The remarkable physicist Richard P. Feynman once said, more than fifty years ago: ”the principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are too big”. Since then (1959), human creativity and innovation have led to a paramount number of developments, opening the possibility to study, design and fabricate novel materials not only with top- down techniques, but also with bottom-up methods. Nanostructured materials and their applications to various technological fields (i.e. thin film production) are literally booming during the last decades. This is not surprising, because the search for new materials with special proper- ties is a key point to overcome the limitations posed by conventional materials and their current technological use. Nanostructures are interesting systems, since their properties often vary strongly from those of the bulk. Their reduced size influences the physical and chemical properties of the original materials. This thesis focuses on the deposition and (electro) chemical characterisation of electrode films synthesised via an aerosol-assisted route, based on electrospraying liquid precursors. Electrospray, also referred to as Electrospraying or Electrohydrodynamic Atomization (EHDA), is a versatile technique for the production of nearly-monodispersed, highly-charged droplets that, when coupled with a reaction mechanisms (i.e. pyrolysis), allows the production of a wide variety of nanostructured functional films and materials. When pyrolysis is used as reaction mechanism, the technique is usually referred to in the literature as Electrostatic Spray Pyrolysis (ESP) or Deposition (ESD), terms that will be used interchangeably throughout this thesis. Therefore, the main focus of this thesis is related to the synthesis and deposition of nanostructured thin films as electrode materials in Li-ion batteries. It will also deal with various aspects, including the effects of the deposition parameters on the properties of the deposited layers. The structure of the thesis consists of seven chapters that describe the main ideas developed in this work, being the experimental ones (Chapters 4, 5, 6 and 7) the ones that form the heart of this thesis. They are all summarized below. The aim of Chapter one is to put the research topic studied here into perspective. Thus, it presents some thoughts on sustainable energy in general and energy storage systems in particular, as well as where do they fit in the big picture of renewable energies. This discussion opens room to a brief historical overview of batteries, after which some generalities are explained and a comparison of the current available battery technologies are given. Finally, an introduction to the main topic of this thesis, namely thin film Li-ion batteries is discussed and some examples of materials readily available at the moment are highlighted. Chapter two describes the general theory of electrospray- ing and its modes of operation. The attractive features of generating charged, nearly-monodispersed droplets with tunable sizes, as well as the challenges re- lated to the increase of their production rate are discussed. This chapter intends to show the interest in industrial and laboratory applications with regard to this technique, which allows the generation of sub-micrometric droplets while working in the cone-jet and multi-jet modes. The goal of this review is to provide a summary of electrospray applications in thin solid film deposition, as well as in the field of Li-ion batteries, i.e. cathode, anode and electrolyte materials. One of the conclusions of this review, is that the temperature of the substrate, besides being needed as a synthesis parameter to obtain the desired material (i.e. by means of pyrolysis), is critical for the control of the layer uniformity and porosity. The porosity is a result of fast evaporation of the solvent, and increases with the substrate temperature. Optimal tuning of the temperature so as to obtain the desired structure without compromising the layer quality can be achieved by choosing a solvent with higher boiling temperature or by mixing several solvents. It is clear that electrospray presents advantages of uniform coating of large areas, inexpensive equipment, operation at atmospheric conditions, and easy control of deposition rate and film thickness by adjusting voltage and flow rate. Utilisation of this technique in the field of thin film battery production will surely continue to rise, and new achievements in this field can be expected in the near future. Chapter three provides an account of the different electrospray equipment used for the experiments that are described throughout this thesis, as well as which are their main differences. Moreover, a short description of a new exper imental setup designed with the purpose of handling big substrates, i.e. silicon wafers, is illustrated. Chapter four focuses on the synthesis and deposition of Fe2O3 and CuO nanostructured electrodes in one step via Electrostatic Spray Pyrolysis (ESP). It also offers some insight on possible shortcomings deriving from the conventional electrode fabrication, where the active materials (i.e. nanopowders) need to be processed in multi-step processes with polymeric binders/additives