Superionic Conductors via Bulk Interfacial Conduction

Abstract

Superionic conductors with ionic conductivity on the order of mS cm-1 are expected to revolutionize the development of solid-state batteries (SSBs). However, currently available superionic conductors are limited to only a few structural families such as garnet oxides and sulfide-based glass/ceramic. Interfaces in composite systems such as alumina in lithium iodide have long been identified as a viable ionic conduction channel but practical superionic conductors employing the interfacial conduction mechanism are yet to be realized. Here we report a novel method that creates continuous interfaces in the bulk of composite thin films. Ions can conduct through the interface and consequently the inorganic phase can be ionically insu-lating in this type of bulk interface superionic conductors (BISCs). Ionic conductivities of lithium, sodium, and magnesium ion BISCs have reached 1.16 mS cm-1, 0.40 mS cm-1, and 0.23 mS cm-1 at 25 oC in 25 μm thick films, corresponding to areal conductance as high as 464 mS cm-2, 160 mS cm-2 and 92 mS cm-2, respectively. Ultralow over-potential and stable long-term cycling for up to 5000 hours was obtained for solid-state Li metal symmetric batteries employing Li ion BISCs. This work opens new structural space for superionic conductors and urges for future investigations on detailed conduction mech-anisms and material design principles.