| 1. |
- Carlsson, Daniel O
(författare)
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Structural and Electrochemical Properties of Functionalized Nanocellulose Materials and Their Biocompatibility
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanocellulose has received considerable interest during the last decade because it is renewable and biodegradable, and has excellent mechanical properties, nanoscale dimensions and wide functionalization possibilities. It is considered to be a unique and versatile platform on which new functional materials can be based.This thesis focuses on nanocellulose from wood (NFC) and from Cladophora algae (CNC), functionalized with surface charges or coated with the conducting polymer polypyrrole (PPy), aiming to study the influence of synthesis processes on structural and electrochemical properties of such materials and assess their biocompatibility.The most important results of the work demonstrated that 1) CNC was oxidized to the same extent using electrochemical TEMPO-mediated oxidation as with conventional TEMPO processes, which may facilitate easier reuse of the reaction medium; 2) NFC and CNC films with or without surface charges were non-cytotoxic as assessed by indirect in vitro testing. Anionic TEMPO-CNC films promoted fibroblast adhesion and proliferation in direct in vitro cytocompatibility testing, possibly due to its aligned fibril structure; 3) Rinsing of PPy-coated nanocellulose fibrils, which after drying into free-standing porous composites are applicable for energy storage and electrochemically controlled ion extraction, significantly degraded the PPy coating, unless acidic rinsing was employed. Only minor degradation was observed during long-term ambient storage; 4) Variations in the drying method as well as type and amount of nanocellulose offered ways of tailoring the porosities of nanocellulose/PPy composites between 30% and 98%, with increments of ~10%. Supercritical CO2-drying generated composites with the largest specific surface area yet reported for nanocellulose/conducting polymer composites (246 m2/g). The electrochemical oxidation rate was found to be controlled by the composite porosity; 5) In blood compatibility assessments for potential hemodialysis applications, heparinization of CNC/PPy composites was required to obtain thrombogenic properties comparable to commercial hemodialysis membranes. The pro-inflammatory characteristics of non-heparinized and heparinized composites were, to some extent, superior to commercial membranes. The heparin coating did not affect the solute extraction capacity of the composite.The presented results are deemed to be useful for tuning the properties of systems based on the studied materials in e.g. energy storage, ion exchange and biomaterial applications.
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| 2. |
- Ciosek Högström, Katarzyna
(författare)
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The Complex Nature of the Electrode/Electrolyte Interfaces in Li-ion Batteries : Towards Understanding the Role of Electrolytes and Additives Using Photoelectron Spectroscopy
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The stability of electrode/electrolyte interfaces in Li-ion batteries is crucial to the performance, lifetime and safety of the entire battery system. In this work, interface processes have been studied in LiFePO4/graphite Li-ion battery cells. The first part has focused on improving photoelectron spectroscopy (PES) methodology for making post-mortem battery analyses. Exposure of cycled electrodes to air was shown to influence the surface chemistry of the graphite. A combination of synchrotron and in-house PES has facilitated non-destructive interface depth profiling from the outermost surfaces into the electrode bulk. A better understanding of the chemistry taking place at the anode and cathode interfaces has been achieved. The solid electrolyte interphase (SEI) on a graphite anode was found to be thicker and more inhomogeneous than films formed on cathodes. Dynamic changes in the SEI on cycling and accumulation of lithium close to the carbon surface have been observed. Two electrolyte additives have also been studied: a film-forming additive propargyl methanesulfonate (PMS) and a flame retardant triphenyl phosphate (TPP). A detailed study was made at ambient and elevated temperature (21 and 60 °C) of interface aging for anodes and cathodes cycled with and without the PMS additive. PMS improved cell capacity retention at both temperatures. Higher SEI stability, relatively constant thickness and lower loss of cyclable lithium are suggested as the main reasons for better cell performance. PMS was also shown to influence the chemical composition on the cathode surface.The TPP flame retardant was shown to be unsuitable for high power applications. Low TPP concentrations had only a minor impact on electrolyte flammability, while larger amounts led to a significant increase in cell polarization. TPP was also shown to influence the interface chemistry at both electrodes.Although the additives studied here may not be the final solution for improved lifetime and safety of commercial batteries, increased understanding has been achieved of the degradation mechanisms in Li-ion cells. A better understanding of interface processes is of vital importance for the future development of safer and more reliable Li-ion batteries.
