Elaboration of flexible lithium - ion electrodes by printing process

The work presented in this manuscript describes the manufacturing of lithium-ion batteries on papers substrates by printing technique. Its aim is the development of new up scalable and large area techniques as screen printing for the fabrication of lithium-ion batteries and the replacement of conventional toxic components by bio-sourced one and water based solvent. First results shows how it is possible to formulate cellulose based ink tailored for screen printing technology with suitable properties for lithium-ion batteries requirements. Electrodes were manufactured and tested from a physical and electrochemical point of view and two strategies were proposed to enhance performances. Finally, by considering results obtained for the electrodes, a full cell was manufactured with a new assembling strategy based on: front / reverse printing approach and the embedding of the current collectors during printing stage. As a final point cells were characterized and compared with others obtained by conventional assembling strategies.Le travail présenté dans ce mémoire concerne la réalisation des batteries souples lithium-ion. Il a comme objectif le développement de nouveaux procédés comme l'impression par sérigraphie pour la fabrication de batteries et le remplacement des polymères issus de la chimie de synthèse par des matériaux bio-sourcés utilisables en milieu aqueux. Les résultats obtenus ont montré qu'il est possible de formuler des encres aqueuses à base des matériaux actifs classiquement utilisés pour l'élaboration d'électrodes (anode et cathode) de batterie Li-ion mais avec des liants dérivés de cellulose en substitution du PVDF qui intègre les formulations standards. Cette encre, dont les propriétés rhéologiques sont compatibles avec le procédé d'impression sérigraphique, permet l'obtention d'électrodes présentant des propriétés spécifiques aux bons fonctionnements de la batterie. Les résultats obtenus ont montré que cette technique d'impression du séparateur pouvait être utilisée pour remplacer la technique de déposition classique des matières actives sur les collecteurs de courant, basée sur un procédé d'enduction à lame (blade coating). Enfin, une batterie lithium-ion imprimée a pu être élaborée en utilisant la stratégie d'impression recto/verso du séparateur avec l'intégration des collecteurs de courant pendant la phase d'impression, validant ainsi cette nouvelle technique d'assemblage

A Study On Mechanical And Electrical Properties Of Hybridized Graphene-Carbon Nanotube Filled Conductive Ink

Many researchers are now competing to fabricate an electronic device to meet the technological demand by using new conductive materials. There are several varieties of conductive inks on the market and it is crucial to choose the right ink fitting in the electronic applications. Conductive ink is a special type of ink that allows an electric current to flow through the ink. The conductive ink-filled epoxy is also known as conductive composites because the ink itself is based on more two ingredients such as filler, binder, and hardener. As interconnect material, the conductive inks should feature good electrical, mechanical and thermal properties. Nonetheless, to-date, there are some issues with current conductive ink that available in the market namely printing quality, high electrical resistivity as well as inferior mechanical strength. Therefore, this study aims to produce highly functional conductive ink using two types of carbon-based conductive fillers with epoxy as a binder. More specifically, graphene nanoplatelets (GNP) and multiwalled carbon nanotube (MWCNT) were used to produce the hybrid conductive ink. As a baseline, both fillers, GNP and MWCNT with epoxy were formulated separately using a minimum percentage at the beginning and the amount of filler was increased based on the conductivity level required. The percentage of filler for GNP was varied from 10-35 wt.% while for MWCNT for by 3- 8 wt.%. It is very important to make sure the materials are in contact with each other and therefore the movement of an electron will become easier. Following this, the hybridization of these two materials was made to produce conductive ink with enhanced functionality. The fabrication of the ink was carried out by using a direct mixing method starting from the formulation of the ink, mixing process, printing process and curing process to produce highly conductive hybridized ink. This research also studies the effect of the temperature on electrical, mechanical properties and surface roughness of the hybrid conductive ink using a varying amount of filler for both GNP and MWCNT inks. The electrical properties and the mechanical properties were assessed using a Four-point probe by following the ASTM F390 and a Dynamic Ultra Microhardness using ASTM E2546-15 as a guideline. The experimental results demonstrate an improvement in electrical conductivity. GNP showed higher resistivity around 38 kohm/sq whereas MWCNT showed much lower resistivity around 3.3 kohm/sq. When the hybridization occurs, the result obtained somewhat lower than MWCNT about 2.9 kohm/sq possibly due to the synergistic effect between the GNP and MWCNT, with better distribution and tunneling of electrons between both carbon-based conductive fillers. For mechanical properties, the hardness of hybrid ink is lower hence high in elastic modulus compared to GNP and MWCNT due to local stress concentration in the matrix. Furthermore, the surface roughness of hybrid resulted a smooth surface with the value of 0.833 µm compared to individual fillers. Smooth surface allow continuous conductive line formation without shorting risk

