The processes that occur at single crystals of an active substance embedded in an electroconducting porous matrix are considered. Conversion of solid reagents is assumed to proceed via a liquid-phase scheme as follows: dissolution–electrochemical reaction–crystallization. A set of equations is proposed. The set having been solved, an analytical expression is derived for a local polarization characteristic as a function of polarization, oxidation state of reagents, and structural and physicochemical parameters of the system. In order to check the model, galvanostatic characteristics of the electrodes made of the mixture of chloranile (C
) and carbon black have been investigated. The theoretical and experimental characteristics show very good agreements.