The second major factor affecting the performance of Li/SOCl2 cells is the cathode freeze-over. This is the formation of LiCl products in the outer portion of the cathode to the extent that it blocks access to unused reaction sites.
As explain in the section of Chemistry of Li/SOCl2 Cells, the discharge of Li/SOCl2 cells results in the formation of LiCl in the cathode. If the cell is discharged at low rates ( < 2.0 mA/cm2 ), the LiCl is evenly distributed throughout the carbon cathode which results in the efficient use of the active sites available for the reduction of SOCl2.
At rates above 2.0 mA/cm2, the reduction of SOCl2 occurs predominately on the outer surfaces of the carbon cathode. The outer surface of the cathode effectively “freezes over” with LiCl (see Diagram 5), and the inner active surfaces become inaccessible. Unlike passivated anodes which can be recovered, cathodes that have been “frozen over” are irreparably damaged and capacity loss will result.
Diagram 5 shows a cross-sectional view of undischarged cathodes, high rate discharged cathodes ( >2 mA/cm2), and low rate discharged cathodes (<2 mA/cm2).
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