Effect of photonic flash annealing with subsequent compression rolling on the topography, microstructure and electrical performance of carbon-based inks

Binders used in screen-printed carbon-based inks are typically non-conductive. Photonic annealing and subsequent compression rolling have therefore been employed to remove binder and consolidate the conductive particles. Using this method, screen-printable carbon inks containing graphite only, graphite nanoplatelets and a combination of graphite and carbon black were assessed. Photonic annealing leads to the degradation of the polymer binder separating the carbon morphologies, with subsequent compression rolling leading to significant reductions in print film thickness, roughness and improvements in particle orientation. Both processes lead to electrical performance enhancement for all printed inks assessed. The process was most effective for single graphitic morphologies with large gaps between conductors. These saw significant improvements, with reductions in electrical resistivity from 1.91 to 0.23 Ω cm for the graphite ink. The mixed carbon ink saw smaller but still significant improvements in print roughness and resistivity, from 0.037 to 0.019 Ω cm. Therefore, these postprocesses could widen the applications of common, low-cost carbon morphologies in screen printing inks

Effect of the different printing patterns of graphene nanoparticles in conductive ink on electrical and mechanical performance

The utilization of graphene in the formation of conductive ink has been positively accepted by the electronics industry especially with the emerging of printable and flexible electronics. Because of that, it motivates this study to investigate the electrical, mechanical, and morphological properties for different patterns of Graphene Nanoparticle (GNP) conductive ink. The samples were prepared using the screen-printing technique with a low annealing temperature of 100 ºC for 30 minutes. The investigated parameter for the electrical property was the sheet resistivity, which showed that the zigzag pattern recorded the highest value of 1.077 kΩ/sq at the 3 mm of ink thickness. For the mechanical properties, the highest of hardness for 2 mm thickness was the curve pattern and for 3 mm was the square pattern, with the values of 3.849 GPa and 4.913 GPa. Both maximum values showed a direct correlation with the behavior of the elastic modulus of the ink. The maximum values of elastic modulus were recorded at the same ink pattern and thickness. For the morphological analysis, the surface roughness and qualitative analysis using SEM images were performed. The surface roughness showed that the increase of GNP in the composition increased the surface roughness because it decreased the homogeneity of the mixture. The recorded SEM images of the ink layer microstructure surface showed a direct correlation with the obtained sheet resistivity data. The samples that produced high sheet resistivity showed the presence of bumps, creases, and defects on the ink layer surface. Based on the obtained data, the correlation between electrical, mechanical, and morphological properties can be established for the GNP conductive ink with various patterns and thicknesses

Coating of Conducting Polymers on Natural Cellulosic Fibers

The process of combining natural cellulosic fibers with conducting polymers (CPs) is being pursued by scientist and researchers for their achievable synergistic electrical and biofriendly properties. CPs can be deposited on to a wide variety of cellulosic substrate and fibers, thus achieving good interactions between them. Various methods of deposition include in situ polymerization, physical coating, multilayering, and printing. Such materials are used for achieving more sustainable and low-cost CP-based applications

Flexible thin films on textiles for solar cells

In recent years, there has been an increase in studies about developing photovoltaic fabrics which can be used in different textile and clothing applications. The flexibility of the solar cells could be useful in many applications, for example providing power for small portable electronic devices such as personal digital assistants or on a larger scale for sunshades and canopies. In this work, we have taken the direct approach to deposit amorphous silicon cells directly onto fabrics. To achieve that, we have studied approaches to obtaining flexible conductive surfaces on polyester fabrics by using a double layer of metal and commercially available conductive polymer. Then both single and stacked metal contact layers and thin amorphous silicon films were built on glass and flexible substrates for optical and electric characterisation. It was shown by bending tests that the conductive fabrics retain both flexibility and electrical conductivity. Finally, complete n-i-p single junction a-Si:H cells were fabricated on different types of substrates such as glasses, polyester fabric and polytetrafluoroethylene fabric (PTFE). Several challenging aspects related to the fabrication and characterisation of solar cells on fabrics are highlighted. Cells on woven fabrics were shown to be active photovoltaic devices though with lower response than equivalent cells on rigid glass substrates

Investigation of Electrolyte Wetting in Lithium Ion Batteries: Effects of Electrode Pore Structures and Solution

