Zeolites batteries, solid electrolytes

Zeolite-based solid electrolytes have been used in the manufacture of Li secondary batteries with the zeolite acting as the host for Li ions [174,176], These materials were applied as hosts for Zn11, in Zn-Mn02 batteries [177], and in Pb11 in lead acid batteries [178]. 

The last type of nickel based battery here considered is the so-called sodium-nickel chloride or Zebra battery, firstly developed in 80s in Pretoria, South Africa (Zebra stands for ZEolite Battery Research Africa). The anode is made of liquid sodium, the electrolyte is based on sodium ion conducting -alumina and the cathode is constituted by nickel chloride. This is flooded with liquid NaAlCU which acts as a secondary electrolyte, i.e., its function is to enhance the transport of sodium ions from the solid nickel chloride to and from the alumina electrolyte [19]. They work at high temperature (157°C is the temperature necessary to have sodium in its molten state, but the better performance is obtained in the range 250-350°C) and operate with the following discharge semi- reactions at the anode ... 

The predominant importance of the cations in zeolites is that they form so-called active sites for selective interaction with guest molecules in sorption and catalytic processes. From the point of view of advanced material science [47] they play a significant role in the formation of quantum-sized clusters with novel optical or semiconducting properties. As they give rise to cationic conductivity, zeolites can be used as solid electrolytes, membranes in ion-selective electrodes and as host structures in solid-state batteries. Organometallic compounds and coordination complexes can be readily formed on these cations within the larger cages or channels and applied to gas separation, electron-transport relays and hybrid as well as shape-selective catalysis [48]. 

Zeolites are essentially cationic conductors having temperature dependence of resistivity typically displayed by ionic conductors (higher mobility of ions at higher temperatures). By appropriate modifications of the zeolite composition, the conductivities of zeolites can be altered to allow their use as solid electrolytes, membranes in ion-selective electrodes, and as host stmctures for cathode materials in battery systems [84M1, 95A1]. 

ZEBRA battery is actually a Z E B R A (Zeolite Battery Research Africa) battery, that is, sodium-nickel chloride cell. This battery consists of a liquid Na negative electrode and NiCU separated by S-alumina solid electrolyte with Na" conduction. Total cell reaction is as follows ... 

A review is given of studies of reactions in ionic solid systems and of the implications of these studies for industrial applications. Work on the kinetics of solid-state reaction systems is discussed, as are studies of reaction mechanisms and of the effects of process variables on product characteristics. As examples of the significance of these studies for industry the formation of ferrites and of other spinels by reaction in the solid state, the use of catalytic processes employing such solid catalysts as zeolites, and the development of batteries and fuel cells using solid-state electrolytes are described. 

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