Studies of Functional Defects for Fast Na-Ion Conduction in Na3-yPS4-xClx with a Combined Experimental and Computational Approach

All-solid-state rechargeable sodium (Na)-ion batteries are promising for inexpensive and high-energy-density large-scale energy storage. In this contribution, new Na solid electrolytes, Na3-yPS4-xClx, are synthesized with a strategic approach, which allows maximum substitution of Cl for S (x = 0.2) without significant compromise of structural integrity or Na deficiency. A maximum conductivity of 1.96 mS cm(-1) at 25 degrees C is achieved for Na3.0PS3.8Cl0.2, which is two orders of magnitude higher compared with that of tetragonal Na3PS4 (t-Na3PS4). The activation energy (E-a) is determined to be 0.19 eV. Ab initio molecular dynamics simulations shed light on the merit of maximizing Cl-doping while maintaining low Na deficiency in enhanced Na-ion conduction. Solid-state nuclear magnetic resonance (NMR) characterizations confirm the successful substitution of Cl for S and the resulting change of P oxidation state from 5+ to 4+, which is also verified by spin moment analysis. Ion transport pathways are determined with a tracer-exchange NMR method. The functional detects that promote Na -ion transport are maximized for further improvement in ionic conductivity. Full-cell performance is demonstrated using Na/Na3.0PS3.8Cl0.2/Na3V2(PO4)(3) with a reversible capacity of approximate to 100 mAh g(-1) at room temperature.