Beside natural source energy carriers such as petroleum, coal and natural gas, the lithium ion battery is a promising man-made energy carrier for the future. This is a similar process evolved from horse-powered era to engine driven age. There are still a lot of challenges ahead like low energy density, low rate performance, aging problems, high cost and safety etc. In lithium ion batteries, investigation about manufacturing process is as important as the development of material. The manufacturing of lithium ion battery, including production process (slurry making, coating, drying etc.), and post-production (slitting, calendering etc.) is also complicated and critical to the overall performance of the battery. It includes matching the capacity of anode and cathode materials, trial-and-error investigation of thickness, porosity, active material and additive loading, detailed microscopic models to understand, optimize, and design these systems by changing one or a few parameters at a time. In the manufacturing, one of the most important principles is to ensure good wetting properties between porous solid electrodes and liquid electrolyte. Besides the material surface properties, it is the process of electrolyte transporting to fill the pores in the electrode after injection is less noticed in academic, where only 2-3 drops of electrolyte are needed for lab coin cell level. In industry, the importance of electrolyte transport is well known and it is considered as part of electrolyte wetting (or initial wetting in some situations). In consideration of practical usage term, electrolyte wetting is adopted to use in this dissertation for electrolyte transporting process, although the surface chemistry about wetting is not covered. An in-depth investigation about electrolyte wetting is still missing, although it has significant effects in manufacturing. The electrolyte wetting is determined by properties of electrolyte and electrode microstructure. Currently, only viscosity and surface tension of electrolyte is used to reflect performance of electrolyte wetting. There are very few reports about quantitative measurement about electrolyte wetting. Moreover, there are only simple qualitative observations, good, poor, and fair, were reported on the wettability of microporous separators. Therefore, development of a quantitative analysis method is critical to help understand the mechanism of how electrolyte wetting is affected by material properties and manufacturing processes. In this dissertation, a quantitative test method is developed to analyze the electrolyte wetting performance. Wetting rate, measured by wetting balance method, is used to quantitatively measure the speed of electrolyte wetting. The feasibility of the wetting rate is demonstrated by repeated test of wetting rate between electrolytes and electrodes. Various electrolytes from single solvents to complicated industrial level electrolytes are measured with baseline electrodes. Electrodes with different composition, active materials and manufacturing process, separator sheets with different materials and additives are also measured with baseline electrolyte. The wetting behaviors for different materials and manufacturing processes could be used to help improve the optimization of production process. It is very necessary to reveal the mechanism underlying electrolyte wetting, especially the effects of electrode pore microstructure. The Electrodes, which are composed of active material, binder and carbon black, are formed by production process (rheological processing, coating, drying), and post-production process (calendaring and slicing etc.). The pore structure is also complicated by the broad size range of pores from nanometer to tens micrometer. In this dissertation, a pore network concept, as revealed in the MIP test (mercury intrusion porosimetry), is employed to characterize the electrode pore structure. It is composed by the random pore cavity and connected part of pores, which are further described by the percentage of total pore volume and the threshold and critical pore diameter. The effect of calendering process on electrolyte wetting, as a demonstration for typical post-production process, has been revealed by the wetting balance analysis. A quantitative analysis of the pore structure under the pore network concept is used to investigate the evolution of pore structure with the increase of calendering force. Based on the pore structure, the hypothesis of combined effects of capillary and converging-diverging flow in electrolyte wetting is proposed to understand the mechanism. A further demonstration of the effect of production process by adding excessive carbon black is accomplished. The hypothesis is valid to explain the electrolyte wetting behavior with increasing amount of carbon black. The pore structure differences between electrodes with various amount of carbon black are shown by the scanning electron microscope

Advanced Manufacture by Screen Printing

Screen-printing is the most widely used process in printed electronics, due to its ability to transfer materials with a wide range of functional properties at high thickness and solid loading. However, the science of screen printing is still rooted in the graphics era, with limited understanding of the fundamental science behind the ink transfer process. A multifaceted approach encompassing all aspects of the production of printed electronics from ink formulation, through screen-printing and post processing was therefore undertaken. With a focus on carbon inks due to their electrical conductivity, low cost, inertness and ability to be modified or functionalised. Parametric studies found that with blade squeegees, lower angles and softer blades led to increases in ink deposition, irrespective of ink rheology. However, the effects of print speed and snap distance were related to the rheology of the inks. Existing computational models were inaccurate and based on two contrasting theories. Extensional CaBER testing provided qualitative indications of the effect of separation speed and distance on deposition. However, this could only assess the effect of vertical, 2-dimensional forces and could not evaluate the influence of shear forces due to separation angle or the effects of the screen mesh. For this purpose, a screen-printing visualisation rig was specifically constructed, allowing the ink transfer mechanism to be captured for the first time. This identified similarities with one of the two theories, although existing models had oversimplified the process and did not account for variations in lengths of the separation regions or the contact angle between the mesh and substrate. It was also found that changes in the ink rheology and parameter settings changes the lengths of these regions, as well as the shape and presence of filaments formed during separation. The parameters of print speed, snap distance, solid loading and ink rheology were assessed and found to affect the mesh/substrate contact time and filamentation behaviour. This had a quantifiable effect on ink deposition, in terms of the amount of ink transfer, roughness and therefore conductivity. Finally, photonic annealing and subsequent compression rolling were found to enhance the conductivity of carbon inks by removing binder between particles and consolidating the ink film, leading to 8 times reduction in resistivity for a graphite-based ink and halving in resistivity for an ink containing a combination of carbon black and graphite, where there was less potential for improvement due to the conductive bridges between the graphite flakes

