| Summary: | Solid-state batteries with inorganic solid electrolytes are expected to be an efficient solutionto the issues of current lithium-ion batteries that are originated from their organic-solventelectrolytes. Although solid-state batteries had been suffering from low rate capability due tolow ionic conductivities of solid electrolytes, some sulfide solid electrolytes exhibiting high ionicconductivity of the order of 10−2 S cm−1 have been recently developed. Since the conductivity iscomparable to or even higher than that of liquid electrolytes, when taking the transport number ofunity into account, ion transport in solid electrolytes has ceased from rate-determining; however,it has been replaced by that across interfaces. The sulfide electrolytes show high interfacialresistance to the high-voltage cathodes. Our previous studies have demonstrated that oxidesolid electrolytes interposed at the interface reduces the resistance, and they also suggestthat the high resistance is attributable to a lithium-depleted layer formed at the interface. Thisstudy employs the first-principles calculation in order to gain insight into the interface. Theinterface structure between an oxide cathode/sulfide electrolyte simulated by the first-principlesmolecular dynamics has disclosed the presence of lithium-depleted layer at the interface, andthe electronic structure calculated on the basis of density functional theory strongly suggeststhat the charge current preferentially removes lithium ions from the sulfide electrolyte side ofthe interface to deplete the lithium ion there. These calculation results are consistent with thetransport mechanism proposed from the experimental results.
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