Positive plate performance

What is the influence of soaking on positive plate performance due to ... 

FIGURE 23.40 Performance curves of lead-acid stationary batteries at 25°C (S-shaped curves, based on positive-plate performance), (a) Antimony flat-pasted plate, 125 Ah at 8-h rate 290-mm height, 239-mm width, 8.6-mm thickness. Courtesy of Enersys, Inc.)... 

Demand for high performance SLI batteries has led to the development of smaller, lighter batteries that require less maintenance. The level of antimony is being decreased from the conventional 3—5% to 1.75—2.75% to minimise the detrimental effects. Lead alloys that contain no antimony have also been introduced. Hybrid batteries use a low antimony—lead alloy in the positive plate and a calcium—lead alloy in the negative plate. 

Glass fibres coated with Sn02 have been developed and used in lead-acid battery positive plates with the aim to improve the process of plate formation and the performance of the plate. 

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). 

POSITIVE-PLATE ADDITIVES TO ENHANCE FORMATION AND BATTERY PERFORMANCE... 

Table 4.1. Effect of glass microspheres on performance of positive plates [1].

Table 4.2. Effect of additives on performance of positive plates in terms of Ah per kg active material [7].

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. 

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. 

The delivery of too much overcharge can also result in damage to the positive active-material [24]. It has been suggested that the vigorous evolution and movement of gas as a result of this process can disrupt the internal structure of the active material. The related decrease in performance has been explained in terms of a loss of electrical conductivity within the positive plate due to progressive expansion of the active mass. 

This effect of antimony sustains the use of Ph—(5—10) wt% Sb alloys for casting grids and spines for the positive plates of traction batteries intended for deep discharge cycling duties. The performance characteristics of such batteries are more stable despite the higher water loss and hence the need for maintenance. 

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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