Batteries processes after formation

Processes After Formation of the Plates and During Battery Storage 537... 

Batteries intended to be used within 2 or 3 months after manufacture are produced with lead—ealeium—tin alloys, filled with electrolyte and ready for use. In this case, the technological scheme in Fig. 2.52 is modified. The tank formation and plate drying steps are eliminated and plate curing is followed by battery assembly, the formation process being completed in the battery itself. 

Two-shot formation process. The plates are formed in eells in a battery filled with H2SO4 solution of 1.15—1.10 relative density which serves as the formation electrolyte. After formation, the battery is set to a high current test discharge for 20 s, then it is recharged and the electrolyte is replaced with more concentrated solution of 1.30—1.32 relative density. This highly concentrated solution is diluted by the residual formation electrolyte in the plates and separators, and thus the required final electrolyte concentration of 1.28 relative density is reached. 

The more usual method of formation is to completely assemble the battery, fill it with electrolyte, and then apply the formation charge. This method is used for SLI and most stationary and traction batteries. A variety of formation conditions are used, similar to those for tank formation. The two major formation processes are the two-shot formation process (used for stationary and traction batteries) and the one-shot formation process (used for most SLI batteries). In the two-shot formation, the electrolyte is dumped to remove the low-density initial electrolyte and refilled with more concentrated electrolyte, chosen so that when this is mixed with the dilute initial acid residue which is absorbed in the elements or trapped in the case, the cell electrolyte will equilibrate at the desired density (Table 23.11). Typical values of the electrolyte specific gravity at full charge after formation are given in Table 23.12. 

The striking example is the reactivity of lithium with IE-VI layered compounds such as the decomposition of Li intercalated InSe with the formation of lithium selenide, Li2Se, observed by Raman spectroscopy on specimens prepared by various intercalation methods. The insertion of Li into M0S2 appears more stable with the occurrence of a superlattice formation at x(Li) 0.25 but a structural transformation from 2H-M0S2 (P-phase) to IT-M0S2 (a-phase) occurs for x l. This process is irreversible but the intercalation-deintercalation reaction is possible with the IT-M0S2, which could act as a positive electrode in rechargeable lithium batteries after formation of the cells. 

Particle size distributions of smaller particles have been made using electrical mobility analyzers and diffusion batteries, (9-11) instruments which are not suited to chemical characterization of the aerosol. Nonetheless, these data have made major contributions to our understanding of particle formation mechanisms (1, 1 ). At least two distinct mechanisms make major contributions to the aerosols produced by pulverized coal combustors. The vast majority of the aerosol mass consists of the ash residue which is left after the coal is burned. At the high temperatures in these furnaces, the ash melts and coalesces to form large spherical particles. Their mean diameter is typically in the range 10-20 pm. The smallest particles produced by this process are expected to be the size of the mineral inclusions in the parent coal. Thus, we expect few residual ash particles smaller than a few tenths of a micrometer in diameter (12). 

At the same time, it was found that Li metal is an unsafe negative electrode material [11, 13]. Upon charging a battery, lithium is electrodeposited on the Li metal electrode. During this process, formation of dendrites was observed, and after multiple charge/discharge cycles, those dendrites penetrated the separator and led to an internal short circuit of the cell with intense heat formation and sometimes even combustion of the cell. 

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