Liquid electrolyte

In the first papers dealing with SEI electrodes it was suggested that the passivating layer consists of one or two layers [1, 2], The first one (the SEI) is thin and compact the second (if it exists), on top of the SEI, is a more porous, or structurally open, layer that suppresses the mass transport of ions in the electrolyte filling the pores of this layer. 

According to this model, the SEI is made of ordered or disordered crystals that are thermodynamically stable with respect to lithium. The grain boundaries (parallel to the current lines) of these crystals make a significant contribution to the conduction of ions in the SEI [1, 2], It was suggested that the equivalent circuit for the SEI consists of three parallel RC circuits in series combination (Fig. 12). Later, Thevenin and Muller [29] suggested several modifications to the SEI model  

The first two models are irrelevant to lithium-battery systems since the PEIs are not thermodynamically stable with respect to lithium. Perchlorate (and other anions but not halides) were found to be reduced to LiCl [15, 16, 22-27]. It is commonly accepted that in lithium batteries the anode is covered by SEI which consists of thermodynamically stable anions (such as 02, S2-, halides). Recently, Aurbach and Za-ban [25] suggested an SEI which consists of five different consecutive layers. They represented this model by a series of five 

It is well known today that the SEI on both lithium and carbonaceous electrodes consists of many different materials including LiF, Li2C03, LiC02R, Li20, lithium alkoxides, nonconductive polymers, and more. These materials form simultaneously and precipitate on the electrode as a mosaic of microphases [5, 6], These phases may, under certain conditions, form separate layers, but in general it is more appropriate to treat them as het-eropolymicrophases. We believe that Fig. 13(a) is the most accurate representation of the SEI. 

The equivalent circuit of a section of this SEI is presented in Fig. 13(b). It was recently found [123, 124] that at temperatures lower than 90 °C, the grain-boundary resistance of composite polymer electrolytes and composite solid electrolytes based on Lil-A Ojis many times larger than their ionic resistance. At 30 °C / GB is several orders of magnitude larger than (the ionic resistance) and for 100 pm-thick CPE foils or Lil-A Oj pellets it reaches [125] 105-106Qcm2 (depending on CPE composition). 

According to this model, the SEI is made of ordered or disordered crystals that are thermodynamically stable with respect to lithium. The grain boundaries 

1) the polymer electrolyte interphase (PEI) model, in which the lithium in PC electrolyte is covered with a PET which consists of a mixture of Li2C03, P(PO) x, and IiCl04, where P(PO), is polypropylene oxide, formed by reduction-induced polymerization of PC  

2) the soUd-polymer-layer (SPL) model, where the surface layer is assumed to consist of solid compounds dispersed in the PE  

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Through static electrodes liquid electrolyte or chemical resistance starting... 

Figure 4.9 Smooth acceleration through liquid electrolyte starters...

Figure 4.10 A typical liquid electrolyte electrode assembly (Courtesy AOYP Engineering)...

Molten halides are liquid electrolytes in many instances, and their decomposition may be canned out in principle to produce the metal and halogen, usually in the gaseous state. The theoretical decomposition voltage, E°, is calculated from the Gibbs energy of formation tlrrough the equation... 

A number of attempts to produce tire refractory metals, such as titanium and zirconium, by molten chloride electrolysis have not met widr success with two exceptions. The electrolysis of caesium salts such as Cs2ZrCl6 and CsTaCle, and of the fluorides Na2ZrF6 and NaTaFg have produced satisfactoty products on the laboratory scale (Flengas and Pint, 1969) but other systems have produced merely metallic dusts aird dendritic deposits. These observations suggest tlrat, as in tire case of metal deposition from aqueous electrolytes, e.g. Ag from Ag(CN)/ instead of from AgNOj, tire formation of stable metal complexes in tire liquid electrolyte is the key to success. 

Carbon nanotubes mixed with ruthenium oxide powder, and immersed in a liquid electrolyte, have been shown by a Chinese research group to function as supercapacilors with much larger capacitance per unit volume than is normally accessible (Ma et al. 2000). 

Conventional batteries consist of a liquid electrolyte separating two solid electrodes. In the Na/S battery this is inverted a solid electrolyte separates two liquid electrodes a ceramic tube made from the solid electrolyte sodium /5-alumina (p. 249) separates an inner pool of molten. sodium (mp 98°) from an outer bath of molten sulfur (mp 119°) and allows Na" " ions to pass through. The whole system is sealed and is encased in a stainless steel canister which also serves as the sulfur-electrode current collector. Within the battery, the current is passed by Na+ ions which pass through the solid electrolyte and react with the sulfur. The cell reaction can be written formally as... 

