Characteristics of an ideal all solid-state battery

In an ideal solid-state battery involving protonic reactions, the solid electrolyte must be only a protonic conductor the proton transference number should be equal to unity (t(H+ = 1). Then all the previous reactions cannot occur and it is theoretically possible to use electrode materials which were unstable in the presence of a liquid aqueous electrolyte. 

For example, the positive electrode material y-Mn02 can be associated with a solid protonic conductor containing H at a high concentration and can then be used to give the benefit of its high acidic potential. If t(H+) is equal to unity in the electrolyte, and if the negative electrode delivers protons into this electrolyte when anodically polarized, the only cathodic reaction will be the insertion of protons into Mn02, and the formation of Mn is not possible. 

Another interesting case is given by Pb02 into which protons cannot be cathodically inserted in the presence of sulphuric acid because of the lead sulphate interfacial precipitation. This insertion is possible with a solid protonic conductor (SPC) as electrolyte. 

Let us consider an ideal battery of this type. Fig. 37.1. During dischaige, the negative electrode must supply protons to the solid electrolyte in which they are carried to the other electrode by a translocation/vehicular mechanism. Then they must penetrate into the positive electrode material. 

Both electrodes must present a mixed conductivity - electronic and protonic - with an internal RedOx couple giving a potential high enough (versus a hydrogen electrode) for the positive electrode and sufficiently low for the negative one. 

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