Layer-by-Layer Assembly of Strong Thin Films with High Lithium Ion Conductance for Batteries and Beyond

Polyethylene oxide (PEO) is one of the most widely used polymeric ion conductors which has the potential for a wide range of applications in energy storage. The enhancement of ionic conductivity of PEO-based electrolytes is generally achieved by sacrificing the mechanical properties. Using layer-by-layer (LbL) self-assembly with a nanoscale precision, mechanically strong and self-healable PEO/polyacrylic acid composite thin films with a high Li⁺ conductivity of 2.3 ± 0.8 × 10^-4 S cm^-1 at 30 °C, and a strength of 3.7 MPa is prepared. These values make the LbL composite among the best recorded multifunctional solid electrolytes. The electrolyte thin film withstands at least 1000 cycles of striping/plating of Li at 0.05 mA cm^-2 . It is further shown that the LbL thin films can be used as separators for Li-ion batteries to deliver a capacity of 116 mAh g^-1 at 0.1 C in an all-LbL-assembled lithium iron phosphate/lithium titanate battery. Finally, it is demonstrated that the thin films can be used as ion-conducting substrates for flexible electrochemical devices, including micro supercapacitors and electrochemical transistors.