473 research outputs found
Patterning dye-sensitized solar cell photoanodes through a polymeric approach: A perspective
No full textPerformances in terms of efficiency and stability of dye-sensitized solar cells (DSSCs) depend on several factors related to the preparation of the device components (electrodes and electrolyte). In particular, patterning techniques recently intruded in the third generation photovoltaic scenario with promising results. In this perspective, we introduce the most interesting strategies proposed for the patterning of photoanodes and cathodes. Afterwards, we propose a novel approach exclusively based on the use of polymeric materials. The resulting DSSC shows a power conversion efficiency equal to 5.33% measured under 1 sun irradiation, and retains the 96% of this value in a prolonged aging test (2000 h at 50 °C)
Insights into the Development and Performances of Ionogel-Based Electrolytes for Solid-State Lithium-Based Batteries
No full textSolid-state electrolytes (SSEs) aim to overcome safety issues, decrease package volume, and increase the energy density of next-generation energy storage devices, such as Li-ion and post-lithium batteries. Among different types of SSEs, the ionogel (or ion gel) systems, in which polymer electrolytes are doped with room-temperature ionic liquids (RTILs), are amongst the most attractive choices to reach ionic conductivity values comparable to those of liquid electrolytes, ensuring better safety and electrode/electrolyte interface stability [1]. In our previous studies, several ionogel samples were prepared by in-situ UV-curing [2]. Here, we present the results of newly optimized methacrylate-based solid-state electrolyte systems conceived for ambient temperature cycling with high-energy cathodes. We characterized the electrolyte formulations using various physico-chemical and electrochemical methods, including gel content, FTIR, rheology, DMTA, TGA, SEM, voltammetry, impedance spectroscopy, and galvanostatic cycling. The focus is particularly on the influence of using two different RTILs as reaction media on the properties of the resulting materials and their electrochemical behaviours. The achieved results indicate that viscosity affects the polymerization kinetics of the ionogels, which in turn affects their thermal stability and galvanostatic cycling behavior. The obtained ready-to-use and self-standing crosslinked ionogel electrolyte membranes (~100 μm thickness) showed relatively high ionic conductivity (0.8 to 2 mS/cm at 20 °C) and anodic stability (up to 4.5-5 V vs. Li). Lithium lab-scale cells were assembled with ionogel-polymerized-on-NMC-cathodes for galvanostatic cycling measurements, and they demonstrated initial discharge capacities of around 180 mAh/g at low C-rate in the voltage range of 3.0-4.3 V at room temperature. Furthermore, motivated by the demand of increasing the overall performance of the SSEs, different types of composite solid electrolytes are now under our investigation and further development, including the utilization of active and inert inorganic fillers. For example, we introduced LLZO ceramic microparticles into the aforementioned ionogel systems for fabricating composite SSEs via in-situ photopolymerization. So far, the best achieved preliminary cycling results show enhanced and more stable cycling behaviour at higher C-rates up to 0.2C at room temperature, suggesting the promising prospects of our composite SSEs and their potential contribution to the fabrication of solid-state, high-energy lithium-based batteries
Mesoporous Si and multi-layered Si/C films by Pulsed Laser Deposition as Li-ion microbattery anodes
No full textSilicon is a very attractive Li-ion battery anode material due to its high theoretical capacity, but proper nanostructuring is needed to accommodate the large volume expansion/shrinkage upon reversible cycling. Hereby, novel mesoporous Si nanostructures are grown at room temperature by simple and rapid Pulsed Laser Deposition (PLD) directly on top of the Cu current collector surface. The samples are characterised from the structural/morphological viewpoint and their promising electrochemical behaviour demonstrated in lab-scale lithium cells. Depending on the porosity, easily tuneable by PLD, specific capacities approaching 250 μAh cm−2 are obtained. Successively, newly elaborated bicomponent silicon/carbon nanostructures are fabricated in one step by alternating PLD deposition of Si and C, thus resulting in novel multi-layered composite mesoporous films exhibiting profoundly improved performance. Alternated deposition of Si/C layers by PLD is proven to be a straightforward method to produce multi-layered anodes in one processing step. The addition of carbon and mild annealing at 400 °C stabilize the electrochemical performance of the Si based nanostructures in lab-scale lithium cells, allowing to reach very stable prolonged reversible cycling at improved specific capacity values. This opens the way to further reducing processing steps and processing time, which are key aspects when upscaling is sought