in order to cast laminated electrodes. During the processing, solutions containing precursor metal salts dissolved together with Polyvinylidene Fluoride (PVdF) binder are electrosprayed on a heated substrate where the generated submicron-sized droplets undergo pyrolysis. The oxide nanoparticles generated via pyrolysis of the metal precursors are in intimate contact with the binder contained in the emitted droplets during the electrospray process. The reacted droplets are at the same time directly driven on selected areas to form nanocomposite coated electrodes. The even inter-dispersion of the polymer binder on the nanoscale promotes the mutual adhesion of the nanoparticles in the deposits, acting at the same time as a barrier against their growth and agglomeration during both the synthesis process (i.e., inside the reacting droplets) and the electrochemical cycling, thus reinforcing the electrode and the overall contact with the current collector. Electrochemical tests demonstrate that the conver- sion reactions in these electrodes enable large initial discharge capacities, as high as 800 mAh/g and 1550 mAh/g for CuO and Fe2O3, respectively, but also reveal that capacity retention needs further improvements. It is, therefore, proposed that it is a viable approach to synthesize and assemble in one step thin nanocomposite coatings of negative electrodes at low temperature. Nevertheless, when thicker electrodes are required, it is likely necessary to include a conductive additive in the preparation, especially in presence of active mate- rials that are poor e? conductors. One important remark from this chapter relate to the known shortcomings of conversion materials, e.g., initial irreversibility, limited capacity retention and slow reaction kinetics in bulk powders, can be addressed by proper electrode preparation via ESP. Indeed, one can select dedicated precursor solutions/suspensions containing all the needed components and control the com- position, morphology, texture and thickness of the deposited composite layers with the active nanoparticles. The large voltage hysteresis between charge and discharge displayed by conversion materials is an intrinsic drawback that has been related to the energy barrier which must be overcome to break the M-X bonds (where X can be: F, O, S, or P). As a matter of fact, this phenomenon is particularly pronounced for fluorides and oxides, while sulfides and phosphides suffer less from it. Therefore, substituting oxygen with phosphine in the pro- posed synthesis process could be a possible approach to address this main issue. Moreover, the process is simple and can be conveniently optimized. Finally, it should be mentioned that this procedure, which has been carried out here on a lab scale (i.e. deposition on coin cell cans), has the potential to be implemented into a continuous, larger scale process for full fabrication of advanced nanocomposite electrodes in a roll-to-roll process by convenient outscaling of electrospray via multiple nozzle systems or equivalent equipments like the one employed for the experiments described in Chapter 5. Chapter five examines the results obtained during a large European project which consisted on the synthesis and deposition of thin film cathodes of high voltage LiNi0.5Mn1.5O4 on especially customized silicon wafers for the development of a novel 3D Li-ion microbattery. ESP, which is employed as synthesis and de- position technique, allows the production of layers with capacities up to the required capacity per square centimeter, by adjusting its thickness. Besides, when having a three-dimensional substrate surface, the thickness can be significantly reduced, according to the actual received surface area. The method in that respect also show acceptable homogeneity within the ”holes” or ”grooves” of an etched Si wafer and demonstrates its potential in the production of 3D all solid state Li-ion batteries. The influence of the synthesis parameters on the structure, texture and electrochemical behaviour of the produced electrode is investigated using different characterisation techniques. For the production of all-solid-state-microbatteries, a specific requirement of smooth, dense layers is needed. As an important conclusion in this chapter, it is found that it is not trivial to obtain an optimum set of parameters, as they all present correlation between each other. At larger distances from nozzle to substrate (2.5 - 3 cm) the stability of the spraying was better, permitting the production of a more monodisperse jet. This parameter, together with a low flow rate and a low concentration, allows the wettability of the surface so as to obtain more density of the film. Annealing of the deposited layers at 450 C improves both the cristallinity of the deposited films and the corresponding electrochemical behaviour. After this process, galvanostatic measurement yielded that the contribution to the capacity from the low voltage Mn3+/Mn4+ redox couple is reduced, while the contribution from the high voltage Ni2+/Ni4+ is increased. Even if the spinel can be formed at low temperature, high pyrolysis and/or annealing temperatures are needed to enhance the material crystal structure and thus its electrochemical