Desenvolvimento de dispositivo pseudocapacitor a base de carbono e óxidos metálicos e análises em operação utilizando espectroscopia Raman

Author(s)

Lenon Henrique da Costa

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Elétrica e de Computação
• Defense date: 2022-03-15

Examining board members

Hudson Giovani Zanin; Aline Maria Pascon; Cesar Jose Bonjuani Pagan; Gustavo Doubek; Tiago Almeida Silva

• Advisor: Hudson Giovani Zanin

Abstract

The development of energy storage devices is vital nowadays. There is an increasing demand for products and energy generation sources using supercapacitors and batteries, such as electric vehicles and wind power. Supercapacitors suffer from low energy density, but they provide high power density and can be charged and discharged hundreds of thousands of times. In this sense, this work aims at developing a device that combines non-faradaic double-layer reactions (typical of supercapacitors) and faradaic pseudocapacitive reactions (typical of batteries). Flexible and self-supporting multi-walled carbon nanotubes (MWCNTs) electrodes were produced and functionalized by oxygen-plasma (OPF) treatment. The as-prepared and OPF treated electrodes were studied by electrochemical methods in a symmetric configuration using a neutral aqueous electrolyte. The MWCNTs were also used as a scaffold for flexible and self-supported activated carbon (AC) electrodes, a capacitive porous material with a high surface area, and orthorhombic niobium pentoxide (T-Nb2O5), a pseudocapacitive material due to the rapid intercalation of Li+ ions. These two types of electrodes were analyzed by electrochemical methods in asymmetric configuration and using an organic electrolyte. These devices' development also depends on advances in understanding the chemical phenomena at the electrodes' surface and the electrode/electrolyte interface. For this reason, in situ and operando Raman spectroscopy studies were performed, focusing on the T-Nb2O5 pseudocapacitance reactions (negative electrode). Results of the present study confirm that high surface area carbon electrodes can improve the electrical characteristics of supercapacitors. Especially MWCNTs, which provide high power densities and present excellent electrical properties, have been proved a great scaffold. That is why they were used together with AC and T-Nb2O5. Although a higher increase in energy storage was initially expected with the plasma-induced surface changes, MWCNTs per se suffer from low energy density because their inner multiples walls are not electrically active. However, a theoretical model was proposed to understand the distributed capacitance behavior and the influence of the electrolyte resistance inside the different pores on the charge-storage process. Time constants involved in each process need to be considered in the interaction between faradaic and non-faradaic reactions, i.e., between capacity (Coulomb) and capacitance (Farad). The distributed capacitance applied to pseudocapacitance devices and electrodes has been proved an excellent way to assess and enable this complex interaction. The T-Nb2O5 allows a fast faradaic reaction of lithium-ion diffusion throughout the bulk of the active material. The operando Raman analysis was crucial for clarifying the electrochemical mechanisms of the material and its surface, as well as the Li+ intercalation potentials at asymmetric configuration. Typical battery electrodes and essentially capacitive electrodes were successfully combined. The T-Nb2O5 intercalation pseudocapacitance reaction was fast enough to enable a high-power energy storage device. It stores 45% and ~2.5 times more energy than an AC based supercapacitor, considering charge-discharge times between 5 seconds and 2 minutes, respectively, in the same conditions and with similar power capabilities (AU)

• FAPESP's process: 17/19222-4 - Development of storage and supplier device of electric power and methodology of dynamic analysis in operation mode
• Grantee: Lenon Henrique da Costa
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)