  Lithium phosphorus oxynitride (LiPON) is a well-known amorphous thin film
solid electrolyte that has been extensively studied in the last three decades.
Despite the promises to pair with Li metal anode and various cathode materials,
the presence of rigid substrate and LiPONs unique amorphous, air-sensitive
nature set limitations to comprehensively understand its intrinsic properties
for future development and applications. This work demonstrates a methodology
to synthesize LiPON in a freestanding form that exhibits remarkable flexibility
and a Young s modulus of ~33 GPa. Solid-state nuclear magnetic resonance
(ss-NMR) and differential scanning calorimetry (DSC) results with unprecedented
high signal-to-noise ratio could be obtained with such freestanding LiPON
(FS-LiPON), revealing the Li-LiPON interface bonding environments
quantitatively and a well-defined glass transition temperature for LiPON.
Combining interfacial stress and a seeding layer, FS-LiPON demonstrates a
uniform and fully dense Li metal deposition without the aid of external
pressure. Such a FS-LiPON film offers new opportunities for fundamental study
of LiPON material and associated interfaces, and provides perspectives for
interface engineering in bulk solid-state battery.
