Palladium-Filled Carbon Nanotubes Cathode for Improved Electrolyte Stability and Cyclability Performance of Li-O 2 Batteries

Abstract

Li–oxygen (Li-O 2) cathodes using palladium-coated and palladium-filled carbon nanotubes (CNTs) were investigated for their battery performance. The full discharge of batteries in the 2–4.5 V range showed 6-fold increase in the first discharge cycle of the Pd-filled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled also exhibited improved cyclability with 58 full cycles of 500 mAh · g −1 at current density of 250 mA · g −1 versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. In this work, the effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, FTIR, XRD, UV/Vis spectroscopy and visual inspection of the discharge products using scanning electron microscopy confirmed the improved stability of the electrolyte due to this encapsulation and suggest that this approach could lead increasing the Li-O 2 battery capacity and cyclability performance. High energy density batteries have garnered much attention in re-cent years due to their demand in electric vehicles. Lithium oxygen (Li-O 2) batteries have nearly 10 times the theoretical specific energy of common lithium-ion batteries and in that respect have been regarded as the batteries of the future. 1–3 A typical Li-O 2 battery consists of Li anode, porous cathode open to, oxygen and Li + ion conducting electrolyte separating the electrodes. Li-O 2 battery stores energy via a simple electrochemical reaction (2Li + O 2 ↔ Li 2 O 2) in which Li 2 O 2 is deposited on the surface of cathode via the forward reaction (oxygen reduction reaction, ORR) during discharge and backward reaction (oxygen evolution reaction, OER) takes place during charg-ing to decompose Li 2 O 2 on the surface of cathode. 2 Since the main discharge product (Li 2 O 2) and other discharge/charge byproducts in Li-O 2 batteries are electrically insulating and not soluble in elec-trolytes, the structure and electronic conductivity of cathode materials have been critical factors in determining the limiting capacity of Li-O 2 batteries. 4,5 Carbonaceous materials such as carbon nanoparticles,