Current-Producing and Other Processes in Primary Power Sources

2 CURRENT-PRODUCING AND OTHER PROCESSES EM PRIMARY POWER SOURCES 

The current-producing anodic process in all cells is reduced to lithium dissolution with the formation of its ions  

The rate of this process in aprotic electrolytes is rather high the exchange current density is fractions to several mA/cm. As pointed out already, the first contact of metallic lithium with electrolyte results in practically the instantaneous formation of a passive film on its surface conventionally denoted as solid electrolyte interphase (SEI). The SEI concept was formulated yet in 1979 and this film still forms the subject of intensive research. The SEI composition and structure depend on the composition of electrolyte, prehistory of the lithium electrode (presence of a passive film formed on it even before contact with electrode), time of contact between lithium and electrolyte. On the whole, SEI consists of the products of reduction of the components of electrolyte. In lithium thionyl chloride cells, the major part of SEI consists of lithium chloride. In cells with organic electrolyte, SEI represents a heterogeneous (mosaic) composition of polymer and salt components lithium carbonates and alkyl carbonates. It is essential that SEI features conductivity by lithium ions, that is, it is solid electrolyte. The SEI thickness is several to tens of nanometers and its composition is often nonuniform a relatively thin compact primary film consisting of mineral material is directly adjacent to the lithium surface and a thicker loose secondary film containing organic components is turned to electrolyte. It is the ohmic resistance of SEI that often determines polarization of the lithium electrode. 

The cathodic process is determined by the nature of the active material. As arule, processes on positive electrodes are much more complicated than processes on lithium. 

Desolvated lithium ions are intercalated into the crystalline lattice under discharge of solid cathodes, including oxides and chalcogenides. The charge of lithium ions remains herewith unchanged and the atoms of the active substance metal are reduced. 

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