Designing New Polyurethane‐Based Solid Polymer Electrolytes for Flexible Solid‐State Supercapacitors

Solid polymer electrolytes are considered as key materials in flexible solid‐state supercapacitors. In this work, the polyurethane‐based solid polymer electrolytes were obtained from polyurethane elastomer prepared from toluene diisocyanate (TDI) based prepolymer PFL100 and 3,3′‐dichloro‐4,4′‐diaminodiphenylmethane (MOCA) as polymeric matrix impregnated with lithium tetrafluoroborate LiBF 4 solution in N ‐Methyl‐2‐pyrrolidone (NMP). The swelling degree, mechanical properties and ionic conductivity of the polymer electrolytes were shown to strongly depend on the concentration of LiBF 4 in NMP. The polymer impregnated with the lithium salt solution containing 7 wt.% LiBF 4 (PU‐PFL100) has the optimal mechanical properties, high ionic conductivity (nearly 5 × 10 −4 S cm −1 at 25°C) and was tested as the solid polymer electrolyte for flexible solid‐state supercapacitors with MXene‐activated carbon (MXene/AC) composite electrodes. Symmetrical (MXene/AC//PU‐PFL100//MXene/AC) and asymmetrical (MXene/AC//PU‐PFL100//Li 4 Ti 5 O 12 ) supercapacitor cells were tested in which PU‐PFL100 was used as an electrolyte‐separator. Cyclic voltammetry (CV) and galvanic charge–discharge (GCD) experiments showed that the supercapacitor cells can deliver a specific capacitance about 40 F g −1 at room temperature and PU‐PFL100 can be successfully used in the flexible solid‐state supercapacitors.