Formation of positive plates

The electrochemical reactions that proceed during the formation of positive plates can be represented by the following equations. Eh represents the equilibrium potential for the reaction at 298.15 K. 

Zonal processes are slow processes. They are responsible for the long duration of plate formation. Hence, it is important to find methods to by-pass the zonal processes. In order to accelerate the formation of positive plates, some conductive additives have been added to the positive pastes [28]. These additives increase the conductivity of the cured paste and formation proceeds almost uniformly throughout the whole plate volume as the electric current flows along the conductive additive network. The additives should be chemically stable in H2SO4 solution. Data have been reported about successful attempts to reduce the duration of the formation procedure to 8 h. 

The processes that occur during each of these stages should be taken into account when establishing the current (voltage) algorithm for formation of positive plates. The specific current and voltage values for the different formation stages are discussed below in Section 3.5.3. 

General current (voltage) algorithm for formation of positive plates... 

Three basic types of additives that shorten the time for formation of positive plates are currently used in the battery manufacturing practice. The effect of these additives can be summarised as follows ... 

Zonal processes are slow processes. They are responsible for the long duration of plate formation. Hence, it is important to find methods to by-pass the zonal processes. In order to accelerate the formation of positive plates, some conductive additives have been added to the... 

Mechanisms of the Crystallization Processes During Formation of Positive Plates with 4BS Paste... 

The final step of positive plate fabrication is the formation process. This process converts all of the positive paste into p-Pb02 active mass. Normally, the formation of positive plates can be divided into two stages [15] ... 

In practice, to enhance the formation of positive plates, some conductive agents are needed as additives to the positive pastes. These additives can increase the conductivity of the cured paste and also benefit the uniform current distribution throughout the entire Pb02 layer. Note that these additive compounds should be chemically stable in strong H2SO4 solution. The additive materials are normally (1) carbon, (2) conductive polymers (polyaniline, polypyrrole polyparaphenylene and polyacetylene in the form of powers or fibers), (3) doped Sn02, and (4) lead or red lead. 

C and 3BS crystals are converted into 4BS crystals of irregular shape (Fig. 3.38), with good connection between themselves and with the current-collector. Formation of such pastes takes more than 48 h. This technology is used for the production of all types of positive plates. If the time of steam treatment is extended to 8-10 h and the temperature of the plate is higher than 90°C, the resulting 4BS crystals are very thick and the formation of such pastes requires several days. When this method is applied to the manufacture of positive plates for stationary batteries, service lives of over 15 years are achieved. 

Selection of a particular method for the production of 4BS pastes depends on the type of battery application, the time of plate formation and the planned service life of the battery. 4BS pastes are gaining an ever-increasing share in the production of positive plates for lead-acid batteries. 

It has been established that on cycling of tubular positive plates with die-cut strap grids (SGTP) or of positive plates with expanded grids with flat ribs, a rapid capacity loss is observed (the PCL-1 effect, see Section 2.3, Chapter 2 and Chapter 9) [54]. The reason for this capacity loss is the formation of groups of PbS04 crystals in the layer of the PAM that contacts the current-collector (Fig. 3.39). These PbS04... 

Fig. 3.58. Schematic of cross-section through structure of positive plate during formation.

The basic components of the paste are crystal phases of 3BS or 4BS, small amounts of orthorhomb-PbO, tet-PbO and Pb. These are detected by X-ray diffraction methods. If a paste is prepared from crystal phases of 3BS and tet-PbO in the same proportion as in the paste prepared from leady oxide and H2SO4, and then grids are pasted with this paste and set to curing and formation, the obtained PAM is mechanically unstable and difficult to form, and hence the plates have low capacity. Valeriote has found that one of the reasons for the low energetic characteristics of positive plates is the lack of amorphous components in the paste [17]. The content of amorphous phases should amount to 15—10%. Such amorphous components in the paste are most often hydroxides. Some of the amorphous hydroxides are obtained as a result of oxidation of Pb in the leady oxide during paste preparation and plate curing. And the content... 

The influenee of time on soaking of positive plates prior to formation on the initial battery eapaeity has been studied [13]. Batteries are formed with a quantity of eleetricity corresponding to 250% of their theoretical capacity. The results of the first discharge at 20 h rate are presented in Fig. 9.34. 

Formation of Positive Lead—Acid Battery Plates 445... 

---