Stable zero-sodium-excess solid-state batteries enabled by interphase stratification

Zero-sodium-excess solid-state batteries (ZSBs) are promising to overcome the disadvantage of low energy density for Na-ion batteries, but the interfacial issues between the solid-state electrolytes and current collectors remain bottlenecks for their practical applications. Herein, we report a self-regulated stratification of the artificial interphase through the conversion reaction between MgF 2 modification layer and Na metal. Ascribed to the huge adsorption energy difference between Al–Mg and Al–NaF, the sodiophilic Mg concentrated at the bottom side and served as the nucleophilic seed for Na, while sodiophobic NaF on the top side provided high thermodynamic stability for Na dendrite and side reaction suppressions. Consequently, the as constructed ZSBs with Na 3 V 2 (PO 4 ) 3 cathode exhibited prominent energy density of 254.4 ​Wh kg −1 (calculated based on the total mass of electrode and electrolyte) with a capacity retention of 82.7% over 350 cycles. This work paves a feasible way to achieve high performance and stable ZSBs. The stratification of the interphase was realized by the conversion reaction between MgF 2 modification layer and Na metal, as well as the huge adsorption energy difference between Al–Mg and Al–NaF. The sodiophilic Mg at the bottom side served as the Na nucleophilic seed, while sodiophobic NaF on the top side provided high thermodynamic stability for Na dendrite and side reaction suppressions, which significantly improved the electrochemical performance of the ZSBs. • A feasible interphase design through a novel stratification strategy is proposed. • The adsorption energy difference between Al/Mg and Al/NaF leads to stratification. • The as constructed ZSB displays a high energy density of 254.4 ​Wh/kg.