Novel Secondary Batteries And Advanced Materials For Sodium And Sodium-ion Energy Storage

Lithium ion batteries (LIBs) were successfully introduced into the market by Sony in1990, and have been used for the special application of low power portable devices. Recently studies has pointed out that the development of LIBs in the potential mass market of electric vehicle or hybrid electric vehicle in the future might be restricted by lithium source shortage. Thus, rechargeable batteries based on sodium and sodium ions (i.e. sodium ion battery (SIB) and sodium air battery (SAB)) have been considered as important potential candidates to partially replace LIBs. These batteries are benefited from the abundant sodium sources, cheap sodium metal and salts, and the low manufacture costs. In this study, the author will focus on both of the two aspects:SIBs and SABs. In the first part, in order to overcome the fact that SIBs suffer from the lack of suitable electrode materials with large capacity and high energy density, it is essential to learn from the successful experience of LIBs. In LIBs, Li-driven conversion reactions leading to M-O based electrodes with outstanding capacity gains over classical insertion electrodes. These reactions, which are taking advantage of electrochemistry at the nano-scale, have been extended to other classes of materials such as binary metal sulphides, nitrides, phosphides and fluorides. In this work, an attempt to extend the investigation of electrochemical properties of nanostructured thin film electrodes of these metal compounds investigated in SIBs will be made. The legitimate question remains whether these nanostructured metal compounds could undergo Na-driven conversion reactions reversibly, which means larger capacity as mentioned. In this study, Sb2O4, Fe2(MoO4)3and CUWO4thin film electrodes are prepared by radio frequency sputtering. To characterize the physical and chemical property of these thin film electrode, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) have been used. Their electrochemical performance of thin film electrodes are evaluated by galvanostsic cycling and cyclic voltammograms. These works can enrich the understanding on electrochemistry of various compound with nano scale versus sodium based and elucidating their electrochemical reaction with sodium.In the second part, the author first proposed, designed and tested a model sodium air battery working under room temperature in the world. Different electrolytes and catalysts have been also investigated.Following concepts will be discussed in the thesis:Chapter1:Introduction and Backgrounds.Chapter2:Experiment and MethodsChapter3:The electrochemical behavior of magnetron sputtered thin film antimony oxide Sb2O4as anode materials for sodium ion battery (SIB) was investigated for the first time. The Sb2O4thin film electrodes exhibit large reversible capacities (approximately900mAh g-1). The sodium storage mechanism of Sb2O4was revealed by ex situ XRD, TEM and SAED measurements. The discharging processes of Sb2O4electrode are the combination of the transformation from Sb2O4to metal Sb with Na2O and the following alloying reaction of metal antimony with sodium, ending in Na3Sb. Metal antimony and antimony oxide can be reversibly generated during the charging process successively. Antimony oxide Sb2O4can be considered a promising electrode material for SIBs due to its large capacities, low and flat discharging and charging plateaus.Chapter4:NASICON-type Fe2(MoO4)3thin films have been fabricated by magnetron sputtering and are firstly investigated as positive electrode materials for sodium ion batteries. It shows a higher reversible sodium storage capacity of approximately90mAh/g and improved cycling stability than those of bulk electrode. Our results have demonstrated that Fe2(MoO4)3in the form of nanostructure such as thin film can significantly improve its electrochemical performance for sodium ion batteries.Chapter5:Copper tungstate thin films are fabricated by magnetron sputtering and tested as positive electrode for sodium ion batteries. Similarly as the reversible copper extrusion/insertion reaction mechanism found in lithium ion batteries, electrochemical displacement reaction of sodium insertion into CuWO4involve the extrusion of copper, which can reversibly inject into the discharging product Na2WO4to form CuWO4during the charging process. CuWO4thin film electrode possesses large theoretical and practical initial capacity. Nevertheless, its cyclic performance would be limited due to the copper dissolution in the electrolyte.Chapter6:A novel type of rechargeable sodium-air battery (SAB) working at room temperature was constructed and investigated for the first time. The typical gravimetric capacities of the air electrodes (diamond like carbon thin films) are1884mAh/g at1/10C and3600mAh/g at1/60C, respectively, which are significantly superior to intercalation-based cathode materials for rechargeable sodium batteries ever reported. The reaction mechanisms in the sodium-air battery are investigated and discussed. The high reversible capacity and relevant high output voltage (about2.3V) of the room temperature SAB make it a potential alternative battery in the future.Appendix1:Carbon-coated LiCoPO4nanoparticles have been successfully synthesized by combining a facile hydroxide precipitation and the solid-state reaction method. The nanoparticles and carbon-coated structure are revealed by scanning electron microscopy and high resolution transmission electron microscopy with selected area electron diffraction measurements. The performance is benefited from the nanostructure and carbon-coating of LiCoPO4, making them as promising cathode materials for lithium ion battery.Appendix2:The lithium electrochemistry of Mn3N2thin films fabricated by magnetron sputtering has been investigated by galvanostatic cell cycling and cyclic voltammetry for the first time. The electrochemical reaction mechanisms involving the irreversible conversion from Mn3N2to Mn and Li3N in the first discharging process and the reversible transformation between Mn with Li3N and subsequent cycles were proposed. The high reversible capacity, good cycle performance and low polarization of Mn3N2film electrode makes it potential anode material for future lithium-ion batteries.