Gelled electrolyte

Separator s a physical barrier between the positive and negative electrodes incorporated into most cell designs to prevent electrical shorting. The separator can be a gelled electrolyte or a microporous plastic film or other porous inert material filled with electrolyte. Separators must be permeable to ions and inert in the battery environment. 

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. 

Table 14 compares the most important physicochemical data of separators used in batteries with gelled electrolyte. 

Table 14. Separators for valve-regulated lead-acid batteries (gelled electrolyte)...

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 liquid electrolytes used in lithium batteries can be gelled by addition of a polymer [25] or fumed silica [26], or by cross linking of a dissolved monomer [271. Depending on the mechanical properties, gelled electrolytes can be used as separators, or supported by a conventional [27]... 

The electrolyte was a solution of ammonium chloride that bathed the electrodes. Like Plante s electrochemistry of the lead-acid battery, Leclanche s electrochemistry survives until now in the form of zinc-carbon dry cells and the use of gelled electrolyte.12 In their original wet form, the Leclanche electrochemistry was neither portable nor practicable to the extent that several modifications were needed to make it practicable. This was achieved by an innovation made by J. A. Thiebaut in 1881, who through encapsulating both zinc cathode and electrolyte in a sealed cup avoided the leakage of the liquid electrolyte. Modern plastics, however, have made Leclanche s chemistry not only usable but also invaluable in some applications. For example, Polaroid s Polar Pulse disposable batteries used in instant film packs use Leclanche chemistry, albeit in a plastic sandwich instead of soup bowls.1... 

Button cells consist of cathode and anode cans (used as the terminals), powdered zinc anode, containing gelled electrolyte and the corrosion inhibitor, separator with electrolyte, thin (0.5 mm) carbon cathode with catalyst and PTFE, waterproof gas-permeable (teflon) layer and air distribution layer for the even air assess over the cathode surface. Parameters of battery depend on the air transfer rate, which is determined by quantity and diameters of air access holes or porosity of the gas-diffusion membrane. Air-zinc batteries at low rate (J=0,002-0,01C at the idle drain and J= 0,02-0,04C at the peak continuous current) have flat discharge curves (typical curve is shown by Figure 1). 

A compromise is to add some gelled electrolyte. Commercial cells use a porous polyethylene or polypropylene separator filled with a polymer and gel filling with a liquid electrolyte. They offer improved safety with more resistant to overcharge and less chance for electrolyte leakage. 

Separators for batteries can be divided into different types, depending on their physical and chemical characteristics. They can be molded, woven, non-woven, microporous, bonded, papers, or laminates. In recent years, there has been a trend to develop solid and gelled electrolytes that combine the electrolyte and separator into a single component. 

Such thin KOH-treated gelatinized agar electrolyte was also applied between the electrode-gelled electrolyte interfaces [332]. 

In the gelled electrolyte battery, die sulfuric acid electrolyte has been immobilized by a diixolropic gel. This is made by mixing an inorganic powder such as silicon dioxide, SiCL, with the acid. Other cells use a highly absorbent separator to immobilize the electrolyte. 

Polymeric electrolytes, polymer-salt complexes, and gelled electrolytes, e.g., benzyl sulfonic acid siloxane, polyethylene oxide (imine, succinate)-LiC104, and PVDF gel in THF containing a mixture of Bu2Mg and AlEtCl2, respectively. 

When VRLA batteries are container-formed, filling of the cells with H2SO4 solution is a delicate process, especially when using gelled electrolyte. Since the plate group is under compression, the efficacy of the filling process depends on the following parameters. 

Tests were also performed using VRLA batteries with gelled electrolyte [9]. The additives gave benefits similar to those obtained with AGM batteries. It was concluded that the porosity additives could have a positive effect on battery capacity. Future work with these additives will continue and involve full-scale batteries. 

One of the most successful applications of phosphoric acid has been in gelled electrolytes that are made by adding fumed silica to sulfuric acid [73,74]. Larger phosphate concentrations appear to be tolerated in the gelled acid without adversely affecting cell performance. One reason may be that the plates in these batteries are formed by the dry-charge process and the phosphate is added to the battery with the electrolyte. Addition of silica may also affect the equilibria of phosphate dissociation and/or lead phosphate formation. Further study of these effects may lead to a better understanding of how to control phosphate activities to enhance battery performance. 

The battery was assembled from VRLA modules of a gelled-electrolyte design, which had excellent deep-discharge capabilities. The modules had lead-coated copper terminals and bus bars, a status indicator that warned if the SoC dropped below 20%, and an internal air manifold for thermal management. The facility contained 64 modules connected in series to produce a 384-V, 1500-Ah battery. 

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