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| 3. |
- Tammela, Petter, 1986-
(författare)
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On the electrochemical performance of energy storage devices composed of cellulose and conducting polymers
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Applications that require electrical energy storage are becoming increasingly diverse. This development is caused by a number of factors, such as an increasing global energy demand, the advent of electric vehicles, the utilization of intermittent renewable energy sources, and advances in disposable and organic electronics. These applications will set different demands on their electrical energy storage and, thus, there will be no single technology used for all applications. For some applications the choice of energy storage materials will be extremely important. Conventional batteries and supercapacitors rely on the use of nonrenewable inorganic materials mined from depleting ores, hence, requiring large amounts of energy for their processing. Such materials also add a significant cost to the final product, making them less attractive for large scale applications. Conducting polymers, on the other hand, constitute a class of materials that can be used for organic matter based energy storage devices.The aim of this thesis was to investigate the use of a composite consisting of the conducting polymer polypyrrole (PPy) and cellulose derived from Cladophora sp. algae for electrical energy storage. The polymer was coated onto the cellulose fibers by chemical polymerization resulting in a flexible material with high surface area. By using this composite as electrodes, electrochemical cells consisting of disposable and non-toxic materials can be assembled and used as energy storage devices. The resistances of these prototype cells were found to be dominated by the resistance of the current collectors and to scale with the thickness of the separator, and can hence be reduced by cell design. By addition of nanostructured PPy, the weight ratio of PPy in the composite could be increased, and the cell voltages could be enhanced by using a carbonized negative electrode. Composites of cellulose and poly(3,4-ethylenedioxythiophene) could also be synthesized and used as electrode materials. The porosities of the electrodes were controlled by mechanical compression of the composite or by coating of surface modified cellulose fibers with additional PPy. Finally, the self-discharge was studied extensively. It was found that oxygen was responsible for the oxidation of the negative electrode, while the rate of self-discharge of the positive electrode increases with increasing potential. Through measurements of the charge prior to and after self-discharge, as well as with an electrochemical quartz crystal microbalance, it was found that the self-discharge of the positive electrode was linked to an exchange of the counter ions by hydroxide ions. It is also demonstrated that the self-discharge rate of a symmetric PPy based device can be decreased dramatically by proper balancing of the electrode capacities and by reducing the oxygen concentration. The results of this work are expected to contribute towards future industrial implementation of electric energy storage devices based on organic materials.
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| 4. |
- Eriksson, Rickard
(författare)
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Structural Changes in Lithium Battery Materials Induced by Aging or Usage
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Li-ion batteries have a huge potential for use in electrification of the transportation sector. The major challenge to be met is the limited energy storage capacity of the battery pack: both the amount of energy which can be stored within the space available in the vehicle (defining its range), and the aging of the individual battery cells (determining how long a whole pack can deliver sufficient energy and power to drive the vehicle). This thesis aims to increase our knowledge and understanding of structural changes induced by aging and usage of the Li-ion battery materials involved.Aging processes have been studied in commercial-size Li-ion cells with two different chemistries. LiFePO4/graphite cells were aged under different conditions, and thereafter examined at different points along the electrodes by post mortem characterisation using SEM, XPS, XRD and electrochemical characterization in half-cells. The results revealed large differences in degradation behaviour under different aging conditions and in different regions of the same cell. The aging of LiMn2O4-LiCoO2/Li4Ti5O12 cells was studied under two different aging conditions. Post mortem analysis revealed a high degree of Mn/Co mixing within individual particles of the LiMn2O4-LiCoO2 composite electrode.Structural changes induced by lithium insertion were studied in two negative electrode materials: in Li0.5Ni0.25TiOPO4 using in situ XRD, and in Ni0.5TiOPO4 using EXAFS, XANES and HAXPES. It was shown that Li0.5Ni0.25TiOPO4 lost most of its long-range-order during lithiation, and that both Ni and Ti were involved in the charge compensation mechanism during lithiation/delithiation of Ni0.5TiOPO4, with small clusters of metal-like Ni forming during lithiation.Finally, in situ XRD studies were also made of the reaction pathways to form LiFeSO4F from two sets of reactants: either FeSO4·H2O and LiF, or Li2SO4 and FeF2. During the heat treatment, Li2SO4 and FeF2 react to form FeSO4·H2O and LiF in a first step. In a second step LiFeSO4F is formed. This underlines the importance of the structural similarities between LiFeSO4F and FeSO4·H2O in the formation process of LiFeSO4F.
