3D-Electrode Architecture of Fe2O3 – a Conversion Type Anode Material for Sodium Ion Cells

Bhar, Madhushri and Martha, Surendra Kumar (2018) 3D-Electrode Architecture of Fe2O3 – a Conversion Type Anode Material for Sodium Ion Cells. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

Over the last couple of decades’ energy has become the central focus of the modern economy. Energy security and efficiency has become a priority for the national strategic needs. The access to energy is very critical to the wealth, life style and image of every country. The effect of globalization, population increase and rising consumer demands across developed and developing countries have resulted in an exponential increase in energy consumption. This has significantly increased the gap between energy production and demand over the last several decades. Fundamental breakthrough in clean energy research is needed to solve the problem of such magnitude. Innovations in materials and processing technology provide significant opportunities for transitioning from fossil based sources to clean energy sources such as nuclear, wind and solar energy. Renewable energy sources like solar and wind provides time-varying, somewhat unpredictable energy supply, which must be captured and stored until demanded. Success of these technologies relies on development of efficient energy storage materials that can be utilized in smart batteries and capacitors. Fuel cells offer another alternative clean energy but would probably require further research in bringing down the cost for mass market. Rechargeable batteries are most promising, fulfilling the criteria of low cost, high energy density and safety issues. Secondary lithium ion batteries are very much successful in large scale portable electronic applications from its first commercialization since 1990. But the limited lithium resources and increase in market price on demand, make sodium ion battery (NIB) of its best alternative because of its high abundance and having almost similar structural and electrochemical properties to lithium ion battery.Usually transition metal oxides (NaMO2, M=Co, Mn) phosphates (NaFePO4) used as cathode material and insertion type (hard carbon), conversion type (oxide, sulfide based) and alloy type (Na3Sn, Na3Sb) are used as anodes s in NIB. Among them, Fe2O3 is of main interest due to its high theoretical capacity (~1007 mAhg-1) and high abundance. Nano-structured Fe2O3 was prepared by precipitation method which shows initial discharge capacity at 419 mAhg-1 at 20 mAg-1. But these conversion type anode materials have material issues during cycling such as pulverization for Na+ insertion and de-insertion in charge-discharge cycles resulting low capacity and low cycling performance. In this work we studied synthesis and electrochemical performance of carbon-coated Fe2O3 using conducting p-pitch as source of carbon. To further enhance its electrochemical performance, 3D electrode architecture based anodes ware prepared using 3D carbon fiber mats where the porous conducting carbon matrix act as a buffer during volume change. It shows the reversible capacity of 725 mAhg-1 with stable capacity retention. The material was characterized by XRD, RAMAN, SEM, TEM and electrochemical performance was analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopic studies. Thus, preparing the material in nano-scale, improving conductivity of active material through carbon coating and 3D electrode architecture improve electrochemical performance in presence of porous conducting carbon network and accommodating volume changes for Na+ insertion and de-insertion during charge-discharge cycles.

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