(Digital Presentation) Hydrophilic and Hydrophobic Carbon Nanotubes Combined into a Buckypaper As an Electrode for Li-O2 Batteries

Abstract

With the decreasing costs of wind and solar power, these two energy sources are set to gain a sizeable share of the electricity market in the next years. To cope with the intermittency of these electricity sources, grid operators are required to develop new, inexpensive, and efficient energy storage facilities. One of the technologies being considered for such application is the Li-O2 battery, whose main advantage compared to state-of-the-art lithium-ion batteries is the prospect of higher energy density which might lead to decreased installation costs. Nevertheless, these batteries depend upon efficient mass transport of O2 inside the electrode to present suitable power density. In this work, a mix of hydrophilic and hydrophobic carbon nanotubes (CNT) was used to produce an O2 electrode with enhanced mass transport properties. Hydrophobic CNT were prepared via thermal treatment under Ar atmosphere at 850 °C for 2 h. Hydrophilic CNT were prepared via refluxing in 7 mol L-1 HNO3 solution for 4 h (~120 °C). Raman spectroscopy was used to analyze the quality of both types of CNT. Different proportions of hydrophobic and hydrophilic CNT were dispersed in solution with a surfactant using a probe sonicator. The solution was filtered using a 0.22 μm membrane and vacuum to produce a buckypaper. Batteries were assembled in a glove box using a Li electrode, a separator membrane (glass fiber), and the buckypaper as the O2 electrode. Galvanostatic discharge tests were carried out at different currents to analyze the impact of different qualities of CNT used in the making of the O2 electrode in the increasing demand for O2 in the battery at high currents. Scanning electron microscopy images were used to compare the morphology of the different electrodes before and after discharge. Results are expected to demonstrate a new method to increase the mass transport rates for O2 in Li-O2 batteries.The authors gratefully acknowledge the support from FAPESP (the Sao Paulo Research Foundation, Grant Numbers 2018/16663-2 and 2017/11958-1), Shell, the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation, and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.