behaviour. Chapter six proposes the synthesis of pure LiNi0.5Mn1.5O4 thin films followed by the application of surface modification in the form of Cr2O3 catalytic active sites, or ‘islands’. ESP is used as synthesis technique for both materials. By tuning the spray time, the covering of the underlying LiNi0.5Mn1.5O4 could be controlled and already after 10 minutes it presented almost full coverage of the cathode layer. The film morphology and structural characterisation is discussed and special attention is given to the electrochemical performance. These measurements demonstrate that, although the coating does not alter the initial spinel structure of LiNi0.5Mn1.5O4, it influences the electrochemical behaviour of the bare spinel cathode as it act as a catalyst for electrochemical processes occurring at the interface while, at the same time, improves the ionic exchange from the electrolyte into the active material enhancing the battery performance. Structural analysis of the samples before and after coating exhibit reflection characteristics only of the LNMO cubic spinel structure for all samples, indicating that the surface modification does not change the crystallographic structure of the initial cathode. However, Cr2O3 seems to be present homogeneously throughout the surface of the cathode film, as suggested by elemental mapping, instead of the active sites initially intended. XRD and EDS results, together with XAS information from similar experiments, suggest the formation of an epitaxial Cr2O3 spinel type coating. As this coating seems to be homogeneous, it opens the possibility of using LNMO-based cathodes with such modified surface together with conventional electrolyte. The above mentioned surface modifications influence the electrochemical behaviour of the bare spinel cathode. Especially, the coating sprayed for 1 minute improves the rate capability and delivers a capacity of 140 mAh/g at C/10 rate and remarkably high capacities of 108 mAh/g at 10C and 90 mAh g?1 at 20C. The epitaxial growth of a Cr2O3 coating, that takes the spinel structure of the underlying cathode, act as a catalyst for electrochemical processes occurring at the interface while, at the same time, as it is inactive towards the organic species in the electrolyte, it hinders the formation of an SEI layer improving the ionic exchange from the electrolyte into the active material enhancing the battery performance. Nevertheless, an optimum amount of Cr2O3 surface modification must be present as a good relation is needed between its catalytic activity (while, at the same time, helps at suppressing SEI layer formation) and its insulating nature. Chapter seven describes some preliminary results at building a modified AFM for in situ electrochemical characterisation of Lithium-ion battery electrode surfaces on a nanometre scale. A specific application of such technique is to know if a catalytic active site on battery electrodes, like the ones that are described in Chapter six, would render faster charge transfer. Although the machine is still far from its final aim, partial results include: - The succesful implementation of a silicon AFM probe as an electrode in a Lithium-ion battery setup. This was proven by electrochemical curves and SEM pictures. - In AFM experiments, a three-electrode setup with a LNMO sample as working electrode would be prefered. Ideally, simmultaneous control of both LNMO vs. Si and Si vs. Li would be needed in this system. A working three-electrode setup with LNMO as WE, Si as CE and Li as RE was achieved. - It is possible to prelithiate probes and store them in ambient conditions, so as to use them in a later stage. However, for storage times in the order of a month, SEM pictures do show bending of the cantilever and formation of crystals on the probe. - A topographical scan of LNMO with a lithiated probe was also accomplished. This indicates that these probes can be used for further measurements. Moreover, it was also possible to scan a similar LNMO sample immersed in liquid electrolyte with a normal (non-lithiated) probe in the AFM cell. On the other hand, a series of suggestions in order to improve the system include: - As the obtained electrochemical results were not very reproducible and showed significant noise, it is highly recommended to further improve the quality of the electrical connections. - The initially observed side reactions with moisture and air could be pre- vented by predrying all the setup parts, including the probe, and con- trolling the environment with an inert gas. - The ideal way to combine topographic and electrochemical data is to make topographic line scans and repeat these at a certain distance with a lithiated tip. A convenient distance for this has to be found. It is thought, nevertheless, that it is possible to make a modified AFM for in situ electrochemical characterization. In such a setup topographical data would be collected in the first run of the sample by a non-lithated tip. A second run at a fixed distance from the surface with a lithiated tip would then provide data on the rate of ion transport. By combining these data, it is believed it should be possible to relate surface artifacts, e.g. a coating, to increase in ionic conductivity.