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| 5. |
- Nyström, Gustav
(författare)
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Nanocellulose and Polypyrrole Composites for Electrical Energy Storage
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To meet the predicted increase in demand for energy storage in tomorrow's society, the development of inexpensive, flexible, lightweight and sustainable energy-storage materials is essential. In this respect, devices based on electroactive organic molecules, such as conducting polymers, are highly interesting. The aim of this thesis was to evaluate the use of nanocellulose as a matrix material in composites of cellulose and the electroactive polymer polypyrrole (PPy), and the use of these composites in all-polymer paper-based energy-storage devices. Pyrrole was polymerized using FeCl3 onto cellulose nanofibers in the form of a hydrogel. The resulting PPy-coated fibers were washed with water and dried into a high surface area, conductive paper material. Variations in the drying technique provided a way of controlling the porosity and the surface area of wood-based cellulose nanofibers, as the properties of the cellulose were found to have a large influence on the composite structure. Different nanocellulose fibers, of algal and wood origin, were evaluated as the reinforcing phase in the conductive composites. These materials had conductivities of 1–6 S/cm and specific surface areas of up to 246 m2/g at PPy weight fractions around 67%. Symmetrical supercapacitor devices with algae-based nanocellulose-PPy electrodes and an aqueous electrolyte showed specific charge capacities of around 15 mAh/g and specific capacitances of around 35 F/g, normalized with respect to the dry electrode weight. Potentiostatic charging of the devices was suggested as a way to make use of the rapid oxidation and reduction processes in these materials, thus minimizing the charging time and the effect of the IR drop in the device, and ensuring charging to the right potential. Repeated charging and discharging of the devices revealed a 10–20% loss in capacity over 10 000 cycles. Upon up-scaling of the devices, it was found that an improved cell design giving a lower cell resistance was needed in order to maintain high charge and discharge rates. The main advantages of the presented concept of nanocellulose-PPy-based electrical energy storage include the eco-friendly raw materials, an up-scalable and potentially cost-effective production process, safe operation, and the controllable porosity and moldability offered by the nanocellulose fiber matrix. Integrating energy storage devices into paper could lead to un- precedented opportunities for new types of consumer electronics. Future research efforts should be directed at increasing the energy density and improving the stability of this type of device as well as advancing the fundamental understanding of the current limitations of these properties.
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| 6. |
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| 7. |
- Rehnlund, David, 1986-
(författare)
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Insights into Electrochemical Energy Storage by use of Nanostructured Electrodes
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Template-assisted electrodeposition is a powerful technique for fabricating complex nanostructured electrodes. Through the use of pulsed-electrodeposition nanostructured electrodes of Al, Cu and Sn have been realised and subsequently coated electrochemically with V2O5, MnxO, Li, Cu2O and a polymer electrolyte. Nanorods with a multi-layered Cu2O/Cu structure have likewise been produced through electrodeposition. Nanostructured electrodes are ideal for studying electrochemical energy storage and have as such been used to investigate the electrochemistry of conversion and alloying reactions in detail.Key properties of the Cu2O conversion reaction were found to be dependent on the particle size. Prolonged cycling was seen to induce an electrochemical milling process which reduced the particle size. This process was found to improve the cell capacity retention due to improved accessibility of the material. The redox potential at which the particles react was found to be size dependent as smaller particles reacted at lower potentials.The Li-alloying reaction was also investigated by analysing several different alloy-forming materials. All materials exhibited a decline in capacity during cell cycling. This decline was observed to be time dependent and could as such be explained by a diffusion limited process. Moreover, the capacity losses were found to occur during partial lithiation of the electrode material leading to Li trapping in the electrode material. Li trapping was also observed for commonly used anode current collectors as the metals have some solubility for Li. Conducting boron-doped diamond electrodes were however seen to be resistant to Li diffusion and are therefore recommended as viable current collectors for anodes handling metallic lithium (i.e. Li-alloys and Li metal).
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| 8. |
- Bengtsson, Katarina
(författare)
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Additive manufacturing methods and materials for electrokinetic systems
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fabrication of miniaturized devices is usually time-consuming, costly, and the materials commonly used limit the structures that are possible to create. The techniques most often used to make microsystems involve multiple steps, where each step takes considerable time, and if only a few systems are to be made, the price per device becomes excessive. This thesis describes how a simple syringebased 3D-printer, in combination with an appropriate choice of materials, can reduce the delay between design and prototype and simplify fabrication of microsystems. This thesis suggest two types of materials that we propose be used in combination with 3D-printing to further develop microsystems for biology and biochemistry.Analytical applications in biology and biochemistry often contain electrodes, such as in gel electrophoresis. Faradaic (electrochemical) reactions have to occur at the metal electrodes to allow electron-to-ion transduction through an electrolyte-based system to drive a current when a potential is applied to the electrodes in an electrolyte-based system. These electrochemical reactions at the electrodes, such as water electrolysis, are usually problematic when miniaturizing devices and analytical systems. An alternative to metal electrodes can be electrochemicallyactive conducting polymers, e.g. poly(3,4-ethylenedioxythiophene) (PEDOT), which can be used to reduce electrolysis when driving a current through water-based systems. Paper 1 describes gel electrophoresis where the platinum electrodes were replaced with the conductive polymer PEDOT, without affecting the separation.Manufacturing and prototyping of microsystems can be simplified by using 3Dprinting in combination with a sacrificial material. A sacrificial template material can further simplify bottom-up manufacturing of more complicated forms such as protruding and overhanging structures. We showed in paper 2 that polyethylene glycol (PEG), in combination with a carbonate-based plasticizer, functions well as a 3D-printable sacrificial template material. PEG2000 with between 20 wt% and 30 wt% ethylene carbonate or propylene carbonate has properties advantageous for 3D-printing, such as shear-thinning rheology, mechanical and chemical stability, and easy dissolution in water.
