Positive active mass volume

With the introduction of lead—calcium alloys for the plate grids, however, the life of the battery on deep discharge cycling declined dramatically to 20—25 cycles. This phenomenon was first called Sb-free effect and later premature capacity loss (PCL effect) [20]. It was established that the PCL effect was a result of certain processes that proceed at the positive battery plate, more precisely at the interface grid/positive active mass (PCL-1 effect) [21] and/or in the positive active mass volume (PCL-2 effect) [22]. 

Therefore, passivation of the positive electrode by poorly conducting PbS04 can be reduced [348]. The porosity is important because it enables the expansion during the solid phase volume increase, which accompanies the transformation of Pb02 to PbS04. In the most popular construction, the electrode paste material (mixture of metallic lead with lead oxides) is held in a framework composed of lead alloys with additions of tin, antimony, selenium, and calcium [348]. Antimony improves the mechanical stability however, it increases the resistance and facilitates the selfdischarge of the battery. Better results are obtained for low antimony content and/or for lead-calcium alloys [203]. Methods of positive electrodes improvement, from the point of view of lead oxide technology have been discussed [350]. Influence of different factors on life cycle, nature, and composition of the positive active mass has been studied by Pavlov with coworkers [200, 351, 352]. 

Positive plates need much more time to form than negatives. The reason for this is the dielectric behaviour of the cured positive paste. Oxidation of the bivalent lead compounds in the paste and formation of the Pb02 positive active mass passes through a number of chemical reactions, some of which proceed at a low rate, which retards the technological process of formation of the positive plate. In an attempt to accelerate the formation process, additives to the positive paste have been looked for, which are characterised by electro-conductive properties and stability in sulfuric acid. These additives create an electro-conductive network in the paste and the process of oxidation proceeds simultaneously within a large paste volume, thus accelerating plate formation. 

Eor the negative electrolyte, cadmium nitrate solution (density 1.8 g/mL) is used in the procedure described above. Because a small (3 —4 g/L) amount of free nitric acid is desirable in the impregnation solution, the addition of a corrosion inhibitor prevents excessive contamination of the solution with nickel from the sintered mass (see Corrosion and corrosion inhibitorsCorrosion and corrosion control). In most appHcations for sintered nickel electrodes the optimum positive electrode performance is achieved when one-third to one-half of the pore volume is filled with active material. The negative electrode optimum has one-half of its pore volume filled with active material. 

When scaling a conventional centimetre-sized reactor down to the micron scale, the surface-to-volume ratio significantly increases to the point where the container walls can effectively become an active or influential part of the reaction or process occurring in the fluidic channel. Clearly this attribute of micro-reactors can be viewed in a positive way and leads to the opportunity of exploiting surface-dependent performance including electrokinetic driven flow, surface functionalisation and mass transfer, and heat transfer. 

To transform Equation 6.3 into a more useful form, we need to incorporate expressions for the chemical potentials of the species involved. The chemical potential of species j was presented in Chapter 2 (Section 2.2B), where Xj is a linear combination of various terms fij = fi + RT In cij +VjP -f ZjFE 4- mjgh (Eq. 2.4 fi is a constant, cij is the activity of species /, Vj is its partial molal volume, P is the pressure in excess of atmospheric, Zj is its charge number, Fis Faraday s constant, E is the electrical potential, m is its mass per mole, and h is the vertical position in the gravitational field). 

When VRLABs were adopted for mass production, the volume of H2SO4 electrolyte in the battery was confined to the amount that the AGM separator could absorb. In order to preserve the quantity of H2SO4 as active material, its density was increased to 1.31 g cm and even to 1.34 g cm . This led to a dramatic drop in capacity of the positive plates. 

One of the battery prototypes for electric vehicles had a volume of 3201 and mass of 820 kg. The positive electrode is manufactured from FeS with the addition of C0S2. A few layers of the active material alternating with graphitized fabric are placed into a basket of molybdenum mesh welded to the central molybdenum current collector. The positive electrode is wrapped into a two-layer separator. The inner layer consists of Zr02 fabric and the outer layer of BN fabric. The negative electrode consists of a lithium-silicon alloy in the porous nickel matrix. The container and the cover are manufactured from stainless steel and electrically connected to the negative electrode. The prototype was drained with current up to 50 A, and the specific power was as high as 53 W/kg (Martino FJ et al, 1978). 

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