On the impact of electrolyte temperature on contact glow discharge electrolysis
No full textThis study aims at disclosing the effect of small temperature drops (10-15 degrees C) of the electrolyte on Contact Glow Discharge Electrolysis (CGDE). In our experiments, we measure the temperature change of electrolyte and electrode as well as the change in current following on from the addition of, first, frozen and, second, boiling KOH aqueous solution (0.1 M). Quite surprisingly, only the addition of frozen KOH aqueous solution has a significant impact on current (+130%), caused by the decrease in electrolyte temperature (-11 degrees C). In contrast, the addition of boiling KOH aqueous solution has a negligible effect on current. A very similar behavior is recorded when frozen or boiling type III deionized water is used: the addition of ice has an even stronger impact on current (+145 %) and on electrolyte temperature (-14 degrees C), while adding boiling water has no measurable effect. Thus, we here demonstrated that electrolyte temperature is critical for managing the responsiveness of the CGDE system. Our results pave the way toward temperature controlled CGDE, a powerful tool for a greener and a more efficient environmental chemistry
Emerging strategies towards ambient condition fabrication of perovskite solar cells
No full textThe power conversion efficiency of perovskite solar cells (PSCs) has remarkably increased, in just a few years, from 3.8 to 22.7%, due to the excellent properties of organometal-halide perovskite, such as strong and broad optical absorption from visible to near infrared, high electron and hole diffusion length and a low surface recombination velocity. Nevertheless, PSCs are susceptible to oxygen and water, because of a degradation pathway leading to the formation of lead iodide, methylammonium and hydrogen iodide. For this reason, perovskite materials require high temperature and glove-box synthetic conditions, thus hindering large-scale applications. During last year, a few efforts have been made in the development of ambient condition fabrication strategies, such as thermal engineering and the use of anti-solvents. In the first case, the substrate TiO2 is pre-heated at low temperature before spin-coating deposition of perovskite precursors. This ensures phase purity and a pinhole-free morphology, with a PCE reaching 12%. In the second case, the use of anti-solvents reduces the solubility of perovskite precursors, thereby promoting fast nucleation and rapid crystallization. In this way, the effect of air-moisture is less relevant. In conclusion, the fabrication of PSCs in open air atmospheric conditions is challenging, but necessary for photovoltaic application of perovskite materials
Ambient condition fabrication of perovskite solar cells: towards industrial approaches
No full textThe power conversion efficiency of perovskite solar cells (PSCs) has remarkably increased, in just a few years, from 3.8 to 22.7%, due to the excellent properties of organometal-halide perovskite, such as strong and broad optical absorption form visible to near infrared, high electron and hole diffusion length and a low surface recombination velocity. Nevertheless, PSCs are susceptible to oxygen and water, because of a degradation pathway leading to the formation of lead iodide, methylammonium and hydrogen iodide. For this reason, perovskite materials require high temperature and glove-box synthetic conditions, thus hindering large-scale applications.
During last year, a few efforts have been made in the development of ambient condition fabrication strategies, such as thermal engineering and the use of anti-solvents. In the first case, the substrate TiO2 is pre-heated at low temperature before spin-coating deposition of perovskite precursors. This ensures phase purity and a pinhole-free morphology, with a PCE reaching 12%. In the second case, the use of anti-solvents reduces the solubility of perovskite precursors, thereby promoting fast nucleation and rapid crystallization. In this way, the effect of air-moisture is less relevant.
