Fig. 4: The superiority of amorphous bulk materials and interface.

a Solid-state 23Na NMR of the pristine crystalline and the cycled amorphous Na5SmSi4O12. b 23Na NMR relaxation rate of Na cycled Na5SmSi4O12 as a function of temperature in K−1. c Nanoindentation load–displacement curves of crystalline Na5SmSi4O12 and amorphous Na5SmSi4O12. d Schematic of interface morphology evolution during sodium plating/stripping.