Studies on Mono- and Multi-valent Ion Storage Using Metal Phosphosulfide and Organic Carbonyl Compounds

Abstract

The present study describes the results on inorganic and organic materials for energy storage and sensors. It contains eight chapters including introduction, experimental and summary sections. The first chapter gives a brief overview of energy storage systems, progress and challenges associated with them along with a few possible solutions to tackle them. The second chapter explains all the experimental details like chemicals used, syntheses procedures, instruments used, and various processes and procedures used in this work. The third chapter demonstrates the ion storage performance of copper phosphosulfide. As an anode for Li-ion battery, it delivers a high capacity and high cycling stability. The pre activated electrode delivers very high stable capacity. The capacity offered by the phosphosulfide is higher than that of the corresponding phosphide and sulfide that indicates the importance of the presence of both P and S in the structure. The mechanism as investigated by in situ Raman spectroscopy and other ex situ techniques suggest a conversion reaction and formation of a thick SEI like film on the electrode surface. As prepared material shows good performance for Mg-ion battery with moderate rate capability. A further improvement in the capacity and importantly the rate performance is achieved by utilizing a multiwall carbon nanotube composite. The composite electrode further delivers high cycling stability at high current rates. Moderate performance is observed for Al-ion battery which may be due to its high charge to size ratio that makes the insertion / extraction process rather slow. The fourth chapter utilizes organic carbonyl compounds as electrodes for mono- and multi-valent metal ion batteries. A layer type, slight off planar polymer is synthesized from benzoquinone and pyrrole and explored as a universal cathode for Li, Mg, Zn and Al-ion batteries. Thousands of stable cycles are observed for all these systems even at very high current rates and show excellent rate performance. For Li-ion battery, the cell performance is studied at high rates of 10 A g-1 which takes only 22 s to charge and discharge. For Mg-ion battery, an alternate alloy anode (AZ31) is explored, and 5000 cycles are observed even at a high current rate of 2 A g-1 . Similarly, for Zn-ion battery, along with good rate performance, a long-term stability of 20000 cycles is achieved at 2 A g-1 . More importantly, even for a more difficult Al-ion system, thousands of stable cycles are obtained at high rates of 0.5 and 1 A g-1 with 100% capacity retention. A surface controlled pseudocapacitive contribution to the overall capacity is responsible for such high performance in all the cases. The off planar geometry is expected to facilitate ion diffusion process thereby resulting in high rate and high performance. Ex situ infrared and X-ray photoelectron spectroscopy measurements show functional group transformation during the ion storage process. Further, an organic dye, vat orange 11 consisting of three conjugated anthraquinone units is studied for Mg- and Zn-ion batteries. It shows better performance than that of a single anthraquinone unit highlighting the benefit of conjugation. Different carbon additives and electrolytes are investigated further to achieve high performance for Mg-ion battery. A capacity fading is observed for Zn-ion battery due to high solubility of the dye in the electrolyte. The fifth chapter explores a few non-nucleophilic electrolytes for Mg-ion batteries with wide electrochemical stability window. It is observed that Mg(HMDS)2 and AlCl3 in a mixture of glymes with ionic liquid additive shows high deposition/ dissolution efficiency with low overpotentials and excellent oxidation stability on a few common substrates. Further, the electrolyte speciation study is carried out with the help of Raman and 27Al NMR spectroscopy. A non-aqueous Li-O2 battery is studied using tin phosphosulfide (SnPS3) as air cathode in the sixth chapter. High cycling performance and low charge-discharge overpotential is observed for the rGO composite as compared to the pristine material. High electronic conductivity and high surface area of rGO is believed to enhance the performance and Li2O2 is obtained as the discharge product. The seventh chapter investigates the gas sensing applications and photodetection activity of Cu3PS4. It is very sensitive towards NH3 gas compared to other analyte gases and can detect as low as 17 ppb with a high response of 160 % for 10 ppm NH3. It shows a fast response and excellent reversibility under ambient conditions. Good sensing properties for NO2 gas has been observed. Preliminary photodetector studies reveal that the phosphosulfide can be used for UV-vis photodetection. The last chapter summarizes the thesis work and gives some future directions to improve the performance further and design new systems. At the end, two appendixes are given where an ionic liquid, 1-ethyl-3-vinylimidazoilum bis(fluorosulfonyl)imide (EVImFSI) containing lithium bis(trifluorosulfonyl)imide (LiTFSI) is used as a wide potential window (~5 V) electrolyte for Li-ion battery and nickel phosphosulfide (NiPS3) is used as electrocatalyst for electrochemical nitrogen reduction to ammonia (NH3).