Printed and drawn flexible electronics based on cellulose nanocomposites

Sustainability, flexibility, and low-power consumption are key features to meet the growing re- quirements of simplicity and multifunctionality of low-cost, disposable/recyclable smart electronic -of- -based composites hold po- tential to fulfill such demands when explored as substrate and/or electrolyte-gate, or as active channel layer on printed transistors and integrated circuits based on ionic responses (iontronics). In this work, a new generation of reusable, healable and recyclable regenerated cellulose hydro- gels with high ionic conductivity and conformability, capable of being provided in the form of stick- ers, are demonstrated. These hydrogels are obtained from a simple, fast, low-cost, and environ- mental-friendly aqueous alkali salt/urea dissolution method of native cellulose, combined with eration and simultaneous ion incorporation with acetic acid. Their electrochemical properties can be also merged with the mechanical robustness, thermal resistance, transparency, and smooth- - strate. Beyond gate dielectrics, a water-based screen-printable ink, composed of CMC binder and com- mercial zinc oxide (ZnO) semiconducting nanoparticles, was formulated. The ink enables the printing of relatively smooth and densely packed films on office paper with semiconducting func- tionality at room temperature. The rather use of porous ZnO nanoplates is beneficial to form per- colative pathways at lower contents of functional material, at the cost of rougher surfaces. The engineered cellulose composites are successfully integrated into flexible, recyclable, low- voltage (<3.5 V), printed electrolyte-gated office paper or on the ionically modified nanopaper. Ubiquitous calligraphy accessories are used -the- out on the target substrate, where are already printed the devices. Such concept paves the way for a worldwide boom of creativity, where we can freely create personal electronic kits, while having fun at it and without generating waste.Sustentabilidade, flexibilidade e baixo consumo energético são características chave para atender aos crescentes requisitos de simplicidade e multifuncionalidade de sistemas eletrónicos inteligentes de baixo custo, das- Compósitos à base de celulose têm potencial para atender a tais necessidades quando explora- dos como substrato e/ou porta-de-eletrólito ou como camada de canal ativo em transístores impressos e circuitos integrados baseados em respostas iónicas (iontronics). Neste trabalho, é demonstrada uma nova geração de hidrogéis reutilizáveis, reparáveis e recicláveis baseados em celulose regenerada, que apresentam alta condução iónica e conformabilidade, podendo ser fornecidos na forma de adesivos. Estes hidrogéis são obtidos a partir de um método simples, rápido, barato e amigo do ambiente que permite a dissolução de celulose nativa em soluções aquosas com mistura de sal alcalino e ureia, combinado com carboximetil celulose (CMC) para melhorar a sua robustez, seguido da regeneração e simultâneo enriquecimento iónico com ácido acético. As suas propriedades eletroquímicas podem ser combinadas com a inbase de celulose micro/nanofibrilada para obter um substrato eletrolítico semelhante a papel. Para além de portas-dielétricas, foi formulada uma tinta aquosa compatível com serigrafia, composta por CMC como espessante e nanopartículas semicondutoras de ZnO. A tinta permite a impressão de filmes pouco rugosos e densamente percolados sobre papel de escritório, e com funcionalidade semicondutora à temperatura ambiente. O uso alternativo de nanoplacas porosas de ZnO é benéfico para criar caminhos percolativos com menores teores de material funcional, apesar de se obter filmes rugosos. Os compósitos à base celulose foram integrados com sucesso em transístores e portas lógicas porta-eletrolítica, os quais foram impressos em papel de escritório ou no "nanopapel" iconicamente modificado. Acessórios de caligrafia permitem a fácil e rápida padronização de pistas condutoras/resistivas, desenhando-as no substrato alvo, onde estão impressos os dispositivos. Este conceito despoleta um mundo criativo, onde é possível criar livremente kits eletrónicos customizados de forma divertida e sem gerar resíduos