Supercapacitors (EDLCs) are electrochemical energy storage (EES) devices, which can provide ultra-high power density and ultra long cycle life. Kaskel and others put forward the concept of supercapacitor diode (capode) in 2019, which integrates the characteristics of diode into EDLC. Capode can only provide energy storage capability for one charging direction, thus extending the traditional supercapacitor to new technology application fields, and playing an important role in power grid stability, signal propagation and logic operation. However, current capode devices require that carbon electrodes have strict pore size engineering, which greatly increases the manufacturing cost and complexity of porous carbon (especially pure microporous carbon). Secondly, capode can only realize charge storage in the positive bias direction. Due to the lack of suitable electrolyte systems with large size anions and small size cations, the construction of reverse capode is very challenging. Recently, Yan Xingbin of Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Tang Yu of Lanzhou University and others cooperated to realize capodes device with adjustable bias direction by using polycation based ionic liquid (IL) or polyanion based ionic liquid as electrolyte, which represents a major breakthrough in the design of high-performance capacitive ion diode. This study is entitled "construction of supercapacitor based ionic diodes with adjustable bias directions by using poly (ionic liquid) Electronics" and published in the latest issue of advanced materials.

Highlights:

1. By assembling asymmetric supercapacitors with commercial activated carbon, and using one of two kinds of polyionic liquids (polycationic pvbim · (TFSI) n or polyanionic (EMIM) n · pstfsi) as electrolyte, capode with forward or reverse bias charging capability was successfully constructed.

2. The cations in pvbim · (TFSI) n and the anions in (EMIM) n · pstfsi are confined in the organic network, but their counter ions can move freely under the potential. Therefore, the capodes can only provide high capacitance in the positive or negative bias direction, and show up to 80% rectification ratio and excellent cycle life (4500 cycles).

Preparation and characterization of two kinds of polyionic liquids

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