Rational design of nanostructured electrodes for Li-ion batteries

QD Chemistry

Vidal Laveda, Josefa ; Engineering & Physical Sciences Research Council (EPSRC) ; Corr, Serena

University:University of Glasgow

Department:School of Chemistry

关键词: Microwave synthesis, nanostructured electrodes, Li-ion batteries, single source precursors, metal alkoxides, olivines, transition metal oxides.;   

Others  :  http://theses.gla.ac.uk/8051/1/2017VidalLavedaphd.pdf

来源: University of Glasgow

【 摘 要 】

This thesis focuses on the rational design of fast and low temperature synthetic routes for the preparation of energy storage nanostructures with potential applications as electrode materials for Li-ion batteries. The materials synthesised in this work have been fully investigated by powder X-ray diffraction, electron microscopy and potentiodynamic measurements. Where possible, high resolution powder X-ray and neutron diffraction, X-ray and neutron pair distribution function (PDF) analysis and muon spin relaxation (µ+SR) studies have been conducted in order to have a better understanding of the structure-property relationship and have a complete and detailed characterisation of these battery materials. Chapter 1 includes a general introduction about Li-ion batteries and a brief analysis of the most promising electrode materials used in Li-ion batteries. Furthermore, a short description about different synthetic methodologies such as solid state, microwave-assisted and solvothermal syntheses is included. In particular, the benefits of single source precursor processes are highlighted. Finally, the main aims of this thesis are also discussed.The objective of Chapter 2 is to provide detailed experimental procedures of all materials synthesis and also to briefly describe the main characterisation techniques employed during this research, exploring in more detail those not commonly used, such as pair distribution function analysis and muon spin relaxation.In Chapter 3, a microwave-assisted solvothermal approach for the preparation of a family of LiFe1-xMnxPO4 (x=0, 0.25, 0.5, 0.75 and 1) olivines using commercial starting materials is presented. To fully characterise and have a deeper insight of the structure-property relationship of these nanocrystalline phases, high resolution powder neutron diffraction and neutron PDF analyses of these phases are conducted, allowing the examination of the local structure, cation distribution, presence of defects and Li content. Moreover, muon spin relaxation is used for the first time to investigate the lithium diffusion in this series of olivine mixed metal phosphate phases. By understanding how this double transition metal system operates, it may be possible to synthesise high performing electrode nanomaterials with higher energy density than LiFePO4 with no significant increase in cost and exhibiting charge/discharge rates acceptable for commercial applications.Chapter 4 covers a fast and energy-efficient synthetic route to olivine nanostructured LiFe1-xMnxPO4 cathodes and Mn3O4 hausmannite conversion anodes for Li-ion batteries using a new class of metal alkoxides containing one or two transition metals. The main advantage of metal alkoxides over commercially available inorganic salt mixtures is that the different metals of the final product are already present in a single precursor, which significantly reduces the energy required for reaction of a multicomponent precursor mixture employed in conventional synthesis. Furthermore, thermal decomposition of these metal alkoxide compounds can be performed at relatively low temperatures, allowing decreased temperatures during synthesis and making the process more energy efficient. This work intends to emphasise the versatility of metal alkoxide precursors in the preparation of nanostructured Li-ion battery materials for both positive and negative electrodes through relatively fast and low temperature microwave and ultrasound-assisted methods. In Chapter 5, having confirmed the suitability of employing transition metal alkoxide precursors for the preparation of nanostructured electrodes via microwave or ultrasound assisted methods, efforts have been directed to develop the synthesis of a series of heterometallic alkoxide complexes containing both Li and a transition metal (Fe, Mn). These heterometallic alkoxide precursors are then used for the generation of highly crystalline LiFe1-xMnxPO4 olivine nanostructures exhibiting an outstanding electrochemical performance. Co-location of all the required metals in these metallorganic precursors could bypass the need of diffusional mixing and allow the reactions to proceed faster and at lower temperatures generating better crystallised materials. X-ray PDF analyses of these LiFe1-xMnxPO4 olivine nanophases are conducted in an effort to examine the local structure, defect chemistry and show that microwave processes produce highly crystalline materials even after short reaction times. Finally, a ionothermal microwave-assisted synthesis of LiFePO4 nanoparticles using heterometallic alkoxide precursors has been examined in order to study the influence of the solvent in the resulting electrochemical performance.Chapter 6 explores the preparation of olivine LiFe1-xMnxPO4 nanostructures through conventional solvothermal processes using the same single source heterometallic alkoxide precursors. A reduction in particle size and an enhancement in the electrochemical behaviour are achieved when using single source precursor metallorganic compexes compared to commonly used commercial starting materials. Moreover, the fabrication of Fe3O4 magnetite nanoparticles by the room temperature hydrolysis of the [FeLi2Br(OtBu)4(THF)2]n heterometallic alkoxide precursor and its application as anode material for Li-ion batteries is presented.Chapter 7 further develops this family of heterometallic precursors by examining the preparation of olivine nanostructured Ni-doped LiFePO4 cathodes via microwave processes. The effect of the addition of polyvinylpyrrolidone (PVP) in the reaction mixture, which could act as a capping and dispersing agent to prevent particle growth and agglomeration as well as a possible carbon source for all-in-one carbon coating procedures, is investigated. The preparation of a Li and Ni containing metal alkoxide and its utilisation as a Ni precursor for the preparation of nanostructured LiFe1-xNixPO4 olivine cathodes and NiO conversion anodes is presented, demonstrating again the versatility of single source precursor synthesis using heterometallic alkoxides in the preparation of both Li-ion battery cathode and anode materials.Finally, Chapter 8 includes some general conclusions and an outlook for future work including some preliminary investigations on microwave syntheses of non-olivine β-LiFe1-xMxPO4 (M=Fe, Co, Ni) and maricite NaFe1-xMnxPO4 nanostructures for Li and Na-ion battery applications.