Interplay Between Two Adjacent Electrical Double Layers at Metal | Solid Electrolyte | Liquid Electrolyte Interfaces

Electrical double layer (EDL) in modern batteries is radically different from that of the mercury electrode for which the conventional EDL models were initially developed. Particularly, the formation of a solid electrolyte interphase (SEI) divides the electrode–solution interface into two adjacent interfaces, while the interplay between these two EDLs is largely unclear. Herein, considering a metal | solid electrolyte | liquid electrolyte (M|SE|LE) system, we developed continuum models to understand the correlation between the charging states of the two adjacent EDLs. In addition to numerical results, analytical solutions of the differential double layer capacitances for two limiting cases, where the mobile charge countering the metal surface charge exists in either the SE or the LE, are obtained. The critical electrode potential marking the transition between the two limiting cases is analyzed. This work contributes to the understanding of nontraditional electrochemical interfaces in modern batteries.