Positive plate cycle life

Nickel oxide electrodes constitute the positive plates of several storage systems (among which nickel-zinc, nickel cadmium, nickel metal-hydride, sodium-nickel chloride) [16]. In recent years, the high-specific energy and specific power of Ni-Zn systems has increased the interest in their use for electric vehicles with respect to the past years, when their application was essentially limited by a short cycle life. 

Influence of basic lead sulfates on cycle-life of positive plates... 

The dependencies of the phase composition of the paste and the cycle-life of the positive plates on the acid-to-oxide ratio used for paste preparation are presented in Fig. 3.33 [34]. The relative intensities of the characteristic diffraction lines for the different phases in pastes prepared using different acid-to-oxide ratios are shown in Fig. 3.33 (a) and (b). The sulfation of the pastes increases with increase in acid content. 

In positive-plate manufacture, 3BS and 4BS phases are never used alone. They are always in combination with PbO, which improves the connection between the basic lead sulfate crystals and hence facilitates the formation of a mechanically strong porous mass or skeleton. The ratio between the basic lead sulfates and the PbO in the pastes exerts an influence on the initial capacity and the cycle-life performance of the battery, namely the higher the PbO content in the paste, the lower is the initial capacity of the positive plates (Fig. 3.33). 

The conductive polymers were also tested at levels of 13 wt.% in a positive plate which contained PbS04, a-Pb02, and p-Pb02 [22]. The optimum concentration was found to be lwt.%. At 2 3 wt.% additive, the discharge capacity was increased by about 30% and the specific surface-area from 3-4 to 5-6m g. Cycle-life declined at additive concentrations above 5wt.% due to mechanical instability of the electrode. Polypyrrole and polythiophene oxidized during overcharge, but polyaniline remained stable. 

Both sets of studies show that additions of carbon to the positive electrode have the greatest benefit during formation. Although the carbon influences the plate morphology, it does not appear to have much effect on cell performance or cycle-life. This is probably because earbon is oxidized in the positive-plate environment to form gaseous earbon dioxide. 

The addition of sulfates to the positive plate was evaluated by Lorenz (as described in Ref. 58). Results showed that 0.5wt.% barium sulfate or strontium sulfate added to the positive active-material reduced the cycle-life from 100 cycles without the additive to 30-50 cycles with the additive under the same conditions. The end-of-life was taken as a 40% decline in the initial capacity. Lorenz further reported that calcium sulfate is not isomorphous with lead sulfate and therefore has no effect on battery life. (Note, calcium sulfate also does not act as an inorganic expander for negative plates.)... 

The cycle-life of cells discharged at the C/5 rate to 0.7 V was found to decrease when 0.3 or 3wt.% BaS04 was added to the positive plate [59]. Compared with an undoped plate, the addition of 3 wt.% BaS04 decreased the cycle-life by a factor of... 

Another feature of AGM separators is their compressibility. With compression of the plate and separator stack, this AGM property guarantees good plate-separator contact, even if the plates are not perfectly smooth. Also, battery assembly is facilitated since the stack can be easily inserted into the cell after compression to a thickness lower than the cell dimension. An undesirable result of the compressibility is that the AGM separator does not exert sufficient resistance against expansion of the positive plate during battery cycle-life. This expansion is particularly prevalent in deep-cycle applications and can cause the battery to suffer premature capacity loss (PCL) via reduced inter-particle conductivity — a phenomenon known as PCL-2 [7]. In the literature, two additional characteristics, which are related to the PCL-2 failure mode, are discussed, namely, AGM separators shrink when first wetted with electrolyte and their fibres can be crushed at high pressure levels [8-10]. These features result in a loss of separator resilience, i.e., a lessening of the ability to display a reversible spring effect. 

It is well recognized that the architecture of the VRLA cell predisposes it to long cycle-life. The common failure modes for flooded automotive batteries are grid corrosion, lack of water, and damage to the positive plate [4]. Of these failure modes, VRLA may show some reduction in the extent of damage to the positive plate by... 

Float operation with an occasional discharge is the standard service of standby batteries. In some cases, however, the application includes more discharges than usual, and this means that some cycling performance is also needed. The result of an 80% DoD cycle test with 6-V, 240-Ah gel batteries is shown in Fig. 13.5. Every 50 cycles there was a capacity test. It can be seen that there is a rather long time period where the capacity is rather stable around 100%. After about 600 cycles the capacity decreased steadily, reaching the 80% level after 800 cycles. This result is typical for gel batteries with flat positive plates. In general, gel batteries have a rather good cycle-life. 

Purpose-built batteries. Gel batteries with either tubular plates or thick, flat plates (> 5 mm) are recommended when a long cycle-life is required. Both designs have a high level of resistance to positive-plate degradation, and can tolerate high levels of positive-grid corrosion. 

Lower-cost batteries. For applications that do not require both a long cycle-life and a high level of reliability under extreme conditions, less expensive, standard fiat-plate, gel batteries can prove cost-effective. These batteries typically provide 800 cycles to 75% DoD, which is half that of the purpose-built designs. This reduction in cycle-life is primarily related to the use of less robust positive plates (typically 3-mm thick) and less attention to detail in the general construction of the... 

An aqueous solution of electrochemically oxidized graphite has been tested as an additive to the sulfuric acid electrolyte [47]. The carbon colloid addition improves the discharge capacity and extends the cycle life of the battery. This additive improves the electrical contact between Pb02 particles in the positive plates and thus increases the discharge capacity and the charge acceptance of the lead—acid battery. 

Tin improves the mechanical properties of Pb—Ca—Sn alloys. It reduces the passivation phenomena that proceed on the positive battery plates and improves the corrosion resistance of the positive grids. Tin increases also the creep resistance of the Pb—Ca—Sn alloys and thus sustains a good contact between the CL and the PAM. The combination of high corrosion resistance and high creep resistance of the grids prolongs the cycle life of the batteries. 

Cycle Life of Positive Plates as a Function of Phase Composition of the Paste [19]... 

It has been established experimentally that the phase composition of the paste exerts a stronger influence on the capacity and cycle life of positive plates than on negative ones. 

Biagetti and Weeks [14] have established that plates produced with 4BS pastes have almost twice longer cycle life than 3BS plates. Culpin [20] has investigated SLI batteries with 4BS positive plates and has found that their cycle life at 20 h discharge rate and their CCA performance (at —18 °C) are similar to those for SLI batteries with positive plates prepared with 3BS pastes. However, 4BS batteries have longer cycle life (by 50%) than that of 3BS batteries at 1 h and 5 h discharge rates. 

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