Directly Grown nanostructured electrodes for high volumetric energy density binder-free hybrid supercapacitors: A case study of CNTs//Li 4 Ti 5 O 12

Abstract

Hybrid supercapacitor (HSC), which typically consists of a Li-ion battery electrode and an electric double-layer supercapacitor electrode, has been extensively investigated for large-scale applications such as hybrid electric vehicles, etc. Its application potential for thin-film downsized energy storage systems that always prefer high volumetric energy/power densities, however, has not yet been explored. Herein, as a case study, we develop an entirely binder-free HSC by using multiwalled carbon nanotube (MWCNT) network film as the cathode and Li 4 Ti 5 O 12 (LTO) nanowire array as the anode and study the volumetric energy storage capability. Both the electrode materials are grown directly on carbon cloth current collector, ensuring robust mechanical/electrical contacts and flexibility. Our 3â ...V HSC device exhibits maximum volumetric energy density of ∼4.38â ...mWh cm â 3, much superior to those of previous supercapacitors based on thin-film electrodes fabricated directly on carbon cloth and even comparable to the commercial thin-film lithium battery. It also has volumetric power densities comparable to that of the commercial 5.5â ...V/100â ...mF supercapacitor (can be operated within 3â ...s) and has excellent cycling stability (∼92% retention after 3000 cycles). The concept of utilizing binder-free electrodes to construct HSC for thin-film energy storage may be readily extended to other HSC electrode systems.