Designing Novel High-Performance Anode Materials for Li-ion Batteries

Abstract

This thesis discusses original works done by Mr. Kingshuk Roy on designing unique and novel anode materials for Li-ion batteries. The overall thesis is divided into four chapters and ends with an appendix. The first chapter introduces the thesis followed by three working chapters.

Chapter 1 provides a brief idea about the global energy demand, need for renewable energy sources and efficient energy storage devices to store the energy. It also provides basic idea about the basic energy storage systems such as batteries and capacitors followed by their working principle. Although there are exist various energy storage systems of interest, this introduction chapter provides a detailed discussion of batteries, especially Li- ion battery and its working principle and the electrode materials which are being used in this device since the working chapters of this thesis are based on electrode materials for Li-ion batteries.

Chapter 2 provides an original work on the very first report of a ternary intermetallic 3D carbide with unique antiperovskite structure involving both transition (Fe) and post transition (Sn) metals, namely Fe3SnC, as a stable high capacity anode material for Li ion battery. DFT based computational studies reveal that Li insertion results in deviation from the cubic anti-perovskite structure with a volume expansion that induces significant strain in the electrode as is evident from the XRD and SAED data. We have also in-situ synthesized Fe3SnC Carbon Nano Fiber (CNF) composite and realized a very impressive cyclic stability. Initial discharge capacity was found to be 1045 mAhg-1 and along with a stable reversible capacity of 600 mAhg-1 at 200 mAg-1 and 500 mAhg-1 at 1 Ag-1 after 1000 charge discharge cycle with almost ~96% retention of capacity. Similarly, exceptionally high rate performance was observed with a high value of ~500 mAhg-1 obtained even at a current of 2 Ag-1. Fe3SnC is thus projected as a novel and very efficient material among the 3D carbide systems with the corresponding Li storage performance competing the best materials. We believe that this work will open up various new possibilities to focus on intermetallics and 3D carbide systems to be explored in the field of energy storage.

Chapter 3 provides an original work done on synthesis of an in-situ carbon encapsulated VC (VC@C) nanocomposite with three-dimensional core-shell structure by a single-step room-temperature ball milling procedure and investigation of its electrochemical performance as anodes for LIBs and SIBs. The as-prepared VC@C shows a clear promise for practical use in terms of electrochemical performance with an impressive capacity of 640 mAh g-1 after 100 discharge/charge cycles at 0.1 A g-1 for LIBs with very high reversibility. The same material also proves to be a good host for Na ions with very good rate capability and cyclic stability. Post cyclic GIXRD data prove that the reversibility and rate capability can be attributed to the robust nature of 3D carbide since the cubic structure of the material remains intact upon charging and discharging. Indeed, VC appears to be one of the most stable battery materials in the current family of anode materials. The room temperature mechano-chemical ball-milling synthesis strategy reported in this present work is facile and cost-effective and therefore, can be expected to be a promising development for the synthesis of other transition metal carbides with different morphologies for use as a potential material in energy storage devices.

Chapter 4 provides an original work on designing a SiNP based anode for Li-ion batteries with an optimal small quantity of FLBP as physical additive which has provided very impressive capacity and stability. This is a departure from the commonly used approach employing different forms of functional carbons as additives or partner materials in Si–C composites. Our approach harnesses the uniquely flexible lithiation/delithiation stress absorbing character of FLBP that is far superior to most carbon forms. Thus, very high capacity values reaching 3386 mAh g-1 and 2331 mAh g-1 at current densities of 0.1 A g-1 and 0.5 A g-1, respectively, are obtained with impressive stability measured up to 250 cycles. We believe that this work will open new avenues for possible utilization of other novel 2D materials in the alkali ion battery context.