Supercapacitors on Flexible Substrates for Energy Autonomous Electronics

Electrical energy storage facilitates the use of electrical devices also when there is no full-time external energy source available. Electrical energy can be stored chemically as in batteries or in electric field as in capacitors. Supercapacitors are electrochemical cells in which energy is stored in electric field in the interface between electrode surface and electrolyte. Typically supercapacitors have higher power density but lower energy density than batteries. In general, supercapacitors have longer lifetime and they can be used in a wide temperature range.The goal of the research reported in this thesis was to study and develop small, flexible, environmentally friendly supercapacitors for e.g. Internet of Things or wireless sensor network applications, with emphasis on inexpensive materials. A second focus of the research was on scalable solution based processes which are similar to mass printing making large-scale production feasible. A further goal was to avoid toxic materials in order to enable disposable or incinerable devices.The supercapacitors were fabricated on paperboard or polymer substrates. Metal foils, silver ink and graphite ink were used as current collectors, activated carbon or polypyrrole as electrode material and paper as separator. Biopolymer chitosan was used as electrode binder and also demonstrated to work as a separator. In most experiments aqueous sodium chloride acted as electrolyte. Typically the area of the electrodes was 2 cm2. A monolithic structure facilitating supercapacitor fabrication by a solution process method was developed.The capacitance values of the supercapacitors were of the order of 0.1-0.5 F. Depending on the current collector material and dimensions, the equivalent series resistance ranged from below 1 to above 30 . Self-discharge properties for various types of supercapacitors were defined: still after 30 days over 50 % of the charged energy remained. Energy efficiency values were up to 96 %. These numerical values are adequate for energy storage components in practical application and thus show that the goals set for the research were reached

Fertilizer and soil conditioner value of broiler manure biochars

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A novel solution for utilizing liquid fractions from slow pyrolysis and hydrothermal carbonization - Acidification of animal slurry

Pyrolysis and hydrothermal carbonization (HTC) have recently gained much interest in the field of biomass processing. This is due to the process flexibility with respect to raw materials and the range of potential applications proposed for the end products. In addition to the main product, biochar, the processes yield a liquid fraction that has turned out to be challenging to productize. Considering the feasibility of the thermochemical conversion technologies, it is crucial that all the produced fractions can be utilized reasonably and no waste fractions expensive to dispose remain. In spite of active research and development work, unambiguous uses for the liquid fractions have not been recognized yet. Please click on the file below for full content of the abstract

Proaktiivisa toimijoita vai koekaniineita Euroopan tietoyhteiskuntalaboratoriossa? : Lipposen hallituksen tulevaisuusselonteon kommentointia tulevaisuudentutkimuksen näkökulmasta

Valtioneuvosto antoi eduskunnalle tulevaisuuselontekonsa kahdessa osassa: Syksyllä 1996 ilmestynyt Suomi ja Euroopan tulevaisuus tarkasteli Euroopan tulevaisuutta ja Suomen asemaa siinä. Keväällä 1997 annettu toinen osa Reilu ja rohkea - vastuun ja osaamisen Suomi oheisjulkaisuineen käsitteli erityisesti oman maamme kehityskulkuja, vaihtoehtoja ja strategisia valintoja. Tässä julkaisussa analysoidaan tulevaisuusselontekoa kriittisesti siltä pohjalta, vastaako se sille asetettuihin tavoitteisiin ja kuinka hyvin hallitus onnistui tehtävässään. Selonteossahan luvataan, että hallitus esittää linjauksensa Suomen tulevaisuuden ydinkysymyksiin. Artikkelissa esitetään kokonaisarvio selonteosta tulevaisuudentutkimuksen näkökulmasta. Kritiikin kohteina ovat toisaalta selonteon metodiset valinnat, aikajänne ja työskentelyprosessi siihen liittyvine ongelmineen ja toisaalta artikkelissa arvioidaan selonteossa esitettyä kokonaisnäkemystä Suomen valinnoista ja mahdollisuuksista sekä näiden taustalla vallitsevaa arvopohjaa

Bending reliability of screen-printed vias for a flexible energy module

The future of printed electronics involves advancements not only related to full system integration, but also lean process manufacturing. A critical aspect of this progress is developed in this study, which evaluates a highly flexible screen printed through-hole-via using silver microparticle inks, for applications in energy harvesting and storage modules. The printed vias’ fabrication and durability are evaluated by means of a double sided screen-printing method and repetitive (cyclic) bending tests. Vias, through 125-µm-thick PET foil, were laser cut (nominally 50, 100, 150, and 200 µm diameters) then filled, and simultaneously connected to adjacent vias by screen printing. To investigate the use of the printed via in a monolithic energy module, the vias were used for the fabrication of a flexible printed supercapacitor containing aqueous electrolyte and carbon electrodes. The results indicate that the lower viscosity silver ink (DuPont 5064H) fills the via less effectively than the higher viscosity ink (Asahi LS411AW), and as the via size increases (≥150 µm diameter) via walls are coated rather than filled. Conversely, the more viscous ink fills the via thoroughly and exhibited a 100% yield (1010 vias; 100 µm nominal via diameter) with the two-step direct screen-printing method. The 10-mm radius bending test showed no signs of via specific breakdown after 30,000 cycles. The results indicate that this via filling process is likely roll-to-roll compatible to enable multi-layered printed electronic devices.publishedVersionPeer reviewe

