An Ultra-Fast and Ultra-Stable All-Graphene Lithium Ion Capacitor

Abstract

Lithium ion capacitors (LICs) are considered as next generation of capacitive energy storage systems , due to their 3~5 times higher energy density than traditional electrochemical double-layer capacitors. However, the battery-type anode inevitably leads to scarified power density and cycling life, due to imbalanced electrochemical performance of two electrodes, which means achieving competitive power density and cycling life simultaneously is an extreme challenge involving in the whole system. We rationally design an ultra-fast and ultra-stable all-graphene LICs, for which various graphene electrode constructions are synthesized orienting in the distinct energy storage principles of two electrodes, and a novel match approach for two electrodes is proposed and applied. Mesoporous graphene (MP-G) cathode is capable to deliver much better high-rate properties and cycling stability, edge carboxyl graphene (G-COOH) anode with expanded graphitic layer spaces enable fast pseudocapacitive and insertion capacity, as well as durability, and an optimal reaction profiles range of G-COOH are systematically determined by a novel quasi-in-situ electrochemical impedance spectroscopy (EIS) to match with MP-G. Thereby, an ultra-fast and ultra-stable LIC system (MP-G//G-COOH) is fabricated and operated in the voltage range of 1.0 ~ 4.2V. As expectedly, MP-G//G-COOH is capable to deliver an ultra-high-power density of 53550 W kg-1and an unprecedented cycling stability of 98.9% retention after 50000 cycles. This result is promising in terms of pushing ultra-fast and ultra-stable LIC system by combining ideal electrode constructions and matching approaches.