Interest in using ionic liquid (IL) media as alternatives to traditional organic solvents in synthesis [1 ], in liquid/liquid separations from aqueous solutions [5-9], and as liquid electrolytes for electrochemical processes, including electrosynthesis, primarily focus on the unique combination of properties exhibited by ILs that differentiate them from molecular solvents. 

The aim of this chapter is to give a state-of-the-art report on the plastic solar cells based on conjugated polymers. Results from other organic solar cells like pristine fullerene cells [7, 8], dye-sensitized liquid electrolyte [9], or solid state polymer electrolyte cells [10], pure dye cells [11, 12], or small molecule cells [13], mostly based on heterojunctions between phthaocyanines and perylenes [14], will not be discussed. Extensive literature exists on the fabrication of solar cells based on small molecular dyes with donor-acceptor systems (see for example [2, 3] and references therein). 

Table 13. Separators for valve-regulated lead -acid batteries (liquid electrolyte)...

Batteries with gelled electrolyte have been shown to require a separator in the conventional sense, to secure spacing of the electrodes as well as to prevent any electronic shorts the latter is achieved by microporous separators. An additional important criterion is minimal acid displacement, since these batteries — in comparison with batteries with liquid electrolyte — lack the electrolyte volume share taken up by gelling and by the cracks. 

It was also shown in 1983 [11] that lithium can be reversibly inserted into graphite at room temperatures when a polymeric electrolyte is used. Prior experiments with liquid electrolytes were unsuccessful due to co-intercalation of species from the organic electrolytes that were used at that time. This problem has been subsequently solved by the use of other electrolytes. 

Film-forming chemical reactions and the chemical composition of the film formed on lithium in nonaqueous aprotic liquid electrolytes are reviewed by Dominey [7], SEI formation on carbon and graphite anodes in liquid electrolytes has been reviewed by Dahn et al. [8], In addition to the evolution of new systems, new techniques have recently been adapted to the study of the electrode surface and the chemical and physical properties of the SEI. The most important of these are X-ray photoelectron spectroscopy (XPS), SEM, X-ray diffraction (XRD), Raman spectroscopy, scanning tunneling microscopy (STM), energy-dispersive X-ray spectroscopy (EDS), FTIR, NMR, EPR, calorimetry, DSC, TGA, use of quartz-crystal microbalance (QCMB) and atomic force microscopy (AFM). 

It is not clear why <2IR is twice as large [6, 76, 96] (or more) in polymer electrolytes than it is in liquid electrolytes. This may result from larger <2SP and larger <2SE] due to partial exfoliation. 

The major differences between polymer and liquid electrolytes result from the physical stiffness of the PE. PEs are either hard-to-soft solids, or a combination of solid and molten in phases equilibrium. As a result, wetting and contact problems are to be expected at the Li/PE interface. In addition, the replacement of the native oxide layer covering the lithium, under the... 

Of course these requirements cannot be fulfilled simultaneously. For example, a low vapor pressure of the liquid electrolyte is obtained only by using more viscous dipolar aprotic solvents such as propylene carbonate, but high solvent viscosity generally entails a low conductivity. Nevertheless, a large number of useful solvents and electrolytes is available, allowing a sufficiently good approximation to an ideal electrolyte. 

TablelO. Conductivities of various lithium ion containing liquid electrolytes...

The conductivity of gelled electrolytes is determined primarily by the liquid and salt components. High liquid content, of the order of 40 percent, is required to attain conductivities comparable with those of the corresponding liquid electrolyte. At these liquid loading levels there is often insufficient mechanical strength, and although this effect may not be noticeable on 1-2 cm2 laboratory cells, it is certainly evident on scale-up [111]. Polymer blends such as PEO-MEEP are much more mechanically stable than MEEP itself and more conductive than PEO but there is little overall improvement of the room tern-... 

The preparation and properties of a novel, commercially viable Li-ion battery based on a gel electrolyte has recently been disclosed by Bellcore (USA) [124]. The technology has, to date, been licensed to six companies and full commercial production is imminent. The polymer membrane is a copolymer based on PVdF copolymerized with hexafluoropropylene (HFP). HFP helps to decrease the crystallinity of the PVdF component, enhancing its ability to absorb liquid. Optimizing the liquid absorption ability, mechanical strength, and processability requires optimized amorphous/crystalline-phase distribution. The PVdF-HFP membrane can absorb plasticizer up to 200 percent of its original volume, especially when a pore former (fumed silica) is added. The liquid electrolyte is typically a solution of LiPF6 in 2 1 ethylene carbonate dimethyl car-... 

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