content in separators did not have any significant impact on cell performance. The Bellcore process has proven to be an elegant laboratory process but is difficult to implement in large-scale production. 

A unique approach in nonaqueous electrochemistry which may be applicable to several fields, especially for batteries, was recently presented by Koch et al. (private communication). They showed that it is possible to use solid matrices based on lithium salts contaminated with organic solvents as electrolyte systems. These systems demonstrate several advantages over liquid systems based on the same solvents and salts as solutions. Their electrochemical windows are larger, especially in the anodic direction (oxidation reactions), and it appears that their reactivity toward active electrodes (e.g., Li, Li—C) is much lower than that of the liquid electrolyte systems. 

The apparent safety advantage of a high flash point solvent which polymers can offer has motivated much study of liquid electrolyte systems which are di-... 

Thus, capacitative effects in electrode interface regions can be considerably different between solid and liquid electrolyte systems. However, EIS has been successfully applied to both solid and liquid electrolyte systems. 

It has long been known that liquid electrolyte systems that melted in the low hundreds of degrees were available in systems of metal chlorides and AICI3, and that some tetraalkylammonium salts melted at < 373 K. Hurley and Wier in 1951 showed that a 2 1 mixture of some complex organic chlorides with AICI3 gave liquid electrolytes at room temperatures. The discovery remained undeveloped for more than 25... 

In one of the low-melting liquid electrolyte systems containing AICI3 one has a changing acid/base character, depending on the ratio of AICI3 to the organic partner. 

In solid-state systems charge transport within the electrolyte is expected to be rate limiting. Even in liquid electrolyte systems there is some evidence for an influence of electrolyte on electron transport. This is expected from the screening and reorganization energy. In solid-state systems the absence of macroscopic fields cannot be assumed and drift may be expected to become significant. 

Fig. II.1.26 (a) Cyclic voltammogram [123] obtained in aqueous (0.1 M NaC104) media at 20°C for solid rran -[Cr(CO)2(dpe)2l mechanically attached to a polished basal plane pyrolytic graphite electrode (scan rate = 50 mV s ). (b) Schematic representation of redox processes at the interface between solid, electrode surface, and liquid electrolyte system...

When performing a run in practice, the remixing of separated zones, due to undesired convection and other movements in the liquid electrolyte system, has to be prevented. The liquid system must be stabilized against convection in some way. In electrophoresis such stabilization can be achieved in many ways. Valmet (53) has made the following summary on methods used ... 

Indeed, one matter of concern in the development of new polymer ionic membranes lies in the fact that their high conductivity is often associated with amorphous, low-viscosity phases. Therefore, in their conductive form, these membranes behave like soft solids with poor mechanical stability their direct use in LPBs may give rise to those problems commonly met in conventional liquid electrolyte systems, such as leakage, loss of interfacial contacts and short circuits. Under these circumstances, one of the most useful feature of LPBs, namely the solid-state configuration, would then be lost. Consequently, it is of key importance to assure that the polymer electrolyte membrane maintains good mechanical properties even in its conductive state. 

Recently, a series of IL electrolytes were tested for their applications in Li-S cells. Traditionally, the TFSI anion dominates the anion part of the ILs for the Li-S electrolytes, while typical cation examples are including the l-butyl-3- methyl-imidazolium (BMIM), l-ethyl-3-methylimidazolium (EMIM), 1-butyl-1-methy Ipyrrolidinium (PYR14), and 1-butyl-1-methylpiperidinium (PiP14) in Fig. 11 [18]. As in the traditional liquid electrolyte systems, the physical properties determine the solubility power charge distribution, polarity, viscosity and so forth. In the IL systems, however, the permittivity is largely independent of the combination of cations and anions, while variation in cations and anions affects the molecular level interactions, type/strengtii, and solvation. Due to unique properties, the ILs were studied as effective liquid electrolytes for the Li-S cells. 

Fig. 9.6 Examples of possible three-electrode cell geometries with embedded RE located at the counter side of solid electrolyte close to the WE [8, 26, 35], essentially similar to the use of a Luggin capillary probe in liquid-electrolyte systems. For (b), the cell dimensions according to [8] are given. The advantages and disadvantages of specific configurations shown in (a), (b) and (c) are discussed in the text...

Solid ceramic electrolyte used does not suffer electrolyte vaporization loss or excessive corrosion seen in high-temperature liquid electrolyte systems. 

Electrolyte System The AFC can be categorized into two main configurations, static electrolyte and mobile electrolyte systems. A schematic of the mobile electrolyte system is shown in Figure 7.25. In this system, the electrolyte is pumped from the stack into an electrolyte reservoir. The mobile electrolyte is constrained within the porous electrode structure either by asbestos or other porous separation layer between the electrode and the mobile electrolyte or by careful control of the differential pressure in the anode and cathode and the surface tension in the porous electrode structure as in the MCFC and PAFC liquid electrolyte systems. The use of a mobile electrolyte offers the following major advantages ... 

Sugimoto T, Atsumi Y, Kikuta M, Ishiko E, Kono M, Ishikawa M (2009) Ionic liquid electrolyte systems based on bis (fluorosulfonyl) imide for lithium-ion batteries. J Power Sources 189 802-805... 

Lin and co-workers ° prepared a nanocomposite of poly(n-isopropylacryl-amide) with MMT clay and applied it to a liquid electrolyte system as gel-lator. The DSSC assembled with the polymer nanocomposite electrolyte presented J c = 12.6 mA cm , Voc = 0.73 V, FF = 0.59 and rj = 5.4% while the DSSC prepared with the electrolyte gelled with the pure polymer... 

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