Lithium titanate/pyrenecarboxylic acid decorated carbon nanotubes hybrid - Alginate gel supercapacitor

Abstract

A facile scalable strategy is reported for the synthesis of a hybrid of lithium titanate (Li\n4\nTi\n5\nO\n12\nor LTO)and 1-pyrenecarboxylic acid decorated multiwalled carbon nanotubes (PCA@CNTs). LTO platelets comprising of quasi-spherical nanoparticles afford short diffusion paths for electrolyte ions. PCA@CNTs, enhance the electrical conductivity of the nearly insulating LTO by 3 orders of magnitude, thus maximizing the ion-uptake capability of the hybrid. Symmetric and asymmetric supercapacitors with the LTO/PCA@CNTs hybrid supported over Ni foam substrates are assembled with a novel Li\n+\nconducting alginate gel, in air without any inert conditions that are typically used for all LTO based devices. The gel shows an average ionic conductivity of ∼8.4 mS cm\n−1\nat room temperature, and is found to be electrochemically stable over a wide operational voltage window of ∼2.5 V. Benefitting from the synergy of electrical double layer (EDL)storage afforded by PCA@CNTs, ion-storage by LTO through a redox reaction and EDL, and the ease ion-movement across the cell due to the open architecture of CNTs, the asymmetric LTO/PCA@CNTs hybrid cell outperforms the symmetric cells by a large margin. The best areal specific capacitance (SC), volumetric SC and energy density are ∼54 mF cm\n−2\n, ∼4.3 F cm\n−3\n(at 0.5 mA cm\n−2\n)and ∼3.7 mWh cm\n−3\n(at a power density of 49.6 mW cm\n−3\n)significantly enhanced for the asymmetric LTO/PCA@CNTs hybrid cell, compared to the symmetric- PCA@CNTs and hybrid cells. The design is simple to implement and can serve as a prototype to develop a range of yet unexplored LTO/carbon nanomaterial based supercapacitors.