Conformal zwitterionic polymer nanofilms and lithium batteries

Scalable synthesis of electrochemically inert nanofilms with precise spatial and compositional control enables rational design of solid-electrolyte interphases (SEIs) in rechargeable batteries. Ion and molecule transport through SEIs largely determines the cycling stability of high-energy rechargeable metal and metal-ion batteries, where electroreduction during charging often occurs beyond electrolyte stability limits. We report nanometer-thick gradient zwitterionic polymer (G-ZWP) interphases, synthesized via a scalable solvent-free method, to regulate transport and electroreduction kinetics at Li-metal anodes, achieving stable cycling. The synthesis combines initiated chemical vapor deposition and diffusion-limited vapor derivatization to form a zwitterionic top layer with high ionic conductivity and an inner covalently cross-linked layer blocking solvent access while remaining stable at reducing potentials. Cu substrates with G-ZWP interphases show >2000-hour cycling at 1 milliampere per square centimeter [6 milliampere hours per square centimeter (mA·hour/cm²)]. The interphases also enable long-term cycling of Li batteries (N/P = 0 to 2.5) and Li–dry-air batteries (10 mA·hour/cm²) and stabilize Na/Zn electrodeposition.