Developing argyrodite-type, chlorine-rich, sodium-ion, solid-state electrolytes with high conductivity is a long-term challenge that is crucial for the advancement of all-solid-state batteries (ASSBs). In this study, chlorine-rich, argyrodite-type Na_6−xPS_5−xCl_1+x solid solutions were successfully developed with a solid solution formation range of 0 ≤ x ≤ 0.5. Na_5.5PS_4.5Cl_1.5 (x = 0.5), displaying a highest ionic conductivity of 1.2 × 10⁻³ S/cm at 25 °C, which is more than a hundred times higher than that of Na₆PS₅Cl. Cyclic voltammetry and electrochemical impedance spectroscopy results demonstrated that the rich chlorine significantly enhanced the ionic conductivity and electrochemical stability, in addition to causing a reduction in activation energy. The Na_5.5PS_4.5Cl_1.5 composite also showed the characteristics of a pure ionic conductor without electronic conductivity. Finally, the viability of Na_5.5PS_4.5Cl_1.5 as a sodium electrolyte for all-solid-state sodium batteries was checked in a lab-scale ASSB, showing stable battery performance. This study not only demonstrates new composites of sodium-ionic, solid-state electrolytes with relatively high conductivity but also provides an anion-modulation strategy to enhance the ionic conductivity of argyrodite-type sodium solid-state ionic conductors.

Solid polymer electrolytes have been considered as promising candidates for solid-state batteries (SSBs), owing to their excellent interfacial compatibility and high mechanical toughness; however, they suffer from intrinsic low ionic conductivity (lower than 10⁻⁶ S/cm) and large thickness (usually surpassed over 100 μm or even 500 μm), which has a negative influence on the interface resistance and ionic migration. In this work, ceria quantum dot (CQD)-modified composite polymer electrolyte (CPE) membranes with a thickness of 20 μm were successfully manufactured via 3D printing technology. The CQD fillers can reduce the crystallinity of the polymer, and the oxygen vacancies on CQDs can facilitate the dissociation of ion pairs in the NaTFSI salt to release more free Na⁺, improving the ionic conductivity. Meanwhile, tailoring the thickness of the CPE-CQDs membrane via 3D printing can further promote the migration and transport of Na⁺. Furthermore, the printed NNM//CPE-CQDs//Na SSB exhibited outstanding rate capability and cycling stability. The combination of CQD modification and thickness tailoring through 3D printing paves a new avenue for achieving high performance solid electrolyte membranes for practical application in Na SSBs.