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.

Revealing the Mechanism of Bilayer Heterogeneous Polyelectrolytes to Suppress the Self‐Discharge of Symmetric Supercapacitors

“…The optimal ratio was previously optimized by our group as following. [ 36 ] 1) The pure CNTs films were immersed in concentrated nitric acid for 12 h to remove impurities and then were treated with oxygen plasma for 5 min to improve the hydrophilicity of CNTs films. 2) The treated CNTs film was used as the working electrode for electrochemical deposition, where a platinum sheet and a saturated calomel electrode (SCE) were used as counter electrode and reference electrode, respectively.…”

“…[33][34][35] Recently, we for the first time introduced the bilayer heterogeneous polyelectrolyte (BHP) building by a layer of polycation complex and a layer of polyanion complex to construct two-electrode supercapacitors, which exhibited interesting suppressed effect to slowdown the self-discharge process of devices. [36,37] However, the insightful mechanism of how do the polyelectrolyte complexes affect on the electrochemical performance and self-discharge behavior of the BHP-based supercapacitors is still unclear. In this work, we designed a series of bilayer heterogeneous polyelectrolytes by using various polycation and polyanion complexes with different structures and properties and systematically investigated their effects on the electrochemical performance and self-discharge behaviors from the experimental and theoretical views.…”

Conjugated supercapacitor with suppressed self‐discharge constructed by pairs of prelithiated Nb2O5@C with optimized elemental and phase purity in the carbon shell

“…The ambitious goal of carbon neutralization calls for high‐performance energy storage systems. [ 1,2 ] Supercapacitors have become a considerable alternative to rechargeable batteries [ 3–6 ] due to their high power density and cycle stability, especially for applications that require instantaneous high power density and short‐term energy storage, [ 7–11 ] such as the gantry cranes that need to quickly grab cargo in ports. Despite numerous advantages, self‐discharge is one of the key problems which limits the wider applications of conventional electrochemical double‐layer capacitors (EDLCs).…”

A novel bilayer heterogeneous poly(ionic liquid) electrolyte for high-performance flexible supercapacitors with ultraslow self-discharge

“…24,25 More recently, heterogeneous polyelectrolytes formed by a layer of polyanion complex and a layer of polycation complex have a unique current rectification effect, 31,32 which exhibited an interesting suppressed effect on the self-discharge of flexible supercapacitors due to the electrostatic interaction force between movable ions accumulated on/in electrodes and the charged polyelectrolytes. 33,34 However, the low dissociation potential of water (1.23 V) endows the aqueous heterogeneous polyelectrolyte-based supercapacitors with a limited potential window and low energy density. [33][34][35][36] In this regard, poly(ionic liquid)s (PILs) with excellent thermal and mechanical properties of polymers also reserve the low vapor pressure and wide potential window of ionic liquids (ILs), [37][38][39] which represents a promising type of polymer gel electrolyte for high-performance flexible supercapacitors.…”

“…33,34 However, the low dissociation potential of water (1.23 V) endows the aqueous heterogeneous polyelectrolyte-based supercapacitors with a limited potential window and low energy density. [33][34][35][36] In this regard, poly(ionic liquid)s (PILs) with excellent thermal and mechanical properties of polymers also reserve the low vapor pressure and wide potential window of ionic liquids (ILs), [37][38][39] which represents a promising type of polymer gel electrolyte for high-performance flexible supercapacitors. 40,41 Therefore, flexible supercapacitors with a wide potential window and slow selfdischarge rate may be achieved by designing a novel bilayer heterogeneous poly(ionic liquid) electrolyte (BHPE), but no relative research studies have been reported so far.…”