Flexible Asymmetric Supercapacitors with Extremely Slow Self‐Discharge Rate Enabled by a Bilayer Heterostructure Polymer Electrolyte

Abstract Asymmetric supercapacitors (ASCs) with high working voltages, power density, and long cyclic life have attracted widespread interest. Along with their rapid charge process, the ASCs also exhibit fast self‐discharge behavior, which remains a big challenge. Unfortunately, very limited studies have been focused on this crucial issue. Here, a flexible asymmetric supercapacitor with excellent electrochemical performance and ultra‐long self‐discharge time is reported, which is enabled by designing a bilayer heterogeneous polymer electrolyte (HPE) of polyanions/polycations between the positive electrode and the negative electrode. The developed HPE‐based ASCs exhibit comparable electrochemical performance with those of ASCs by using homogeneous polymer electrolytes. The existing repulsive force between the charged polyelectrolytes and the movable ions can efficiently restrict the diffusion and the redistribution of the small ions, which gives the fully charged HPE‐based ASC an extremely long self‐discharge time of 110 h as the open‐circuit voltage decreases to half of its original value, over ten times longer than the devices based on homogeneous polymer electrolytes. This work indicates that the self‐discharge rate of ASCs can be efficiently suppressed by using the heterogeneous polymer electrolyte, which is helpful in the context of broadening their applications in the field of flexible electronics.