In conclusion, the fabrication of PSCs in open air atmospheric conditions is challenging, but necessary for photovoltaic application of perovskite materials (4)
Mesoporous materials and nanostructured LiFePO4 as cathodes for secondary Li-ion batteries: synthesis and characterisation
No full textEnergy, environmental concerns and information technology (IT) have become thrust areas for the 21st century, as they are closely linked to the technological development. The search for energy sources to provide comfort and a smooth lifestyle has taken place since the beginning of civilization; however, the present energy needs are very much dependent on nuclear and fossil fuel (oil). Currently, as the internal combustion engine is a major user of fossil fuel, consuming about 1/3 of the annual total demand for energy, concern over global warming and air pollution has become evident. Consequently, there is a high worldwide incentive to find more efficient, convenient, pollution-free and safe power sources; examples of advanced techniques include fuel cells and solar cells.
Reliable methods for storing energy are just as important and secondary lithium-ion batteries provide an attractive solution. The lithium-based battery technology of today out-performs many other conventional systems, such as the lead-acid, nickel-cadmium and nickel-metal hydride batteries, because of its high energy and power density, and design flexibility, in combination with the use of environmentally acceptable constituents. Li-ion battery is a compact, lightweight, rechargeable power source stable to over 500 cycles. It can be fabricated in size ranging from a few microns to a large-scale battery capable of providing power for computer memory chips, communication equipments, colour motion pictures and, potentially, for the huge market of electric vehicles (EV) and hybrid-electric vehicles (HEV), where low cost, low environmental impact, as well as high specific performance batteries are needed.
Li-based battery chemistry is, however, relatively young. Thus, the constant demand for higher energy density, thinner, lighter and even more mechanically flexible batteries has motivated research into new cell configurations and new battery chemistries and electrode materials.
The scope of this thesis is the development of new cathode materials for secondary Li-ion batteries and the assessment of their structural-morphological characteristics and electrochemical performance.
Chapter I deals with the basic concepts for cells and batteries and with a brief description of the history of the battery and of the general characteristics of the mature portable power-source technologies (i.e., lead-acid, Ni-Cd and Ni-MH).
Chapter II discusses the historical developments, present status and future trends in Li-based batteries research. Their characteristics, working principles and components are also discussed.
The energy density of lithium batteries has not increased in the last 20 years, and the specific capacity (Ah/kg) has actually decreased. Thus, much effort is being directed at finding new materials, both electrode materials and electrolytes, that can provide higher capacities, lower costs, and are environmentally benign. This is shown in Chapter III, that presents the materials and components relevant to the Li-ion battery technology during recent years and for the next future. The cathode is particularly critical in determining the capacity of a Li-based battery, as it is the heaviest component, and it has the greatest potential for improvement. For this component, further basic requirements for the potentially wide market of EVs and HEVs are the availability, low cost (high Wh/€) and low environmental impact, as well as high power capability.
The experimental part of this thesis deals with the research work carried out on ordered modified mesoporous materials and nano-structured phospho-olivine LiFePO4 as cathode materials for Li-ion cells. In Chapter IV the characterization techniques and methods used to analyse the synthesized samples, either from the structural-morphological or electrochemical point of view, are briefly described.
In Chapter V, the experimental results are shown regarding the three different strategies adopted in order to produce transition-metal containing mesoporous materials, suitable as cathodes for Li-ion cells. In this connection, the first attempt was to produce siliceous (MCM-41 type) and alumino-phosphate (AlPO-type) mesoporous materials, trying to substitute the largest amount of Si and/or Al with Mn ions, by direct hydrothermal synthesis. As their electrochemical results in Li cells were not satisfying, we synthesized mesoporous MCM-48 silica supported with transition-metal oxides (both MnO2 and Fe2O3) nanoparticles, by the wet impregnation technique. Finally, the experimental results are reported regarding the strategy adopted in order to support nanoparticles of FePO4, which is a well-known and extensively studied material for Li-ion batteries, into the channels of an ordered mesoporous SBA-15 silica.
