Freestanding LiPON: from Fundamental Study to Uniformly Dense Li Metal Deposition Under Zero External Pressure

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 enable Li metal anode and various cathode materials, the presence of rigid substrate and LiPON’s unique amorphous, air-sensitive characteristics set limitations to comprehensively understand its intrinsic properties for next-stage advancement and applications. This work demonstrates a different methodology to synthesize LiPON in a freestanding form that removes the substrate. The freestanding LiPON (FS-LiPON) exhibits remarkable flexibility, with controllable film thickness and large-scale production compatibility. Benefited from the freestanding form, solid-state nuclear magnetic resonance (ss-NMR) and differential scanning calorimetry (DSC) are able to attain high S/N ratio to determine the local bonding structures and glass transition temperature of LiPON. In the presence of 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 provide perspectives for interface engineering in bulk solid-state battery.