Polyimide‐Based Self‐Standing Polymer Electrolyte Membrane for Lithium‐Ion Batteries

A new solid polymer electrolyte composed of a polyimide matrix, an ionic liquid additive (1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide, [Bmim][TFSI]), and a lithium salt (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) is fabricated by the solution‐casting technique. The obtained self‐standing polyimide (PI)‐based polymer electrolyte (PI‐100 %BmimTFSI‐60 %LiTFSI) membranes show a great flexibility, transparency, and infiltration ability. As a result of the high thermal stability of the polyimide matrix, the thermal decomposition temperature of the electrolyte is high (420 °C). The ionic conductivity can be up to 1.73×10 −5  S cm −1 at room temperature and reaches 1.26×10 −3  S cm −1 at 80 °C. In addition, the PI‐100 %BmimTFSI‐60 %LiTFSI electrolytes have a wide electrochemical stability window of 4.8 V, a general lithium ion transference number of 0.12, and good interfacial stability and compatibility. In particular, the assembled LiFePO 4 /Li half cells made from this polyimide‐based electrolyte can light up a light‐emitting diode lamp at room temperature.