Phospho-olivine lithium iron phosphate (LiFePO4) is a potential cathode material for the next generation of secondary Li-ion batteries, as it fulfils the requirements of high theoretical specific capacity, low toxicity, low cost and availability. In Chapter VI, the development of a new, easy and low cost hydrothermal synthetic route to produce high surface area and high performance nano-structured LiFePO4 powders is reported. The aim was to investigate the influence of the synthetic route and preparation conditions (presence of a surfactant during synthesis) on the chemical-physical properties of the LiFePO4/C composites and, as a consequence, on their electrochemical performances. CTAB has been chosen as the surfactant for its high dispersing activity. Moreover, during the firing step in inert atmosphere, CTAB favours the preparation and the homogeneity of the LiFePO4/C composites and the obtaining of a positive influence on their electrochemical performances
Advanced materials & green processes for a sustainable society (INSTM Sestriere 2022)
No full textThis virtual special issue gathers a selection of articles following contributions presented at the XIII INSTM Conference on Materials Science and Technology, the yearly event that gathers the national community, which was held at the Olympic Village TH Hotel in Sestriere (Torino, Italy), built for the 2006 Winter Games, with panoramic views toward one of the most famous Europe's skiing resorts on the mountains of the north-west side of Italy
Ambient condition fabrication of perovskite solar cells
No full textThe power conversion efficiency of perovskite solar cells (PSCs) has remarkably increased, in just a few years, from 3.8 to 22.7%, due to the excellent properties of organometal-halide perovskite, such as strong and broad optical absorption form visible to near infrared, high electron and hole diffusion length and a low surface recombination velocity. Nevertheless, PSCs are susceptible to oxygen and water, because of a degradation pathway leading to the formation of lead iodide, methylammonium and hydrogen iodide. For this reason, perovskite materials require high temperature and glove-box synthetic conditions, thus hindering large-scale applications.
During last year, a few efforts have been made in the development of ambient condition fabrication strategies, such as thermal engineering and the use of anti-solvents. In the first case, the substrate TiO2 is pre-heated at low temperature before spin-coating deposition of perovskite precursors. This ensures phase purity and a pinhole-free morphology, with a PCE reaching 12%. In the second case, the use of anti-solvents reduces the solubility of perovskite precursors, thereby promoting fast nucleation and rapid crystallization. In this way, the effect of air-moisture is less relevant.
In conclusion, the fabrication of PSCs in open air atmospheric conditions is challenging, but necessary for photovoltaic application of perovskite materials
UV-induced polymer electrolytes for all solid-state lithium batteries
No full textWe all desire a long-lasting, non-explosive, flexible and small lithium-ion battery (LIB) for our portable electronic devices and (future) electric vehicles. The use of a solid polymer as electrolyte, instead of a flammable solvent, is currently the most promising solution for thinner and safer LIBs. Poly(ethylene oxide)-based polymers (PEO) are widely used, even commercially, thanks to their good ability to transport lithium ions at temperatures over 60 °C.
In our Lab, we focus on the structuring of classic −EO− based backbones by photo-polymerization, a fast, cost-effective and solvent-free technique. Solid polymer electrolytes (SPEs) based on different monomers/oligomers are prepared. By incorporating high amounts of plasticizers and lithium salts, outstanding ionic conductivities are obtained (σ > 10–4 S cm–1 at 20 °C) along with wide electrochemical stability window (>5 V vs. Li+/Li) as well as good interfacial stability. Besides, SPEs have remarkable morphological characteristics in terms of homogeneity, flexibility and robustness.
All-solid lithium-based polymer cells show very good cycling behavior in terms of rate capability and stability over a wide range of operating temperatures, which confirms the promising prospects of photocured polymer electrolytes for practical application at ambient/sub-ambient temperatures
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