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| 9. |
- Böhme, Solveig, 1987-
(författare)
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Fundamental Insights into the Electrochemistry of Tin Oxide in Lithium-Ion Batteries
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims to provide insight into the fundamental electrochemical processes taking place when cycling SnO2 in lithium-ion batteries (LIBs). Special attention was paid to the partial reversibility of the tin oxide conversion reaction and how to enhance its reversibility. Another main effort was to pinpoint which limitations play a role in tin based electrodes besides the well-known volume change effect in order to develop new strategies for their improvement. In this aspect, Li+ mass transport within the electrode particles and the large first cycle charge transfer resistance were studied. Li+ diffusion was proven to be an important issue regarding the electrochemical cycling of SnO2. It was also shown that it is the Li+ transport inside the SnO2 particles which represents the largest limitation. In addition, the overlap between the potential regions of the tin oxide conversion and the alloying reaction was investigated with photoelectron spectroscopy (PES) to better understand if and how the reactions influence each other`s reversibility.The fundamental insights described above were subsequently used to develop strategies for the improvement of the performance and the cycle life for SnO2 electrodes in LIBs. For instance, elevated temperature cycling at 60 oC was employed to alleviate the Li+ diffusion limitation effects and, thus, significantly improved capacities could be obtained. Furthermore, an ionic liquid electrolyte was tested as an alternative electrolyte to cycle at higher temperatures than 60 oC which is the thermal stability limit for the conventional LP40 electrolyte. In addition, cycled SnO2 nanoparticles were characterized with transmission electron microscopy (TEM) to determine the effects of long term high temperature cycling. Also, the effect of vinylene carbonate (VC) as an electrolyte additive on the cycling behavior of SnO2 nanoparticles was studied in an effort to improve the capacity retention. In this context, a recently introduced intermittent current interruption (ICI) technique was employed to measure and compare the development of internal cell resistances with and without VC additive.
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| 10. |
- Edberg, Jesper, 1988-
(författare)
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Flexible and Cellulose-based Organic Electronics
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic electronics is the study of organic materials with electronic functionality and the applications of such materials. In the 1970s, the discovery that polymers can be made electrically conductive led to an explosion within this field which has continued to grow year by year. One of the attractive features of organic electronic materials is their inherent mechanical flexibility, which has led to the development of numerous flexible electronics technologies such as organic light emitting diodes and solar cells on flexible substrates. The possibility to produce electronics on flexible substrates like plastic or paper has also had a large impact on the field of printed, electronics where inks with electronic functionality are used for large area fabrication of electronic devices using classical printing methods, such as screen printing, inkjet printing and flexography.Recently, there has been a growing interest in the use of cellulose in organic and printed electronics, not only as a paper substrate but also as a component in composite materials where the cellulose provides mechanical strength and favorable 3D-microstructures. Nanofibrillated cellulose is composed of cellulose fibers with high aspect-ratio and diameters in the nanometer range. Due to its remarkable mechanical strength, large area-to-volume ratio, optical transparency and solution processability it has been widely used as a scaffold or binder for electronically active materials in applications such as batteries, supercapacitors and optoelectronics.The focus of this thesis is on flexible devices based on conductive polymers and can be divided into two parts: (1) Composite materials of nanofibrillated cellulose and the conductive polymer PEDOT:PSS and (2) patterning of vapor phase polymerized conductive polymers. In the first part, it is demonstrated how the combination of cellulose and conductive polymers can be used to make electronic materials of various form factors and functionality. Thick, freestanding and flexible “papers” are used to realize electrochemical devices such as transistors and supercapacitors while lightweight, porous and elastic aerogels are used for sensor applications. The second focus of the thesis is on a novel method of patterning conductive polymers produced by vapor phase polymerization using UV-light. This method is used to realize flexible electrochromic smart windows with high-resolution images and tunable optical contrast.
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