Reliability test of fully printed and flexible organic electrolyte-based supercapacitor

As the demand for supercapacitors in various flexible and wearable energy sectors grows, reliability becomes a key aspect to consider. We report the fabrication and reliability study of printed, flexible organic electrolyte-based supercapacitors. The supercapacitor can be operated over a wide temperature range from −40 ◦C to 100 ◦C with excellent repeatability and stability. Thermal shock tests led to a defect in the electrode layer’s microstructure, which reduces the supercapacitor performance. Cyclic bending experiments show that the device has excellent robustness, mechanical flexibility, long-term electrical stability, and 100% capacitance retention up to 10 000bending cycles with a bending radius of 0.41 cm. Thus, the device is suitable for wearable and flexible energy storage applications over a wide temperature range.Peer reviewe

Are there environmental or agricultural benefits in using forest residue biochar in boreal agricultural clay soil?

Short-term agronomic and environmental benefits are fundamental factors in encouraging farmers to use biochar on a broad scale. The short-term impacts of forest residue biochar (BC) on the productivity and carbon (C) storage of arable boreal clay soil were studied in a field experiment. In addition, rain simulations and aggregate stability tests were carried out to investigate the potential of BC to reduce nutrient export to surface waters. A BC addition of 30 t ha−1 increased soil test phosphorus and decreased bulk density in the surface soil but did not significantly change pH or water retention properties, and most importantly, did not increase the yield. There were no changes in the bacterial or fungal communities, or biomasses. Soil basal respiration was higher in BC-amended plots in the spring, but no differences in respiration rates were detected in the fall two years after the application. Rain simulation experiments did not support the use of BC in reducing erosion or the export of nutrients from the field. Of the C added, on average 80% was discovered in the 0–45 cm soil layer one year after the application. Amendment of boreal clay soil with a high rate of BC characterized by a moderately alkaline pH, low surface functionalities, and a recalcitrant nature, did not induce such positive impacts that would unambiguously motivate farmers to invest in BC. BC use seems unviable from the farmer's perspective but could play a role in climate change mitigation, as it will likely serve as long-term C storage.202

Simplified exponential equivalent circuit models for prediction of printed supercapacitor's discharge behavior - Simulations and experiments

Although supercapacitors (SCs) are promising devices for energy storage systems due to their high-power density and long lifecycle, they suffer from high leakage current and self-discharge. In this work, a simple and practical exponential equivalent circuit model (ECM) and three sub-ECMs based on electrical parameters and self-discharge profile of 12 printed flexible SCs are proposed to account for non-linear leakage and self-discharge phenomena in SCs. The capacitance and equivalent series resistance (ESR) of SCs are determined from the experiments. Besides, rather than modelling different self-discharge mechanisms within a SC cell, an exponential current/voltage function is employed for each SC in this study as a variable leakage resistance (VLR). The proposed ECMs are based on empirical parameters, without considering the physical mechanisms. Using the ECMs and only knowing two to four parameters for each SC cell, the discharge behaviors of SCs, electrochemical double-layer capacitors (EDLCs) type may be predicted with a high degree of accuracy over the long term (maximum simulation error in 31 days: less than 4%). Accordingly, the proposed ECMs, in contrast to those published in the literature, have the potential to be used in practical applications in the long-term as a result of their simplicity and high accuracy.publishedVersionPeer reviewe

A Modified Exponential Equivalent Parallel Resistance (EPR) Model for Predicting Self-Discharge Behavior of Printed Flexible Supercapacitors

Typically, batteries are used to power interconnected Internet of Things (IoT) devices. Intermittent manual replacement of batteries or recharging them after complete depletion is one of their major disadvantages, which increases the cost of maintaining and restricts the large-scale use of devices. Considering the longevity of devices and battery limitations, and in order to achieve the integrated and efficient operation of IoT devices, the development of alternative power sources and power management strategies is inevitable. The supercapacitor is a suitable energy storage option for energy-harvesting powered autonomous wireless sensor nodes in IoT applications. The leakage current value provided for the supercapacitors by the manufacturers is tested after the supercapacitor has been floated at a constant voltage for a long time. This raises concerns about the uncertainty of dynamic leakage current behavior during repeated charging and discharging of the supercapacitor in IoT applications. At present, there is no effective method to estimate and predict leakage current and the discharging behavior of supercapacitors in IoT applications with the aim of achieving optimal performance. In this work, an improved simplified exponential model is presented in order to simulate the non-linear discharge behavior of our fabricated printed flexible supercapacitors in long-term (31 days). The printed supercapacitors are disposable and have been fabricated using low-cost and non-toxic processes and materials. The model proposed in this work is very well adapted to the experimentally measured self-discharge results of the supercapacitors. In addition, according to the experimental and data fitting results of 10 fabricated supercapacitors, all the parameters defined in this model show good statistical values and have a Gaussian (normal) distribution.acceptedVersionPeer reviewe